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Merge pull request #7137 from MartinZikmund/dev/mazi/startstopevent-s…
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,90 @@ | ||
| #nullable enable | ||
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| using System; | ||
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| namespace Uno.Helpers; | ||
|
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| /// <summary> | ||
| /// Creates a wrapper around a generic event, which needs to be synchronized | ||
| /// and needs to run an action when first subscriber is added and when | ||
| /// last subscriber is removed. The operations executed when first subscriber | ||
| /// is added and last subscriber is removed will execute within | ||
| /// a synchronization lock, so please avoid blocking within the actions. | ||
| /// </summary> | ||
| internal class StartStopDelegateWrapper<TDelegate> | ||
| where TDelegate : Delegate | ||
| { | ||
| private readonly object _syncLock; | ||
| private readonly Action _onFirst; | ||
| private readonly Action _onLast; | ||
|
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| /// <summary> | ||
| /// Creates a new instance of start-stop delegate wrapper. | ||
| /// </summary> | ||
| /// <param name="onFirst">Action to run when first subscriber is added. | ||
| /// This will run within a synchronization lock so it should not involve blocking operations.</param> | ||
| /// <param name="onLast">Action to run when last subscriber is removed. | ||
| /// This will run within a synchronization lock so it should not involve blocking operations.</param> | ||
| /// <param name="sharedLock">Optional shared object to lock on (when multiple events | ||
| /// rely on the same native platform operation.</param> | ||
| public StartStopDelegateWrapper( | ||
| Action onFirst, | ||
| Action onLast, | ||
| object? sharedLock = null) | ||
| { | ||
| _onFirst = onFirst; | ||
| _onLast = onLast; | ||
| _syncLock = sharedLock ?? new object(); | ||
| } | ||
|
|
||
| /// <summary> | ||
| /// Backing delegate. | ||
| /// </summary> | ||
| public TDelegate? Event { get; private set; } | ||
|
|
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| /// <summary> | ||
| /// Indicates if there is at least one active subscription. | ||
| /// </summary> | ||
| public bool IsActive => Event != null; | ||
|
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| /// <summary> | ||
| /// Synchronization lock. | ||
| /// </summary> | ||
| public object SyncLock => _syncLock; | ||
|
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| /// <summary> | ||
| /// Adds a handler. | ||
| /// </summary> | ||
| /// <param name="handler">Handler.</param> | ||
| public void AddHandler(TDelegate handler) | ||
| { | ||
| lock (_syncLock) | ||
| { | ||
| var firstSubscriber = Event == null; | ||
| Event = (TDelegate)Delegate.Combine(Event, handler); | ||
| if (firstSubscriber) | ||
| { | ||
| _onFirst(); | ||
| } | ||
| } | ||
| } | ||
|
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| /// <summary> | ||
| /// Removes a handler. | ||
| /// </summary> | ||
| /// <param name="handler">Handler.</param> | ||
| public void RemoveHandler(TDelegate handler) | ||
| { | ||
| lock (_syncLock) | ||
| { | ||
| if (Event != null) | ||
| { | ||
| Event = (TDelegate?)Delegate.Remove(Event, handler); | ||
| if (Event == null) | ||
| { | ||
| _onLast(); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } |
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