58 lines
2.0 KiB
Plaintext
58 lines
2.0 KiB
Plaintext
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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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----
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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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----
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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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== See
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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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