ViewModel中的Task导致的内存泄漏

Question

我有以下代码，它会导致内存泄漏。

问题是任务，当我删除它时，一切都很好，并且 View 以及 ViewModel 都被 GCed。似乎任务保留了对 UpdateTimeDate 的引用，因此也保留了 ViewModel。我尝试了各种方法，但都没有奏效，希望有人知道或解释为什么会这样。

public class HeaderViewModel : Observable, IDisposableAsync
{
    public HeaderViewModel (IDateTimeProvider dateTimeProvider)
    {
        TokenSource = new CancellationTokenSource();

        ATask = Task.Run(
            async () =>
            {
                while(!TokenSource.Token.IsCancellationRequested)
                {
                    UpdateTimeData();
                    await Task.Delay(800);
                }

                IsDisposed = true;
            },
            TokenSource.Token);

        UpdateTimeData();

        void UpdateTimeData()
        {
            TimeText = dateTimeProvider.Now.ToString("HH:mm:ss");
            DateText = dateTimeProvider.Now.ToString("dd.MM.yyyy");
        }
    }

    public CancellationTokenSource TokenSource { get; set; }

    public bool IsDisposed { get; set; }

    public string TimeText
    {
        get => Get<string>();
        set => Set(value);
    }

    public string DateText
    {
        get => Get<string>();
        set => Set(value);
    }

    private Task ATask { get; set; }

    public async Task Dispose()
    {
        TokenSource.Cancel();

        while(!IsDisposed)
        {
            await Task.Delay(50);
        }

        TokenSource.Dispose();
        ATask.Dispose();
        ATask = null;
        TokenSource = null;
    }
}

这是基于 Timer 的解决方案，它也会导致内存泄漏：

public class HeaderViewModel : Observable, IDisposableAsync
{
    public HeaderViewModel(IDateTimeProvider dateTimeProvider)
    {
        DateTimeProvider = dateTimeProvider;

        ATimer = new Timer(800)
        {
            Enabled = true
        };

        UpdateTimeData(this, null);

        ATimer.Elapsed += UpdateTimeData;
    }

    public string TimeText
    {
        get => Get<string>();
        set => Set(value);
    }

    public string DateText
    {
        get => Get<string>();
        set => Set(value);
    }

    public bool IsDisposed { get; set; }

    private IDateTimeProvider DateTimeProvider { get; }

    private Timer ATimer { get; }

    public async Task Dispose()
    {
        ATimer.Stop();

        await Task.Delay(1000);

        ATimer.Elapsed -= UpdateTimeData;
        ATimer.Dispose();
        IsDisposed = true;
    }

    private void UpdateTimeData(object sender, ElapsedEventArgs elapsedEventArgs)
    {
        TimeText = DateTimeProvider.Now.ToString("HH:mm:ss");
        DateText = DateTimeProvider.Now.ToString("dd.MM.yyyy");
    }
}

Answer 1

我找到了解决方案。感谢 keuleJ，他发布了引导我的评论。因此，当您创建其中任何一个时，Task 或 Timer 正在捕获 ViewModel 的实例。防止它的方法是创建一个 WeakReference 并使用它：

public class HeaderViewModel : Observable, IDisposableAsync
{
    public HeaderViewModel(IDateTimeProvider dateTimeProvider)
    {
        DateTimeProvider = dateTimeProvider;

        UpdateTimeData();

        var weakReference = new WeakReference(this);

        Task.Run(
            async () =>
            {
                while(!((HeaderViewModel)weakReference.Target).IsDisposing)
                {
                    ((HeaderViewModel)weakReference.Target).UpdateTimeData();
                    await Task.Delay(800);
                }

                ((HeaderViewModel)weakReference.Target).IsDisposed = true;
            });
    }

    public bool IsDisposed { get; set; }

    public string TimeText
    {
        get => Get<string>();
        set => Set(value);
    }

    public string DateText
    {
        get => Get<string>();
        set => Set(value);
    }

    private IDateTimeProvider DateTimeProvider { get; }

    private bool IsDisposing { get; set; }

    public async Task Dispose()
    {
        IsDisposing = true;

        while(!IsDisposed)
        {
            await Task.Delay(50);
        }
    }

    private void UpdateTimeData()
    {
        TimeText = DateTimeProvider.Now.ToString("HH:mm:ss");
        DateText = DateTimeProvider.Now.ToString("dd.MM.yyyy");
    }
}

请注意，我也无法制作局部变量

(HeaderViewModel)weakReference.Target

当我这样做时，似乎发生了一些魔法，并且实例将再次被捕获。

Answer 2

您的 Dispose 任务似乎永远不会返回，这就是您的对象保留在内存中的原因。我将问题追踪到了

await Task.Delay(1000)

如果您根据这篇帖子 https://stackoverflow.com/a/24539937/3084003 更改它，它将起作用

await Task.Delay(1000).ConfigureAwait(false);