advanced language concepts in c# david figge [email protected] extra session last update:...

Introduction When Windows Vista was introduced, it included a new graphical subsystem, code named Avalon Its purpose was to Provide a new state-of- the-art graphics API Supported through the DirectX module, which provides low-level graphics APIs for games, etc Designed to use hardware acceleration at a low level (when present) Windows 7 inherited this subsystem, too. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 3

What Is Windows Presentation Foundation? Windows Presentation Foundation (WPF) is the.Net component designed to leverage these new graphical capabilities. WPF is a graphical subsystem within.Net Introduced in.Net 3.0 WPF was designed to provide a single interface to support the flexibility and needs of todays modern applications. It works on Vista/Win7 and XP Vista/Win 7 has it automatically XP requires an update to have.Net 3.0 (minimum) Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 4

WPF Provides Unified Support for Standard Windows elements (dialog boxes, controls) Easy support for higher level graphics (gradient fills, etc) The ability to defining complex data representation at the presentation level The ability to easily combine graphics, animation, video, and audio Support for 2D and 3D graphics, including putting 2D graphics on a 3D surface This is a good example of an application that can be put together using the capabilities of WPF, including Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 5

Introduction So WPF takes several, disjointed APIs within the OS and put them under one presentation foundation Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 6 Windows Forms PDFWindows Forms/ GDI+ Windows Media Player Direct3D (DirectX) WPF Graphical interface (e.g. forms and controls) On-screen documents Fixed-format documents Images Video and audio Two-dimensional graphics Three-dimensional graphics Windows Forms (WinForms) is the.Net 1.x and 2.x solution to UI design. It basically provided layout capabilities for standard Windows controls and ActiveX controls. Fixed Format Documents were typically displayed using something like Adobes PDF File Format. This allows documents to display on screen as they will on a printer. Images and 2D graphics were displayed using WinForms, sometimes with assistance from COM object technology. To use Video and Audio, you were delving into the Media arena, which is supported by Windows Media Player And if you wanted to get fancy 3D graphics, you had to use the DirectX technology WPF combines all these technologies into one presentation layer and allowing improved development and integration between all these elements. Questions so far? So lets see how this is integrated into.Net

.Net Architecture.Net Applications.Net Dev Tools.Net WCF (Indigo) WPF (Avalon) CardSpace (InfoCard) WF (WorkFlow) Common Language Runtime.Net 2.0 Base Class Libraries, ASP.Net 2.0, ADO.Net 2.0, WinForms 2.0 Windows OS (Windows Vista/7, XP, Server) PC Hardware At the very base, of course, we have the PC Hardware. The significant factor here is that for the first time the Windows presentation layer will make use of hardware accelereration provided by graphics cards The OS provides the ultimate interface between the application programs and the hardware.Net sits on top of the OS, and consists of a series of run-time and compile-time elements. Well come back to this in a minute.Net applications run on top of.Net. For developers, the.Net Development Tools are a key element in this structure, providing support for creation and debugging of.Net applications in many languages. One of the key elements within the.Net structure is the Common Language Runtime (CLR) providing just- in-time compiling, security, memory management, and a host of other services..Net 3.0 introduced Windows Communi- cations Foundation, providing support for server level and peer-to- peer network communi- cations. CardSpace provides identity verification technologies to.Net, tying together everything from Web Logins to Active Directory. Windows WorkFlow Foundation supports taking information through a series of steps (the work flow) to its completion. WPF Sits beside these technologies providing the UI support for.Net applications and integrating these into.Net, the Operating System, and ultimately the hardware. Lets look more closely at the WPF components. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 7

.Net Applications.Net Dev Tools.Net OS PC Hardware WPF Components PresentationFramework PresentationCore Common Language Runtime Milcore Media Integration Layer DirectX User32/GDI Kernel WPF ComponentNon-WPF.Net OS Component Codecs From the beginning of Windows, the presentation of a window and its components resided in the OS, through functions in the User32 and GDI modules, working in conjunction with the core OS kernel. As the need for more direct graphic programming came about (mostly from game developers), DirectX was developed as a fast, direct link to core level graphics capabilities of the OS and the hardware. All WPF output to the system occurs through DirectX. The Media Integration Layer, Milcore, is the component that ties WPF into DirectX Milcore is the one major component of WPF that is written in unmanaged code. This was needed for performance reasons, especially around timing of animations audio, video, and production of 2D and 3D graphics. Video and audio Codecs are used by Milcore, and are also written in unmanaged code. The Presentation Core layer provides the managed code interface into milcore, and implements the core services for WPF. The Presentation Foundation module implements the end user presentation features, including layouts, storyboard animations, and data binding. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 8 Still doing okay?

Under the Covers Lets take a quick look under the covers at WPF This will help us understand coding aspects as well UI Elements are maintained as a group of Visual objects Visual objects are maintained in a Composition Tree, managed by the MIL Each element of WPF creates and adds one or more Composition Nodes to the tree These nodes contain rendering instructions So the entire applications visuals are represented as a collection of Composition Nodes. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 9

UI Rendering So the MIL maintains the visual tree for each application Remember these dont contain visuals, they contain instructions used to render the visuals This allows the MIL to retain the visual tree for each application, so it becomes responsible for updating the graphics rather than continually calling into the application via a Paint method This also allows the application to update the visuals incrementally, as individual pieces change, rather than all at once like traditional Windows apps Animations become simple incremental changes applied based on a timer interval. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 10

UI Rendering So the MIL maintains the visual tree for each application The MIL has a dedicated thread that periodically updates the visuals as changes occur The MIL uses a painters algorithm that renders elements from back to front, allowing you to skip areas that are covered and handle complex aspects like transparency easily. The rendering of the UI is also assisted via the Graphics Processing Unit on the video adapter (if present) Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 11

Managing the UI: Properties WPF employs a data-driven system for displaying user content After the initial rendering, visual objects are updated via Properties These properties may represent data changes (like a new record to display), or any other visual aspect (like IsVisible) These properties can be set manually via code, or bound to an element and updated automatically Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 12

Managing the UI: Properties So, the visuals are largely customized by a collection of Properties These properties, however, also support an inheritance element Base level properties (like FontSize) are inherited by child elements So, when base properties are changed, child elements are notified as well This is also good, because elements may have dozens (or hundreds) of properties managing visuals, and this avoids each element retaining copies Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 13

Managing the UI: Properties Finally, the Property system also supports Attached Properties An example: A Grid Panel allows elements to be laid out in a Grid format (columns and rows) Each element on the grid has an attached property of the grid row and column This is only because the grid is holding the element. This isnt inheritance, because on a different layout, the properties may change Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 14

Under the Covers So each application has two threads One for rendering and repainting This one generally runs by itself without developer help And one for managing the UI Input from the user, changes you cause programmatically This is important, because any processing you do in your program takes place in the UI thread, effectively freezing the UI So any type of lengthy operations (that might be felt by the UI) should be done in a background thread Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 15

But Wait, Theres More! Some additional aspects worth discussing (and we will over the next several slides): Graphical Services Interoperability Media Services Animations Data Binding Annotations Imaging Documents Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 16

Graphical Services All graphics (including windows) are through Direct3D, providing A unified way to displaying from simple (Win32 level) graphics to complex 3D graphics The ability to offload graphics tasks to the Graphics card GPU This can reduce the workload on the computer's CPU. Use of vector-based graphics, which allow lossless scaling. Supports 3D model rendering and interaction in 2D applications. Allows interactive 2D content to be overlaid on 3D surfaces natively (cool stuff!). Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 17

Interoperability WPF provides interoperability with the Windows API Via hosting, one can use Windows Presentation Foundation inside existing Win32 code Or one can use existing Win32 code inside Windows Presentation Foundation. Interoperability with Windows Forms is also possible through the use of the ElementHost and WindowsFormsHost classes. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 18

Media Services WPF provides shape primitives for 2D graphics Also provides a built-in set of brushes, pens, geometries, and transforms. It also supports 3D UI, 3D documents, and 3D media. Supports most common image formats. Supports video formats WMV, MPEG and some AVI files by default Because Windows Media Player is running underneath, WPF can use all the codecs installed for it. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 19

Animations Time-based animation. Scene redraws are time triggered. Isnt affected by CPU speed and load Presentation timers are initialized and managed by WPF. Scene changes coordinated via storyboards. This makes them easy to code Animations can be triggered by other external events, including user action. Ships with a set of predefined effects, such as fade out for all controls. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 20

Data binding WPF supports three types of data binding: One time: where the element ignores updates One way: where the element has read-only access to data. Two way: where the element can read from and write data LINQ queries can act as data sources for data binding. Binding of data has no bearing on its presentation. WPF provides data templates to control presentation of data. Base controls provided by WPF: buttons, menus, grids, list boxes, etc. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 21

Annotations Annotations can be applied on a per- object basis via WPFs Document or FlowDocument element. WPF only provides the capability for creating, storing and managing annotations Each application must expose the UI on their own. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 22

Imaging WPF uses the native Windows Imaging Component (WIC) code and APIs This means developers can write image codecs for their specific image file formats. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 23

Effects WPF provides for bitmap effects Although.Net 3.5+ and hardware support required Special effects such as drop shadows and blurring are built in. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 24

Documents WPF natively supports paginated documents. It provides the DocumentReader class, which is for reading fixed layout documents. The FlowDocumentReader class offers different view modes such as per-page or scrollable It also reflows text if the viewing area is re sized. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 25

UI Separation So, clearly, WPF is bringing a lot of power to the UI and code development table. Another direction that WPF used was to separate the design of the UI from the code to support that UI This is a method that was introduced with ASP UI Design elements are stored in one file Code to support the UI is stored in a Code Behind page with the same name Visual Studio handles all the naming and management details Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 26

In WPF, the design elements are defined in a file with a XAML extension Rhymes with Camel Stands for eXtended Application Markup Language This is an XML-based document that has definitions for all the UI elements of a window Each window has its own xaml page The Design Page

The Code Behind Page The Code Behind page contains code that supports the UI Its usually best to keep this to code just required to support the windows UI Avoid putting business logic in this file This decouples the business logic from the UI elements

Why This Separation? The purpose behind this separation is to allow the UI design and the support code to be done as separate processes UI design is a specific skill from programming And, typically, programmers are not good UI designers So this separation really allows UI designers and programmers to have the ability to work together, but not work in the same files Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 29

Lets Give it a Try! At its simplest level, WPF can be very easy to work with Visual Studio provides an easy form design mode that allows for simple drag-and-drop functionality You dont need to work with the Xaml code until you want something more advanced In this example, well have a label, a text box, a button, and a message box Well do this together as a class Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 30

Our First WPF App Create a new WPF Windows app called Birthday Drag the controls from the Toolbox and drop them onto the form as shown Note how the xaml code changes as you add the controls Use the Properties window to set The Content of the label to Your name: The Content of the button to Todays My Birthday! Double-click on the button to go to its handler in the code-behind page. Code: MessageBox.Show(Happy Birthday, + textBox1.Text + !); Give it a try! Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 31

Lets See What Weve Got Lets take a look at some of the elements that make up this program First, looking at the code page (Window1.xaml.cs) Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 32

Code Example Window1.xaml.cs using System;... namespace Birthday { ///... public partial class Window1 : Window { public Window1() { InitializeComponent(); } private void button1_Click(object sender, RoutedEventArgs e) { MessageBox.Show("Happy Birthday " + textBox1.Text + "!"); } Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 33 The first thing we see is the definition of the Window1 class. This is derived from the C# Window class, which encapsulates the functionality of a Window Note the keyword partial. This means that theres more class definition somewhere else in the project. In this case, the rest of the class is in a system generated at each build from the xaml code The primary element in that system generated file is the InitializeComponent function. The purpose of this function is to create the window based on the instructions in the xaml code. So, although we cant edit this function directly, we control whats in that function by modifying the xaml code. Lets take a look at the xaml code

.. Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 34 As we discussed, xaml is specific style of xml. Our root element is the Window tag, stating that this xaml code describes a window (there are other options, which well get to) This defines the class thats associated with the window (the Window1 class in the Birthday namespace) Still in the Window tag, were setting some properties of the Window its title and size. We can add more if we need to. And heres the closing tag of the root element Window. Inside the Window, we have a Grid element. A grid is one of several layout elements, which are responsible for positioning and supporting other elements (like controls). Inside the Grid tags we find">

Code Example Window1.xaml ... Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 34 As we discussed, xaml is specific style of xml. Our root element is the Window tag, stating that this xaml code describes a window (there are other options, which well get to) This defines the class thats associated with the window (the Window1 class in the Birthday namespace) Still in the Window tag, were setting some properties of the Window its title and size. We can add more if we need to. And heres the closing tag of the root element Window. Inside the Window, we have a Grid element. A grid is one of several layout elements, which are responsible for positioning and supporting other elements (like controls). Inside the Grid tags we find

Your Name: Today's My Birthday Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 35 the controls for our app. So the grid owns the label, textbox, and button. And the grid, in turn, is owned by the window itself.">

Code Example Window1.xaml Your Name: Today's My Birthday Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 35 the controls for our app. So the grid owns the label, textbox, and button. And the grid, in turn, is owned by the window itself.

This layered approach is important, and generally reflects the way that a Window is created A Window consists of a 4 buttons (System, Minimize, Maximize, and Close button) on top of a Title window, all on top of that base window. Windows are ultimately composites of many windows layered on top of one another. So the xml-based xaml layout actually represents this layered window approach well So, as you work your way through the xaml code, you create a visual tree representing the visual elements of the window. The Layered Approach Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 36

The Event Handler Before we leave our Birthday program, lets go take a look at our Click handler. The handler is tied to the button by associating it with the Click event of the button (in the xaml code). Double-clicking on the element creates a handler for the default event. In the case of the button, this is the Click event You can also add other handlers by specifying the association in the xaml code (well do that later). Note the Name element that gives a unique identifier to this button, and is used in the default handlers name Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 37...

The Event Handler Now lets look at the actual event handler code All UI event handlers in WPF have two parameters Sender, which refers to the triggering element In this case, it would be the button Note that its passed as an Object, which means anything can be passed in the first parameter If you need use sender to access the button, youll need to cast it to a Button object Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 38... private void button1_Click(object sender, RoutedEventArgs e) { MessageBox.Show("Happy Birthday " + textBox1.Text + "!"); }...

The Event Handler Now lets look at the actual event handler code The other parameter is a type of EventArgs Derived from the base class EventArgs Has information that might be of use to the handler For example, MouseEventArgs, passed to MouseMove events, has the current mouse coordinates In this case, theres little useful information to the button click in RoutedEventArgs Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 39... private void button1_Click(object sender, RoutedEventArgs e) { MessageBox.Show("Happy Birthday " + textBox1.Text + "!"); }...

More WPF Basics As you can see as we just scratch the surface, there are many aspects to WPF There are too many to jump into immediately, but lets hit some of the basics before we move on Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 40

WPF Panels In the Birthday program, we used the Grid panel WPF provides several different panels to suit various needs: PanelUse GridAllows absolute placement CanvasUser defined contents DockPanelAllows docking of panels (Left,Top,Right,Bottom) StackPanelStacks elements (vertical or horizontally) UniformGridPlaces elements into uniform sized columns, rows WrapPanelAutomatically wraps elements as space fills up Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 41

Primary Controls WPF provides standard controls, as well as some more complex controls Alright. Enough talk. Lets take a look at a Calculator program Ive got written in WPF CategoryElements Std Window Controls Label, Textbox, Listbox, Combobox, Button, Checkbox, GroupBox, RadioButton, Scrollbar Complex ControlsListView, Border, Canvas, Image, ProgressBar, Tab, TreeView, Slider, Rich Edit Box, Toolbar. Statusbar Basic shapesEllipse, Rectangle Sub-ContainersScrollView, DocumentViewer Last Update: 2/11Copyright (C) 2011 by David Figge. All Rights Reserved.Page 42

Calculator Program Lets talk about This basic calculator was made similar to how one would make it in WinForms Drag and drop controls, etc. Adding Styles A style allows you to control the way controls look and operate directly from the xaml Uncomment the style Keep storyboard and its reference commented out WPF also allows you to specify animations Either through code or from the xaml itself Uncomment the storyboard and its reference Last Update: 3/09Copyright (C) 2009 by David Figge. All Rights Reserved.Page 43

WPF Summary So what you saw just scratched the surface, but as you can see WPF gives Ability to customize control look and feel (much more than WinForms) Ability to add 3D graphics, multimedia,etc Ability to add animations easily Inclusion of images, manipulations Built-in support for documents (pdf) Questions on our brief introduction? Last Update: 3/09Copyright (C) 2009 by David Figge. All Rights Reserved.Page 44

Delegates Delegates are a software mechanism to allow function call choices to be made at runtime. A reasonable analogy can be drawn from politics... Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 46

Delegates The President is generally a pretty busy man. Often when something unexpected arises, such as the death of a head of state, the President is unable to attend, and must send his representative The Vice President, Secretary of State, 1st Lady... This person is a delegate, and represents our country for that event The President defines in advance what responsibility will be delegated (i.e. attend the funeral), and what parameters will be passed (i.e. condolences, kind words) He then assigns a specific person to act as that delegate at runtime, or as the situation occurs. In the same way that the President defines and assigns a delegate at runtime, C# delegates are used to make function call decisions at runtime. Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 47

Delegates So delegates are used in situations where you need to execute a particular action, but you dont know in advance what method (or maybe even which object) youll use to call upon to execute it. A delegate is a variable that points to a specific kind of function in your code. For example, int function(double, double) This is very similar to a function pointer in C/C++ Delegates have many uses, but could probably be generalized into a couple of categories Predefining a function to call Callback Functions Lets talk about both of these a bit... Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 48

Predefining a Function to Call Sometimes you need to selection what function to call before youre actually ready to call the function For example, perhaps a program has a customizable toolbar, allowing the user to choose what tool (function) to call when the button is pressed By storing the function to call in a delegate, you can call it on demand easily without a complex switch or if/then statements User wants button to be Print User presses button Delegate = PrintDocument( ) Delegate executes PrintDocument Lets diagram an example along a timeline... Sometime during the running of the program, the user selects a button and assigns it to the Print functionality. They arent printing, just defining the button to print when pushed. At that point, the button for the delegate is assigned to the PrintDocument function. Meanwhile, the user continues to work with the document. When the user finally presses the Print button, we simply execute the delegate and the PrintDocument function is called. Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 49 Does that make sense?

Callbacks Functions A Callback is a term for a parameter to a function that is the address of another function. For an example, lets consider a sort function Sort functions have a challenge You can make the function be very specific, and sort integers and floats (and such), but that limits its usefulness You can make the function be very general (like sorting user-defined arrays or arrays of objects), but you dont have enough information about the objects to compare them This is where the Callback function enters Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 50

Callback Functions By including, as a parameter to Sort, the function it should use to compare items (and therefore put them in order), you can support any type of data the user wants to sort So we use the term Callback because the generic sort code calls back into your custom code to perform its task. Lets diagram this one, too... User Code System Code So your program is humming along, and it decides to call the Systems Sort method. You provide a callback function (setting the delegate parameter) of a function that will do the comparison of two objects. So as the system function is sorting, it needs to know which of two objects is greater. So it calls into your code (using the function you provided via the delegate parameter), and your code compares the items, returning the result to the sort function. During its processing, the sort code may call into your compare routine many times. Of course, your main program execution is halted waiting for the sort to be finished. When the sort is done, your program continues on normally, probably unaware of the calls to the compare routine. Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 51 Have I lost anyone?

Callback Functions So Callback functions are used to add runtime-based flexibility to otherwise pretty limited functions In these cases, the delegate is a parameter in the function (e.g. sort) These types of callbacks may be used synchronously (like our sort example, simply waiting until its done before continuing the main thread... Or asynchronously. where the called function starts a separate thread at the start, then returning immediately. In these cases, there may also be a callback to signify that the thread has completed A good example of asynchronous processing is connecting to an Internet site you dont want to hold up the main program until this is complete. You can simply call a Callback function when youre done, which signals the main program of the status. So weve talked a lot about delegates, lets look at an example... Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 52

Code Example Delegate Example delegate void GradeDelegate(); class Student { public void A() { Console.WriteLine(name + " got an A"); } public void B() { Console.WriteLine(name + " got a B"); } public void C() { Console.WriteLine(name + " got a C"); } public GradeDelegate Grade; public string name; public Student(string n) { name = n; }; } class TestClass { static void Main() { Student[] stds = new Student[1]; stds[0] = new Student(Bob); stds[0].Grade = stds[0].B; foreach (Student s in stds) s.Grade(); } } This is how we define a delegate. It is of type delegate, and the delegate is a void function with no parameters. These are functions well use in the delegate. They have to match the delegate signature (void functions with no parameters, in this case). Here I declare an array of Students, and initialize the first one to Bob. This is the syntax for initializing a delegate. You simply assign it the name of the function you want to use (include the object if its an instance method) Now, I can print out whatever grade is associated with the student by the same function call for each Student object. How are we doing? The next step is to define a variable to hold the function, a variable of type GradeDelegate. Weve called this variable Grade, and In this case each student will have a GradeDelegate that well execute to find out what grade they got. Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 53

Delegate Exercise Im going to go back to that WPF Calculator program we used earlier. As you use the calculator, you will enter the first operand, an operator (+,-,*,/), and then the second operand (like 3 * 4). You then press the = key to get the total. As it is now, when you press the +, -, *, or / key, the program remembers the operation that you select. Were going to modify this to use a delegate to hold the desired operation (Add, Subtract, Multiply, or Divide) until the = key is pressed. When it is, well simply call the delegate, passing in the two operands. Ready? Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 54

Multiple Delegations One of the great features of delegates is that you can use += with them So multiple functions can be associated with the delegate When the delegate function is called, each function associated with it will be called in turn You can also remove an associated function with -= Delegates that use this feature are called Multicast delegates All delegates are capable of being multicast Lets see an example with our Student class we used a while ago Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 55

Code Example Multiple Delgations Example delegate void GradeDelegate(); class Student { public void A() { Console.WriteLine(name + " got an A"); } public void B() { Console.WriteLine(name + " got a B"); } public void C() { Console.WriteLine(name + " got a C"); } static public GradeDelegate Grade; public string name; public Student(string n) { name = n; } } class TestClass { static void Main() { Student[] stds = new Student[2]; stds[0] = new Student("Bob"); Student.Grade += new GradeDelegate(stds[0].B); stds[1] = new Student("Mary"); Student.Grade += new GradeDelegate(stds[1].A); Student.Grade(); } } Things have changed just a little. First, the Grade variable is now static (shared for all Student objects). This makes more sense with the += syntax. We now create 2 students. Note that I use += for adding the student to the Grade delegate. Now, I simply call Student.Grade() and it displays both students grade functions: Bob got a B Mary got an A Pretty slick, huh? Any questions? Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 56

Events So weve talked about delegates, now lets hit the closely-related subject of events. Events are an implementation of the Publisher/Subscriber design pattern (if that means anything to you). The concept behind events is that there are two pieces: a publisher (someone with information to share), and a subscriber (someone interested in that information). Lets take a look at an example to see if that clarifies things somewhat... Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 57

Publishers and Subscribers Lets consider the situation where we have a stock broker, Stock Broker Bill. Stock Broker Bill has information his clients want his buy/sell recommendations for stocks. Stock Broker Bill is the publisher of this information Some of Stock Broker Bills clients are interested in getting up-to-the-minute recommendations from him. The clients are the subscribers So Bill sets up an event: StockNotify. He uses this to send his buy/sell recommendations to his clients. Any client that is interested can register with the StockNotify event, and receive the buy/sell notifications. Lets see what this might look like... Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 58

Code Example Event Declaration Example public class StockBrokerBill { public delegate void dNotify(string ticker); public static event dNotify StockNotify; public static void Register(dNotify fcn) { StockNotify += fcn; } public static void Main(string[] args) {... // At the right time... StockNotify(MSFT); } } This class represents Stock Broker Bill. Events are based on delegates (which define the format of the function). Here we declare a delegate dNotify... And then the event itself(StockNotify) At some point, the event will be triggered like this (announcing that Microsoft stock is going up) Also in the class is a function that registers a client with the StockNotify event. Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 59

Code Example Event Subscription Example class Bob { public void Notify(string ticker) { MessageBox.Show(Bob: Buy +ticker); } public Bob() { StockBrokerBill.Register(Notify); } } So Bob is a client of Stock Broker Bill, and wants to be notified of stock risings. He has a method called Notify that displays a message to buy. In the Bob class constructor, we register the Notify function with StockBrokerBill.StockNotify (via Register). When the stock rises, Bobs Notify function will be called, saying Bob: Buy MSFT Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 60

Events vs. Delegates So, if the syntax looks very similar to delegates, theres a reason Events, being based on delegates, use the same registration and calling process So whats the difference between Events and Delegates? Can you just use the delegate instead of the event? Well, from a technical standpoint, theres not much difference Events can only be called from the class that defined them So theres a bit of a security benefit Delegates as data elements cant be part of an interface, but events can be Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 61

Events vs. Delegates So most of the difference between Events and Delegates is conceptual, and by convention rather than language-enforced rules Delegates are generally used for local (within the same application) storage of a function Like the calculator Events are typically for providing outside access to an internal resource Like registering a function on a remote computer to Stock Broker Bills StockNotify Or where you wish to have a level of separation between classes in the same program Event (and Delegate) Caveats: The calling order is not predictable, and exceptions could potentially disrupt subsequent calls Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 62

Windows Events C# Events is the mechanism used to support Windows Events Windows programming like other GUI environments is different from programming in a procedural environment (like the DOS command prompt) In Windows programming, the system stays in control of your program allowing windows to be selected and manipulated and swapped between and the system notifies your program when you need to get involved This removes significant burden of Window management from the application developers job, and gives a consistent look and feel to all of Windows Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 63

Windows Events A good example of this is our WinCheckbook program Windows handles the basic Windows mechanics moving a window, resizing, swapping between applications. Windows handles displaying of the pull-down menus, windows, buttons, etc., but when the user clicks on a button, only your program knows what to do So at that point, Windows contacts your program and tells it the user clicked on the Export button. You can then respond to the message and execute the export code In C#, the mechanism that Windows uses to support this messaging scheme is Events Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 64

Windows Events Windows defines hundreds of events that can occur during the running of a program You can be notified when the window is resized, moved, minimized, maximized, switched to, switched from, clicked on, etc. The trick to Windows programming is knowing what events occur and the order in which they happen So Windows makes all these events available to you by creating C# Events that you can register with If you want to know if a user clicks on a menu item, you register a function with the Click event of the menu item. That way, your code is called when the user clicks on the menu Lets take a look at our WinCheckgook program and see just where that code actually is for that Export button... Questions on Events? Last Update: 4/11Copyright (C) 2010 by David Figge. All Rights Reserved.Page 65

Design Patterns Design Patterns are a collection of real-world solutions that have been proven in the industry over time to solve common problems Recognize that were not talking about a class or object. Were talking about repeating patterns of how objects have been created, organized, and have interacted with each other to solve common, repeating problems. These patterns are in use all around us. No one person invented them. Theyre simply common solutions to common problems. As these patterns become recognizable to you, you will be better able to identify key components, and potential issues to consider when solving these common issues.

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 68 Design Patterns In the mid-90s Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides also known as the gang of four (or GoF) cataloged the basic patterns industry continued to use and reinvent. The result is their book Design Patterns (our text). The patterns they identified are generally considered the foundations for all other patterns. The GoF categorized the patterns in 3 groups Creational Having to do with creating objects Structural Having to do with program structure Behavioral Having to do with object interactions There are too many patterns to look at in depth, but lets take an overview look at these categories and look in detail at some of the more common patterns...

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 69 Creational Patterns Creational design patterns abstract the object instantiation process. Used correctly, they help make a system independent of how its objects are created, composed, and represented. Lets take a look at two common patterns: The Abstract Factory, and The Singleton

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 70 The Abstract Factory The Abstract Factory pattern is when a client rather than creating an object itself delegates that to an intermediary object. By doing this, the intermediary takes responsibility for determining what the best object is given the current state of the system. A computer example might be making a call to the OS to return a scrollbar object. If Im under Windows, that scrollbar will look different than if Im under Mac OS. By deferring the decision to the operating system, it was able to create the appropriate one given the current system The client then agrees to use the returned object according to the common public interface for both scrollbars.

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 71 The Abstract Factory A real life example (although the book focuses on object oriented software versions of these patterns, I just wanted to show that these patterns dont only apply to software, but to real life as well): When you call a travel agent, you are delegating the creation of your tickets, hotel, car, etc to them. The travel agent creates these items for you and returns them to you after they have been created. You then use the tickets with no further involvement from the travel agent. Get the idea?

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 72 Singleton A Singleton is a class where only one object of that type is allowed to exist in the system. A good example of this is a print queue. If multiple print queues were sending jobs to the same printer, jobs would get intermixed and it would be a mess Singletons are usually achieved by having a static creation function (not a constructor) that a) if no objects exist creates one, otherwise b) returns the existing one. At that point, all interaction with that object type takes place through that single global point of access.

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 73 Structural Patterns Structural Patterns deal with how classes and objects are combined to create larger solutions. Lets take a look at four common patterns: The Adapter The Bridge The Facade The Proxy

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 74 The Adapter Also known as a wrapper, the adapters job is to translate the interface of the target class into an interface that the client wants. It fits in between the client and the target, and simply translates method calls between the two. The queue template and the stack template are simply adapters on top of a vector that provide a queue and stack based interface to a client. Adapters are typically derivations of the target class, but doesnt have to be. Another example is the device that lets 3-prong plugs go into 2-prong electrical outlets (an adapter).

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 75 The Bridge Whereas the Abstract Factory isolated clients from the creation of objects, the Bridge is used to isolate a client completely from the details of an implementation...to separate what you would like from how it is done. So where the Abstract Factory simply created an object, the Bridge is used as an intermediary for an entire process How about an example: I have a car hands free phone system in my car, using Bluetooth wireless technology With this technology, the hands free unit can work with any bluetooth enabled cell phone that wants to use it The hands free knows how to ask a bluetooth phone to make a call, and The bluetooth phones lets the hands free interact with that phone call, but isolates it from how the phone makes the call. This decoupling of the request from the service provider allows me to use any bluetooth phone with my hands free. Lets try to diagram this just a little...

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 76 The Bridge Client InterfaceProvider So we start with a client, and a provider. We also have an interface object, which takes on the responsibility for the logical connection between the client and the provider. In the case of my hands-free, thats the bluetooth interface (half on the client, half on the provider were dealing with concepts, not detailed implementation). The client wants a service provided. In the case of my hands free, it wants to place a phone call. So the client makes the request to the interface object: place a call The interface calls to a provider object which creates the requested connection, perhaps passing back a connection object or identifier. This way the client can refer to the process it started for subsequent calls. The interface then returns this object or identifier to the client. The benefit comes when we swap out the provider object with another one. (e.g. we swap one phone for another) This can be done without shutting down the system. The same request is make, but this time a different provider serviced the request (a different phone) So the benefit of the Bridge is that we have the ability to separate the provider from the client. This allows us to create objects independent of the code platform on the client side, and allows the client to evolve separately from the objects it requests. Making sense?

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 77 The Facade Creating lots of powerful, focused objects is a good thing, but systems can get large enough where dealing many interfaces becomes difficult. The Facade inserts itself in between the client(s) and all the objects, and provides a unified interface into the subsystem. FacadeFacade Client Classes Subsystem Classes

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 78 The Proxy A Proxy is any object that represents itself to be another object. There are a variety of reasons to do this, including security, load management, and remote representation. A good example of a proxy is a firewall. To the Internet, the firewall is your system. But the firewall handles flow control and security issues so that your system doesnt have to and isnt exposed to the dangers of the Internet. System Security Proxy

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 79 Behavioral Patterns Behavioral Patterns deal with algorithms and the assignment of responsibilities between objects. So its not just the structure of the class and object hierarchies, but how they communicate and interact with one another. Lets take a look at three common behavioral patterns: The Command The Iterator, and The Observer

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 80 The Command The concept behind the Command pattern is to pass a function to another object and have it called from there. For example, when we created our Populate static method, we passed a pointer to a function that added the Appt to the Storage object. The command pattern is the object oriented version of that concept Where the function pointer is encapsulated into an object and passed around like other objects. By placing the command into an object, you can store the object, like putting it into a queue of commands that the system must address.

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 81 Undo Stack EMPTY The Command A good example of a Command pattern is and undo operation When the user changes an element on the display, you first save the state of the existing display perhaps a series of commands to reset the current change to the way it was into an object. This restore state command object is then placed into an Undo stack. You may push perhaps 5 of these items onto the stack. When the user decides to undo all five, each element is taken in turn and executed, putting back the state where the previous undo can restore from. Remove H _ H_HE_HEL_HELL_HELLO_ Display Controller Object Remove ERemove L Remove O Does it make sense how Command works?

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 82 The Iterator The iterators job is to sequentially navigate a container while hiding the underlying container implementation We used iterators when we used Linq No matter whether the data came from internal objects or a database, we accessed the data the same way Iterators are very common in database systems, and are also called cursors.

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 83 The Observer Also known as Publish-Subscribe, the Observer pattern has two parties One who is interested about some event that can or will occur (the subscriber), and One who notifies interested parties that the event has occurred (the publisher) A simple example is a calendars reminder option. You want to be reminded to leave in time for this class, so you subscribe to the Notify list when the appointments time comes up. When the time arrives, the system advises you with a reminder window. We also discussed it when we discussed eventsthe Broker Bill example Lets review that from an Observer pattern viewpoint...

Copyright (C) 2005 by David Figge. Unauthorized Use Prohibited. Page 84 The Observer A stock broker may (directly or indirectly) allow you to subscribe to a notification service. This service watches a particular stock, and when it rises beyond a certain level, the system publishes that information by notifying subscribers to pay attention to the stock This could be something as simple as triggering an email to a mailing list, or be a remote procedure executed over the Internet the implementation isnt essential to the pattern. Does Observer make sense to everyone? Questions on any of the patterns weve discussed?

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