c-jumpstart module 4

7/28/2019 C-Jumpstart Module 4

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04 | Features of C#, Part 3Jerry Nixon | Microsoft Developer EvangelistDaren May | President & Co-founder, Crank211


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Code Reflection and Information Working with Garbage Collection

Module Overview


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MVA

Code Reflection and Information


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Reflection inspects type metadata at runtime The type metadata contains information such as:

The type Name

The containing Assembly

Constructors

Properties

Methods Attributes

This data can be used to create instances, access valuexecute methods dynamically at runtime

What is Reflection?


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Two methods: Statically at compile time

Dynamically at runtime

How do I get Type data?


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There are two ways to dynamicallyinstantiate a type: Activator.CreateInstance

Calling Invoke on a ConstructorInfo object(advanced scenarios)

How can I create an instance of a Type?


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Accessing a Property


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Invoking a Method


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Reflection (004)


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MVA

Working with Garbage Collection


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Garbage collection is automatic memory manageme De-referenced objects (orphans) are not collected imbut periodically.

Many factors influence Garbage Collection frequency

Not all orphans are collected at the same time

Garbage Collection is computationally expensive

What is Garbage Collection?


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In most cases, let the Garbage Collectordo its thing. For a periodic activity it may makesense to force the collector to run:

Windows Service

Forcing Garbage Collection


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If an object consumes many resources when instantia If you want to proactively free expensive resources

You dont want to force a full collection cycle.

Force Garbage Collection? Implement IDisposable.

But I want to help!


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Some objects need explicit code torelease resources. The IDisposable interface marks thatthese types implement the Disposemethod. The simple dispose pattern works wellfor simple scenarios and sealed types

use the advanced pattern in most cases.

Disposable Objects


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Use for any non-trivial disposableobject.

Advanced Dispose Pattern


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The using keyword provides a usefulshortcut for invoking Dispose on typesthat implement IDisposable.

Using a shortcut

l


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Close May be functionally the same as Dispose

May be a subset of the Dispose functionality

A closed object may be reopened IDbConnection

Stop is similar to Close May be restarted.

Timer, etc.

Dispose versus Close versus Stop


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Streams and Dispose (005)

M L k


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Despite having automatic memory management, it ispossible to create managed memory leaks.

Objects that fall out of scope may be referenced by oscope, keeping them alive. Events can be a common source of memory leaks:

Events can hold references to objects Solution! Unsubscribe from events proactively

Weak references can be used to avoid some memoryscenarios.

Memory Leaks

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Weak references create a reference that the Garbageignores.

The Garbage Collector will assume an object is eligibcollection if it is only referred to by weak references. To hold an object with only weak references, create a

variable referring to the weak reference value. This prevents collection until the local variable is out of sco

Weak References


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Memory Leaks (036)

M d l R


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Code Reflection and Information Working with Garbage Collection

Module Recap


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2013 Microsoft Corporation. All rights reserved. Microsoft, Windows, Office, Azure, System Center, Dynamics and other product names are or may be registered trathe U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee tprovided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTA

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