WPF拖放一个按钮 [英] WPF drag and drop on a button

问题描述

我正在写有按钮的网格WPF应用程序，我想允许用户拖放网格之间的按钮，可能是应用程序的不同实例之间。我试着通过添加一个处理程序按钮上的previewMouseMove事件，然后调用的DoDragDrop如果左边鼠标按键时这样做，但是当我拖放按钮，它总是结束调用的DoDragDrop两次，降事件处理程序的两倍。有谁知道为什么出现这种情况，如何prevent呢？

I'm writing a WPF application that has grids of buttons and I want to allow the user to drag and drop buttons between grids, possibly between different instances of the application. I've tried doing this by adding a handler to the PreviewMouseMove event on the button and then calling DoDragDrop if the left mouse button is down, but when I drag and drop the button it always ends up calling DoDragDrop twice and the drop event handler twice. Does anyone know why this happens and how to prevent it?

下面是这表明了问题的一些例子XAML：

Here's some example XAML which demonstrates the problem:

<Window x:Class="WpfTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <DockPanel>
        <Button PreviewMouseMove="PreviewMouseMove" x:Name="m_button" Width="250">
            Hello, world!
        </Button>
        <Label Drop="Drop" AllowDrop="True">
            Drop here!
        </Label>
    </DockPanel>
</Window>

和相应的code：

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void PreviewMouseMove(object sender, MouseEventArgs e)
    {
        if (e.LeftButton == MouseButtonState.Pressed)
        {
            ++m_dragIndex;
            System.Console.WriteLine("Dragged: " + m_dragIndex.ToString());
            DragDrop.DoDragDrop(m_button, m_dragIndex, DragDropEffects.All);
            e.Handled = true;
        }
    }

    private void Drop(object sender, DragEventArgs e)
    {
        System.Console.WriteLine("Dropped: " + e.Data.GetData(typeof(Int32)).ToString());
    }

    private int m_dragIndex;
}

对于单拖，这被写入到输出：

For a single drag, this gets written to the output:

Dragged: 1
Dragged: 2
Dropped: 2
Dropped: 1

更新：我已经改变了例如code以上，以显示其下降当按钮被丢弃到的东西的事件被调用

UPDATE: I've changed the example code above to show which drop events get called when the button is dropped onto something.

更新：更新的问题，包括容器和应用程序实例之间拖动，因为这是使用的DragDrop系统的激励因素。

UPDATE: Updated the question to include dragging between containers and application instances, since this is the motivating factor for using the DragDrop system.

推荐答案

我已经找到了解决方法这一点 - 因为第一次的DoDragDrop内部调用第二previewMouseMove，我可以跟踪我是否已经是$内p $ pviewMouseMove呼叫，忽略它，如果我。这似乎有点讨厌，虽然所以我希望有一个更好的解决方案。

I've found a workaround for this - since the first DoDragDrop calls the second PreviewMouseMove internally, I can track whether I'm already inside a PreviewMouseMove call and ignore it if I am. This seems a bit nasty though so I'm hoping there's a better solution.

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void PreviewMouseMove(object sender, MouseEventArgs e)
    {
        if(!m_inMouseMove)
        {
            m_inMouseMove = true;
            if (e.LeftButton == MouseButtonState.Pressed)
            {
                ++m_dragIndex;
                System.Console.WriteLine("Dragged: " + m_dragIndex.ToString());
                DragDrop.DoDragDrop(m_button, m_dragIndex, DragDropEffects.All);
                e.Handled = true;
            }
            m_inMouseMove = false;
        }
    }

    private void Drop(object sender, DragEventArgs e)
    {
        System.Console.WriteLine("Dropped: " + e.Data.GetData(typeof(Int32)).ToString());
    }

    private int m_dragIndex;
    bool m_inMouseMove;
}

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