如何檢測XAML Slider何時完成？

Question

在XAML中我有<Slider />。它有ValueChanged事件。每次更改Value都會觸發此事件。我需要檢測價值變化何時結束。 LostFocus，PointerReleased不是正確的事件。我如何檢測這個？

Answer 1

您可以創建一個新的類，並從滑塊繼承。從那裏開始，您可以查找Thumb控件&監聽您想要的事件。

像這樣的東西應該工作：

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 2

我在Windows8/WinRT上使用Slider也有類似的問題。

我的問題如下：我對ValueChanged事件做出了反應，並在每次觸發後執行持久操作（對文件異步寫入）。並因此陷入併發編輯異常。爲了避免這種情況，我使用了一個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(); 
    } 

不能直接檢測最終值是什麼，但你至少可以延遲操作，直到有兩次更新之間長時間的停頓（例如，在我的情況下，如果用戶拖動滑塊和停止，同時保持拖動2秒，無論如何都會觸發保存操作）。

Answer 3

您可以使用一對bool值isValueChanged和（如果可能，更改值，不用指針 ）isPressed;

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

初始化代碼：

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

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

Answer 4

XAML，的WinRT，Windows8.1和UWP：

PointerCaptureLost事件應適用於鼠標/觸摸
KEYUP事件鍵盤