sigcse intermediate topics in csharp 003

7/31/2019 SIGCSE Intermediate Topics in Csharp 003

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Intermediate topics in C#

Ivan Lumala

Academic Developer Evangelist

[email protected]


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Intermediate C#

1st class component support

Operator overloading

Versioning

Attributes


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Component Support

What defines a component? Properties, methods, events

Integrated help and documentation

Design-time and runtime information

C# has first class support

Not naming patterns, helper classes, etc.

Not external files

Easy to build and consume


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Properties

Access to private fields normally requiresaccessors and mutators

Properties allow access to private fields as ifthey were public

instead of:


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Indexers

Index an object as if it were an array

()

()

instead of:


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Delegates Object oriented function pointers

A reference type encapsulating a method signature andreturn value

Can point to multiple functions

Thread-safe + and - operations

Foundation for events

Delegate Multicast Delegate


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Events

Specialized multicast delegate

Represent a signal that somethinghas occurred in a program

Two main issues

Generating events

Consuming events


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EventsSourcing Define the event signature

Define the event and firing logic


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EventsHandling Define and register event handler


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Intermediate C#

Code example of Event Handling ina Windows Form

IsPrime app


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Intermediate C#

1st class component support

Operator overloading

Versioning

Attributes


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Rational Number, , 1

Rational r1 = new Rational(1,2);Rational r2 = new Rational(2,1);

Rational r3 = r1.AddRational(r2);

double d = Rational.ConvertToDouble(r3);

Rational r1 = new Rational(1,2);

Rational r2 = 2;

Rational r3 = r1 + r2;

double d = (double) r3;


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Rational Number Struct


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Implicit Conversions

No loss of data


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Explicit Conversions

Possible loss of precision and canthrow exceptions


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Operator Overloading

Static operators Must take its type as a parameter


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Equality Operators

.NET Framework equality support

.Equals() should use operator==()


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Intermediate C#

1st class component support Operator overloading

Versioning

Attributes


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Versioning

C# added some smarts to fix the versionproblem. Problem was that user could not express

versioning intent

C# can't guarantee versioning, but Can enable ( explicit override)

Can encourage ( smart defaults)

Impact on language is subtle but pervasive

Explicit interface implementation Overloading and overriding

readonly fields

Smart defaults for accessibility and virtuality

Event arguments packaged as objects


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Method Versioning in C#


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Intermediate C#

1st class component support Operator overloading

Versioning

Attributes


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Attributes

How do you associate information withtypes and members?

Documentation URL for a class

Transaction context for a method XML persistence mapping

Traditional solutions

Add keywords or pragmas to language Use external files, e.g., IDL, DEF

C# solution: Attributes


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Attributes

Appear in square brackets Attached to code elements


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Attribute Fundamentals Can be Intrinsic or Custom

Attributes are generic classes!

Easy to attach to types and members

Attributes can be queried at runtime

class HelpUrl : System.Attribute {public HelpUrl(string url) { }

}

[HelpUrl(http://SomeUrl/APIDocs/SomeClass)]class SomeClass { }

Type type = Type.GetType(SomeClass);

Attribute[] attributes =type.GetCustomAttributes();


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Creating Attributes

Attributes are simply classes Derived from System.Attribute

Class functionality = attribute

functionality

public class HelpURLAttribute: System.Attribute{

public HelpURLAttribute(string url) { }

public string URL { get { } }public string Tag { get { } set { } }

}


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Using Attributes

Just attach it to a class

Use named parameters

Use multiple attributes

[HelpURL(http://someurl/)]Class MyClass { }

[HelpURL(http://someurl/, Tag=ctor)]Class MyClass { }

[HelpURL(http://someurl/),HelpURL(http://someurl/, Tag=ctor)]

Class MyClass { }
http://someurl/http://someurl/http://someurl/http://someurl/http://someurl/http://someurl/


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Querying Attributes

Use reflection to query attributes

Type type = typeof(MyClass);

foreach(object attr in type.GetCustomAttributes())

{if(attr is HelpURLAttribute){

HelpURLAttribute ha = (HelpURLAttribute) attr;myBrowser.Navigate(ha.URL);

}}


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Resources

Newsgroup:microsoft.public.dotnet.languages.CSharp onmsnews.microsoft.com

Web sites:

http://msdn.microsoft.com/

Books

Inside C# MS Press

C# Language Specification MS Press C# How to Program Prentice Hall

Training developmentor, Wintellect

http://www.microsoft.com/net/training.asp
http://msdn.microsoft.com/http://msdn.microsoft.com/


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The .NET Framework in Curriculum

Multi-language runtime environmentUse the language you like

Access the same class libraries to do similartasks

Use a powerful IDE to access easy-to-uselearning tools

Visual Studio .NET Academic

Experience programming with .NET bybuilding your own Terrarium creature


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Microsoft Resources for Faculty

MSDN Academic Alliance

Check out MSDN AANew program from Microsoft

Software for computer science courses

Annual membership fee of $799 perdepartmentMembership runs from July-June

Web site that supports program:

(www.msdnaa.net)Visual Studio .NET AcademicAll the features of Visual Studio .NET

Professional plus Course Management

Tools


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Questions?


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