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MVVM Light EventToCommand不使用CaptureMouse

mvvm-light wpf

Nicholas Pappas · 技术社区 · 15 年前

我在EventToCommand上遇到了一些问题,它的行为不像我在CaptureMouse上期望的那样。

我有一个ResizeGrip,我在上面定义了几个EventToCommand:

<ResizeGrip Name="ResizeGrip" HorizontalAlignment="Right" VerticalAlignment="Bottom" Cursor="SizeNWSE">
<i:Interaction.Triggers>
  <i:EventTrigger EventName="MouseLeftButtonDown">
   <cmd:EventToCommand Command="{Binding ResizeStartCommand}" PassEventArgsToCommand="True" />
  </i:EventTrigger>
  <i:EventTrigger EventName="MouseLeftButtonUp">
   <cmd:EventToCommand Command="{Binding ResizeStopCommand}" PassEventArgsToCommand="True" />
  </i:EventTrigger>
  <i:EventTrigger EventName="MouseMove">
   <cmd:EventToCommand Command="{Binding ResizeCommand}" PassEventArgsToCommand="True" />
  </i:EventTrigger>
 </i:Interaction.Triggers>
 </ResizeGrip>

ResizeStartCommand = new RelayCommand<MouseButtonEventArgs>(
    (e) => OnRequestResizeStart(e));
ResizeStopCommand = new RelayCommand<MouseButtonEventArgs>(
    (e) => OnRequestResizeStop(e));
ResizeCommand = new RelayCommand<MouseEventArgs>(
    (e) => OnRequestResize(e),
    param => CanResize);

最后,我用我所有的逻辑来调整大小:

void OnRequestResizeStart(MouseButtonEventArgs e)
{
    bool r = Mouse.Capture((UIElement)e.Source);
    Console.WriteLine("mouse down: " + r.ToString());
}
void OnRequestResizeStop(MouseButtonEventArgs e)
{
    ((UIElement)e.Source).ReleaseMouseCapture();
    _canResize = false;
}
void OnRequestResize(MouseEventArgs e)
{
    Console.WriteLine("mouse move");
}
bool CanResize
{ get { return _canResize; } }

OnRequestResizeStart&OnRequestResizeStop命令工作正常,OnRequestResize工作正常。。。但只有当我真的在调整尺寸的时候。CaptureMouse似乎并没有实际将所有鼠标事件发送到ResizeGrip。

这是EventToCommand的限制,还是需要发生一些特殊的事情?

1 回复 | 直到 15 年前

John Bowen 15 年前

为什么要为此使用命令而不是标准的事件处理程序?这显然是属于代码隐藏的UI逻辑,而不是ViewModel。

****更新**

// this doesn't enforce the name but suggests it
[TemplatePart(Name = "PART_Resizer", Type = typeof(ResizeGrip))]
public class MyContainer : ContentControl
{
    private ResizeGrip _grip;

    public static readonly DependencyProperty ContainerDimensionsProperty = DependencyProperty.Register(
        "ContainerDimensions",
        typeof(Size),
        typeof(MyContainer),
        new UIPropertyMetadata(Size.Empty, OnContainerDimensionsChanged));

    private static void OnContainerDimensionsChanged(DependencyObject dObj, DependencyPropertyChangedEventArgs e)
    {
        MyContainer myContainer = dObj as MyContainer;
        if (myContainer != null)
        {
            Size newValue = (Size)e.NewValue;
            if (newValue != Size.Empty)
            {
                myContainer.Width = newValue.Width;
                myContainer.Height = newValue.Height;
            }
        }
    }

    public Size ContainerDimensions
    {
        get { return (Size)GetValue(ContainerDimensionsProperty); }
        set { SetValue(ContainerDimensionsProperty, value); }
    }

    static MyContainer()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(MyContainer), new FrameworkPropertyMetadata(typeof(MyContainer)));
    }

    public override void OnApplyTemplate()
    {
        _grip = Template.FindName("PART_Resizer", this) as ResizeGrip;
        if (_grip != null)
        {
            _grip.MouseLeftButtonDown += Grip_MouseLeftButtonDown;
            // other handlers
        }

        SizeChanged += MyContainer_SizeChanged;
        base.OnApplyTemplate();
    }

    void MyContainer_SizeChanged(object sender, SizeChangedEventArgs e)
    {
        // update your DP
    }
    ...
}

要使用它,您需要确保模板中有一个类型和名称与属性匹配的元素。

<local:MyContainer ContainerDimensions="{Binding Path=SavedSize}">
    <local:MyContainer.Template>
        <ControlTemplate TargetType="{x:Type local:MyContainer}">
            <Grid>
                <Border Background="{TemplateBinding Background}">
                    <ContentPresenter/>
                </Border>
                <ResizeGrip x:Name="PART_Resizer" HorizontalAlignment="Right" VerticalAlignment="Bottom"
                            Width="20" Height="20"/>
            </Grid>
        </ControlTemplate>
    </local:MyContainer.Template>
</local:MyContainer>

现在可以将此模板放在任何位置,因为它没有声明任何事件处理程序,因此独立于代码隐藏文件。现在,您的所有UI逻辑都封装在一个UI特定的类中,但仍然可以通过绑定来访问VM中所需的数据。

仔细想想,这就是你通常与内置控件交互的方式。如果您使用扩展器,您不希望将ToggleButton的单击传递到您的VM并尝试使控件从此处展开,但是您可能希望知道扩展器是打开的还是关闭的,因此有一个IsExpanded属性,您可以将其绑定并保存并作为数据加载。