16f6c0aecf
Inline adoc files when they are included exactly once. Also fix language tags because this inlining gives us better information on what language the code is written in.
82 lines
2.4 KiB
Plaintext
82 lines
2.4 KiB
Plaintext
== Why is this an issue?
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Subscribing to events without unsubscribing later on can lead to memory leaks or even duplicate subscriptions, i.e. code which is executed multiple times by mistake.
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Even if there is no problem right now, the code is more difficult to review and a simple refactoring can create a bug. For example the lifetime of the event publisher could change and prevent subscribers from being garbage collected.
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There are patterns to automatically unsubscribe, but the simplest and most readable solution remains to unsubscribe from events explicitly using ``++RemoveHandler++``.
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This rule raises an issue when a class subscribes to an even using ``++AddHandler++`` without explicitly unsubscribing with ``++RemoveHandler++``.
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=== Noncompliant code example
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[source,vbnet]
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----
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Class MyEventProcucer
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Public Shared Event EventFired As EventHandler
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End Class
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Public Class MyEventSubscriber
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Implements IDisposable
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Public Sub New()
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AddHandler MyEventProcucer.EventFired, AddressOf c_EventFired 'Noncompliant
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End Sub
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Private Sub c_EventFired(sender As Object, e As EventArgs)
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End Sub
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Public Sub Dispose() Implements IDisposable.Dispose
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End Sub
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End Class
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----
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=== Compliant solution
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[source,vbnet]
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----
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Class MyEventProcucer
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Public Shared Event EventFired As EventHandler
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End Class
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Public Class MyEventSubscriber
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Implements IDisposable
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Public Sub New()
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AddHandler MyEventProcucer.EventFired, AddressOf c_EventFired
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End Sub
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Private Sub c_EventFired(ByVal sender As Object, ByVal e As EventArgs)
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End Sub
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Public Sub Dispose() Implements IDisposable.Dispose
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RemoveHandler MyEventProcucer.EventFired, AddressOf c_EventFired
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End Sub
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End Class
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----
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== Resources
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* https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/events/how-to-subscribe-to-and-unsubscribe-from-events#unsubscribing[How to subscribe to and unsubscribe from events (C# Programming Guide)]
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* https://michaelscodingspot.com/5-techniques-to-avoid-memory-leaks-by-events-in-c-net-you-should-know/[5 Techniques to avoid Memory Leaks by Events in C# .NET you should know]
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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Unsubscribe from this event explicitly with "RemoveHandler".
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=== Highlighting
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The ``++AddHandler++`` call.
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endif::env-github,rspecator-view[]
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