Waiting for UI re-rendering to complete

问题

I've actually got 2 similar problems here with no luck finding anything on the web.

Problem 1: Using a BackgroundWorker, I am updating the UI with the % done, but I am using the UserState because I want to report fraction of a percent. The problem is, depending on the inputs, sometimes updates happen rarely (a percent every couple seconds) and other times very fast (triggering fractional % updates many times a second). In the latter case, I'm getting a stack overflow (no pun intended) issue. I'm guessing the ProgressChanged event is just getting called too much. This is for now prototype code and I'm updating a TextBlock directly in the progressChanged event and not using ViewModels, but I will later. Not sure if this might be the problem. Is there a way to allow this progress changed event to get called how often it needs to, but say something like: if (!mytextblock.IsRendering()) mytextblock.text = newPercent;

That way it updates just when it's done drawing the last number. If percents get skipped, that's ok.

Problem 2: This is a personal project where I'm taking a screen capture, changing it in some way, then showing the changed image within the wpf program, and repeat continuously. Is there a way to say: GrabScreen EditImage UpdateUI WaitForUIToRender // <------- how do I do this? Repeat

thank you

回答1:

 public class TimedAction 
{
    public static void ExecuteWithDelay(Action action, TimeSpan delay)
    {
        var timer = new DispatcherTimer();
        timer.Interval = delay;
        timer.Tag = action;
        timer.Tick += timer_Tick;
        timer.Start();
    }

    static void timer_Tick(object sender, EventArgs e)
    {
        var timer = (DispatcherTimer)sender;
        var action = (Action)timer.Tag;

        action.Invoke();
        timer.Stop();
    }

    public static void ExecuteAfterRendering(Action action)
    {
        ExecuteAfterFrames(action, 3);
    }

    public static void ExecuteAfterFrames(Action action, int frames)
    {
        var timedAction = new TimedAction();
        timedAction._currentAction = action;
        timedAction._framesToWait = frames;
    }

    private Action _currentAction;
    private int _framesToWait;
    private int _currentFrame = 0;
    private TimedAction()
    {
        CompositionTarget.Rendering += CompositionTarget_Rendering;
    }

    private void Dispose()
    {
        CompositionTarget.Rendering -= CompositionTarget_Rendering;
    }

    void CompositionTarget_Rendering(object sender, EventArgs e)
    {
        _currentFrame++;
        if (_currentFrame == _framesToWait)
        {
            _currentAction.Invoke();
            Dispose();
        }
    }

}

来源：https://stackoverflow.com/questions/22386325/waiting-for-ui-re-rendering-to-complete