c# - 当鼠标指针不在窗口中时，如何接收 MouseWheel 事件？

Question

我注意到我的 MouseWheel 事件处理程序仅在鼠标指针位于窗口中时执行。即使指针在窗口外，我也希望它运行处理程序。

我的程序中只有一个窗口，它的 XAML 结构如下:

<Window ...
 MouseWheel = "Window_MouseWheel">
....
</Window>

Answer 1

为了在光标离开窗口时接收到鼠标事件，窗口需要“捕获”鼠标。它通过将自身传递给 Mouse.Capture() 来做到这一点方法。

请注意，如果您的程序窗口失去激活(即用户任务切换到其他程序)，它将失去鼠标捕获。如果您想在用户稍后重新激活窗口时再次自动跟踪鼠标滚轮，则需要专门处理它(即处理 Activated 事件)。

最后请注意，启用鼠标捕获后，通过鼠标与窗口的正常交互将不起作用，Alt-F4 也不起作用。您需要为用户提供一些额外的与程序交互的机制(例如处理按键事件)。

下面是一个简单的示例程序，展示了基本思想:

XAML:

<Window x:Class="TestSO30866523CaptureMouseWheel.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:l="clr-namespace:TestSO30866523CaptureMouseWheel"
        DataContext="{Binding RelativeSource={RelativeSource Self}}"
        Activated="Window_Activated"
        KeyDown="Window_KeyDown"
        MouseWheel="Window_MouseWheel"
        Title="MainWindow" Height="350" Width="525">
  <StackPanel x:Name="stackPanel1">
    <TextBlock Text="The window cannot be closed while mouse is captured."/>
    <TextBlock Text="Press Escape to stop capture. Press Return to resume capture."/>
    <TextBlock Text="{Binding Value, StringFormat=Value: {0}}"/>
    <TextBlock Text="{Binding MouseCaptured, StringFormat=Mouse is captured: {0}}"/>
  </StackPanel>
</Window>

C#:

public partial class MainWindow : Window
{
    public static readonly DependencyProperty ValueProperty = DependencyProperty.Register(
        "Value", typeof(int), typeof(MainWindow), new PropertyMetadata(0));
    public static readonly DependencyProperty MouseCapturedProperty = DependencyProperty.Register(
        "MouseCaptured", typeof(bool), typeof(MainWindow));

    public int Value
    {
        get { return (int)GetValue(ValueProperty); }
        set { SetValue(ValueProperty, value); }
    }

    public bool MouseCaptured
    {
        get { return (bool)GetValue(MouseCapturedProperty); }
        set { SetValue(MouseCapturedProperty, value); }
    }

    private readonly IInputElement _captureElement;

    public MainWindow()
    {
        InitializeComponent();

        _captureElement = this;

        Mouse.AddGotMouseCaptureHandler((DependencyObject)_captureElement, stackPanel1_GotLostMouseCapture);
        Mouse.AddLostMouseCaptureHandler((DependencyObject)_captureElement, stackPanel1_GotLostMouseCapture);
        Mouse.Capture(_captureElement);
        MouseCaptured = Mouse.Captured != null;
    }

    private void stackPanel1_GotLostMouseCapture(object sender, MouseEventArgs e)
    {
        MouseCaptured = Mouse.Captured != null;
    }

    private void Window_MouseWheel(object sender, MouseWheelEventArgs e)
    {
        Value += e.Delta;
    }

    private void Window_Activated(object sender, EventArgs e)
    {
        Mouse.Capture(_captureElement);
    }

    private void Window_KeyDown(object sender, KeyEventArgs e)
    {
        switch (e.Key)
        {
        case Key.Escape:
            Mouse.Capture(null);
            break;
        case Key.Return:
            Mouse.Capture(_captureElement);
            break;
        }
    }
}

当鼠标被捕获时，无论光标放在哪里，窗口都会响应鼠标滚轮事件。当鼠标未被捕获时，只有当光标在窗口上时才响应鼠标滚轮事件。