Question

在XAML中，我有<Slider />。它有ValueChanged事件。每次更改Value时都会触发此事件。我需要检测值变化何时结束。 LostFocus，PointerReleased不是正确的事件。我怎么能发现这个？

Answer 1

XAML， WinRT ，Windows8.1和UWP：

PointerCaptureLost 事件应该适用于鼠标/触控
键盘 KeyUp 事件

Answer 2

您可以创建一个新类并从Slider继承。从那以后，你可以寻找拇指控制＆amp;听你想要的事件。

这样的事情应该有效：

public class SliderValueChangeCompletedEventArgs : RoutedEventArgs
{
    private readonly double _value;

    public double Value { get { return _value; } }

    public SliderValueChangeCompletedEventArgs(double value)
    {
        _value = value;
    }
}
public delegate void SlideValueChangeCompletedEventHandler(object sender, SliderValueChangeCompletedEventArgs args);

public class ExtendedSlider : Slider
{
    public event SlideValueChangeCompletedEventHandler ValueChangeCompleted;
    private bool _dragging = false;

    protected void OnValueChangeCompleted(double value)
    {
        if (ValueChangeCompleted != null)
        {
            ValueChangeCompleted(this, new SliderValueChangeCompletedEventArgs(value) );
        }
    }

    protected override void OnApplyTemplate()
    {
        base.OnApplyTemplate();
        var thumb = base.GetTemplateChild("HorizontalThumb") as Thumb;
        if (thumb != null)
        {
            thumb.DragStarted += ThumbOnDragStarted;
            thumb.DragCompleted += ThumbOnDragCompleted;
        }
        thumb = base.GetTemplateChild("VerticalThumb") as Thumb;
        if (thumb != null)
        {
            thumb.DragStarted += ThumbOnDragStarted;
            thumb.DragCompleted += ThumbOnDragCompleted;
        }
    }

    private void ThumbOnDragCompleted(object sender, DragCompletedEventArgs e)
    {
        _dragging = false;
        OnValueChangeCompleted(this.Value);
    }

    private void ThumbOnDragStarted(object sender, DragStartedEventArgs e)
    {
        _dragging = true;
    }

    protected override void OnValueChanged(double oldValue, double newValue)
    {
        base.OnValueChanged(oldValue, newValue);
        if (!_dragging)
        {
            OnValueChangeCompleted(newValue);
        }
    }
}

Answer 3

我在Windows8 / WinRT上使用Slider时出现了类似的问题。

我的问题如下：我对ValueChanged事件作出反应并在每次触发后执行持久操作（异步写入文件）。因此遇到并发编辑异常。为了避免这种情况，我使用了DispatcherTimer。

    //Class member
    private DispatcherTimer myDispatcherTimer = null;

    private void OnSliderValueChanged(object sender, RangeBaseValueChangedEventArgs e)
    {
        //I update my UI right away
        ...

        //If the dispatcher is already created, stop it
        if (myDispatcherTimer!= null)
            myDispatcherTimer.Stop();

        //Overwrite the DispatcherTimer and thus reset the countdown
        myDispatcherTimer= new DispatcherTimer();
        myDispatcherTimer.Tick += (sender, o) => DoSomethingAsync();
        myDispatcherTimer.Interval = new TimeSpan(0,0,2);
        myDispatcherTimer.Start();
    }

    private async void DoSomethingAsync()
    {
        await DoThatLongSaveOperation();
    }

你不能直接检测到最终值是什么，但你至少可以延迟操作，直到两次更新之间有一个长时间停顿（例如，在我的情况下，如果用户拖动滑块并在保持拖动2时停止）秒，保存操作无论如何都会被激活。）

Answer 4

你可以使用一对bool值isValueChanged和（如果可能的话，在不操纵指针的情况下改变值））isPressed;

private void Slider_ValueChanged(object s, RangeBaseValueChangedEventArgs e) {
    if (!isPressed) {
        AcceptChanges();
    } else {
        isValueChanged = true;
    }
}

初始化代码：

Window.Current.CoreWindow.PointerPressed += (e, a) => { isPressed = true; };

Window.Current.CoreWindow.PointerReleased += (e, a) => {
    isPressed = false;
    if (isValueChanged) AcceptChanges();
};

如何检测XAML滑块何时完成？

4 个答案: