UIElement.IsMouseCaptured属性的应用

      一个只读属性，该值描述了此元素是否捕获到了鼠标，如果该值为true，则说明此元素捕获到了鼠标；否则，未捕获到（例如：当鼠标进入到一个Button的可视化范围之内，当Button按钮外观效果发生了变化时，则说明Button按钮捕获了鼠标，此时读取Button的IsMouseCaptured属性值，会得到true）。

例子1：如果鼠标捕获发生在别处，则鼠标捕获设置到该元素。 如果元素捕获了鼠标，则通过使用 null 输入调用 Mouse.Capture 来清除鼠标捕获

private void CaptureMouseCommandExecuted(object sender, ExecutedRoutedEventArgs e)
{
    MessageBox.Show("Mouse Command");
    IInputElement target = Mouse.DirectlyOver;

    target = target as Control;
    if (target != null)
    {
        if (!target.IsMouseCaptured)
        {
            Mouse.Capture(target);
        }
        else
        {
            Mouse.Capture(null);
        }
    }
}

例子二：当Button按钮捕获到鼠标时，我们设置Rectangle的填充效果为press效果。

<ControlTemplate TargetType="{x:Type Button}">
                            <Grid>
                                <Rectangle x:Name="recOk" StrokeThickness="0">
                                    <Rectangle.Fill>
                                        <ImageBrush ImageSource="../Images/MessageBoxImg/Ok.png"/>
                                    </Rectangle.Fill>
                                </Rectangle>
                            </Grid>
                            <ControlTemplate.Triggers>
                                <Trigger Property="IsMouseCaptured" Value="True"><!--当Button按钮捕获到了鼠标，则Button.IsMouseCaptured==true；--当Button.IsMouseCaptured==true，则Button按钮捕获到了鼠标-->
                                    <Setter TargetName="recOk" Property="Fill">
                                        <Setter.Value>
                                            <ImageBrush ImageSource="../Images/MessageBoxImg/Ok_press.png"/>
                                        </Setter.Value>
                                    </Setter>
                                </Trigger>
                            </ControlTemplate.Triggers>
                        </ControlTemplate>