wpf 使用 ScrollViewer 单击并拖动滚动

Click and drag scrolling using ScrollViewer

提问by David

I would like to allow click and drag scrolling using a ScrollViewer(i.e. click anywhere in the ScrollViewerand drag up or down, and it will scroll accordingly)

我想允许使用 a 进行单击和拖动滚动ScrollViewer（即单击中的任意位置ScrollViewer并向上或向下拖动，它会相应地滚动）

I have a StackPanelnested inside a ScrollViewerand I already have the scrolling working. I believe I saw that answer somewhere, but I can't seem to find it anymore.

我有一个StackPanel嵌套在 a 中，ScrollViewer并且已经可以进行滚动。我相信我在某处看到过那个答案，但我似乎再也找不到了。

This has to be done using code only.

这必须仅使用代码来完成。

回答by Jens

Look at this code from Matt Hamilton:

看看Matt Hamilton 的这段代码：

public class TouchScrolling : DependencyObject
{
    public static bool GetIsEnabled(DependencyObject obj)
    {
        return (bool)obj.GetValue(IsEnabledProperty);
    }

    public static void SetIsEnabled(DependencyObject obj, bool value)
    {
        obj.SetValue(IsEnabledProperty, value);
    }

    public bool IsEnabled
    {
        get { return (bool)GetValue(IsEnabledProperty); }
        set { SetValue(IsEnabledProperty, value); }
    }

    public static readonly DependencyProperty IsEnabledProperty =
        DependencyProperty.RegisterAttached("IsEnabled", typeof(bool), typeof(TouchScrolling), new UIPropertyMetadata(false, IsEnabledChanged));

    static Dictionary<object, MouseCapture> _captures = new Dictionary<object, MouseCapture>();

    static void IsEnabledChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var target = d as ScrollViewer;
        if (target == null) return;

        if ((bool)e.NewValue)
        {
            target.Loaded += target_Loaded;
        }
        else
        {
            target_Unloaded(target, new RoutedEventArgs());
        }
    }

    static void target_Unloaded(object sender, RoutedEventArgs e)
    {
        System.Diagnostics.Debug.WriteLine("Target Unloaded");

        var target = sender as ScrollViewer;
        if (target == null) return;

        _captures.Remove(sender);

        target.Loaded -= target_Loaded;
        target.Unloaded -= target_Unloaded;
        target.PreviewMouseLeftButtonDown -= target_PreviewMouseLeftButtonDown;
        target.PreviewMouseMove -= target_PreviewMouseMove;

        target.PreviewMouseLeftButtonUp -= target_PreviewMouseLeftButtonUp;
    }

    static void target_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        var target = sender as ScrollViewer;
        if (target == null) return;

        _captures[sender] = new MouseCapture
        {
            VerticalOffset = target.VerticalOffset,
            Point = e.GetPosition(target),
        };
    }

    static void target_Loaded(object sender, RoutedEventArgs e)
    {
        var target = sender as ScrollViewer;
        if (target == null) return;

        System.Diagnostics.Debug.WriteLine("Target Loaded");

        target.Unloaded += target_Unloaded;
        target.PreviewMouseLeftButtonDown += target_PreviewMouseLeftButtonDown;
        target.PreviewMouseMove += target_PreviewMouseMove;

        target.PreviewMouseLeftButtonUp += target_PreviewMouseLeftButtonUp;
    }

    static void target_PreviewMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
    {
        var target = sender as ScrollViewer;
        if (target == null) return;

        target.ReleaseMouseCapture();
    }

    static void target_PreviewMouseMove(object sender, MouseEventArgs e)
    {
        if (!_captures.ContainsKey(sender)) return;

        if (e.LeftButton != MouseButtonState.Pressed)
        {
            _captures.Remove(sender);
            return;
        }

        var target = sender as ScrollViewer;
        if (target == null) return;

        var capture = _captures[sender];

        var point = e.GetPosition(target);

        var dy = point.Y - capture.Point.Y;
        if (Math.Abs(dy) > 5)
        {
            target.CaptureMouse();
        }

        target.ScrollToVerticalOffset(capture.VerticalOffset - dy);
    }

    internal class MouseCapture
    {
        public Double VerticalOffset { get; set; }
        public Point Point { get; set; }
    }

}

}

There are some quirks here. I noticed that the ScrollViewer was actually being loaded, unloaded and loaded again when the content was shown.

这里有一些怪癖。我注意到在显示内容时实际上正在加载、卸载和再次加载 ScrollViewer。

That meant that I couldn't just hook up the events in the IsEnabledChangedmethod and unhook them in the target_Unloadedevent handler, because they were being unhooked immediately. Instead, I've had to hook them up in a handler for the Loaded event, which in turn never gets unhooked.

这意味着我不能只是在IsEnabledChanged方法中连接target_Unloaded事件并在事件处理程序中取消它们，因为它们会立即被取消。相反，我不得不将它们挂接到 Loaded 事件的处理程序中，而后者永远不会解开。

That means that there's something of a "memory leak" in there, but it's one I'm prepared to live with.

这意味着那里存在某种“内存泄漏”，但我已准备好接受它。