问题

我正在尝试播放声音文件并等待其完成后再退出调用*AVAudioPlayer.Play()*的函数。

我理解有一个FinishedPlaying事件处理程序，可以初始化并相应地调用。

但该方法必须等待，而不会阻塞主线程...
这应该如何实现？

编辑 1：

我尝试使用ManualResetEvent，但 AVAudioPlayer 实例上的 FinishedPlaying 委托在播放结束时从未被调用...

NSError err;
ManualResetEvent playSoundFinished = new ManualResetEvent(false);    
var currentPlayer = new AVAudioPlayer(soundResource, "mp3", out err);
currentPlayer.FinishedPlaying += delegate { playSoundFinished.Set();};
currentPlayer.Play();
// 此调用应在事件被设置之前阻塞
DispatchQueue.DefaultGlobalQueue.DispatchSync(() => playSoundFinished.WaitOne(-1));

NSError err;
ManualResetEvent playSoundFinished = new ManualResetEvent(false);    
var currentPlayer = new AVAudioPlayer(soundResource, "mp3", out err);
currentPlayer.FinishedPlaying += delegate { playSoundFinished.Set();};
currentPlayer.Play();
// This call should block until the event is set
DispatchQueue.DefaultGlobalQueue.DispatchSync(() => playSoundFinished.WaitOne(-1));

答案1

得分: 1

以下是翻译好的部分：

"The delegate is never called because the call to DispatchQueue.DefaultGlobalQueue.DispatchSync blocks the main thread."

• 代理从未被调用，因为对 DispatchQueue.DefaultGlobalQueue.DispatchSync 的调用阻塞了主线程。

"The solution is to use a CancellationToken (or ManualResetEvent for that matter) that is canceled in the delegate and waited outside the method that plays the sound."

• 解决方案是使用 CancellationToken（或者也可以使用 ManualResetEvent），在代理中取消它，并在播放声音的方法之外等待它。

"Pseudo Code:"

• 伪代码：

"Playing the sound"

• 播放声音

"NSError err;"

• NSError err;

"this.currentPlayer = new AVAudioPlayer(soundResource, "mp3", out err);"

• this.currentPlayer = new AVAudioPlayer(soundResource, "mp3", out err);

"this.waitFinishedPlaying = new CancellationTokenSource();"

• this.waitFinishedPlaying = new CancellationTokenSource();

"this.currentPlayer.FinishedPlaying = delegate {waitFinishedPlaying.Cancel();};"

• this.currentPlayer.FinishedPlaying = delegate {waitFinishedPlaying.Cancel();};

"this.currentPlayer.NumberOfLoops = looping ? -1 : 0;"

• this.currentPlayer.NumberOfLoops = looping ? -1 : 0;

"this.currentPlayer.PrepareToPlay();"

• this.currentPlayer.PrepareToPlay();

"if (delay != 0)"

• if (delay != 0)

"this.currentPlayer.PlayAtTime(this.currentPlayer.DeviceCurrentTime + delay);"

• this.currentPlayer.PlayAtTime(this.currentPlayer.DeviceCurrentTime + delay);

"else"

• 否则

"this.currentPlayer.Play();"

• this.currentPlayer.Play();

"Outside the method that contains the code above:"

• 在包含上述代码的方法之外：

"try"

• 尝试

"The TimeSpan duration must be greater than the duration of the longest sound to be played."

• 时间跨度必须大于要播放的最长声音的持续时间。

"await Task.Delay(TimeSpan.FromSeconds(20), this.audioService.GetFinishedPlayingToken()).ConfigureAwait(true);"

• 等待 Task.Delay(TimeSpan.FromSeconds(20), this.audioService.GetFinishedPlayingToken()).ConfigureAwait(true);

"catch (OperationCanceledException)"

• 捕获 (catch) OperationCanceledException 异常

"GetFinishedToken() returns the waitFinishedPlaying instance initiated in the first block of code above."

• GetFinishedToken() 返回在上面的第一个代码块中初始化的 waitFinishedPlaying 实例。

"The only limitation to this solution is that the caller method must be async to await the Task."

• 此解决方案的唯一限制是调用方法必须是异步的，以等待任务。

NSError err;
this.currentPlayer = new AVAudioPlayer(soundResource, "mp3", out err);
this.waitFinishedPlaying = new CancellationTokenSource();
this.currentPlayer.FinishedPlaying = delegate {waitFinishedPlaying.Cancel();};
this.currentPlayer.NumberOfLoops = looping ? -1 : 0;
this.currentPlayer.PrepareToPlay();
if (delay != 0)
{
    this.currentPlayer.PlayAtTime(this.currentPlayer.DeviceCurrentTime + delay);
}
else
{
    this.currentPlayer.Play();
}

try
{
    // The TimeSpan duration must be greater than the duration of the longuest sound to be played.
    await Task.Delay(TimeSpan.FromSeconds(20), this.audioService.GetFinishedPlayingToken()).ConfigureAwait(true);
}
catch (OperationCanceledException)
{
}

答案2

得分: 0

ManualResetEvent 在内存中维护一个布尔变量。当布尔变量为 false 时，它会阻塞所有线程，当布尔变量为 true 时，它会解除阻塞所有线程。您可以通过将布尔值传递给构造函数来控制 ManualResetEvent 的初始状态：如果初始状态被标记为 true，则传递 true，否则传递 false。

您可以通过以下方式更改来解决这个问题：

ManualResetEvent playSoundFinished = new ManualResetEvent(true);