不能让简单的WPF拖放工作

问题描述

对于一个简单的测试，我想将一个Button拖到一个TextBox。我可以开始拖动Button，但是Drop事件没有被提出。我缺少什么？

For a simple test I want to drag a Button to a TextBox. I can start dragging the Button, but the Drop event is not raised. What am I missing?

Xaml：

<Window x:Class="DayPlanner.View.DnDTest"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="DnDTest" Height="200" Width="200">
    <StackPanel>
        <Button Name="button" 
                Content="OK" 
                PreviewMouseLeftButtonDown="button_PreviewMouseLeftButtonDown" 
                PreviewMouseMove="button_PreviewMouseMove"/>
        <TextBox Name="textBox"
                 AllowDrop="True"
                 DragEnter="textBox_DragEnter"
                 Drop="textBox_Drop"/>
    </StackPanel>
</Window>

代码：

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

    private Point dragStartPoint;

    private void button_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        dragStartPoint = e.GetPosition(null);
    }

    private static bool IsDragging(Point dragStartPoint, MouseEventArgs e)
    {
        var diff = e.GetPosition(null) - dragStartPoint;
        return
            e.LeftButton == MouseButtonState.Pressed &&
            (Math.Abs(diff.X) > SystemParameters.MinimumHorizontalDragDistance ||
                Math.Abs(diff.Y) > SystemParameters.MinimumVerticalDragDistance);
    }

    private void button_PreviewMouseMove(object sender, MouseEventArgs e)
    {
        if (IsDragging(dragStartPoint, e))
        {
            DragDrop.DoDragDrop(button, new DataObject("Button", button), DragDropEffects.Move);
            e.Handled = true;
        }
    }

    private void textBox_DragEnter(object sender, DragEventArgs e)
    {
        e.Handled = true;
    }

    private void textBox_Drop(object sender, DragEventArgs e)
    {
        var button = (Button)e.Data.GetData("Button");
        textBox.Text = string.Format("[0]", button.Content.ToString());
        e.Handled = true;
    }
}

推荐答案

可能是一些奇怪的情况，但要解决它，我需要处理或拖动事件，包括预览版本。

This might be some strange case, but to fix it, I needed to handle or dragging events, including the Preview versions.

这是如何使其工作。

Xaml：

<Window x:Class="DayPlanner.View.DnDTestBasic"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="DnDTestBasic" Height="200" Width="200">
    <StackPanel>
        <Button Name="button" 
                Content="OK" 
                PreviewMouseLeftButtonDown="button_PreviewMouseLeftButtonDown" 
                PreviewMouseMove="button_PreviewMouseMove"/>
        <TextBox Name="textBox"
                 AllowDrop="True"
                 PreviewDragEnter="textBox_Dragging"
                 DragEnter="textBox_Dragging"
                 PreviewDragOver="textBox_Dragging"
                 DragOver="textBox_Dragging"
                 Drop="textBox_Drop"/>
        <TextBlock Name="status"
                   Text="No dragging"/>
    </StackPanel>
</Window>

代码：

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

    private Point dragStartPoint;

    private void button_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        dragStartPoint = e.GetPosition(null);
        status.Text = "New drag start position";
    }

    private static bool IsDragging(Point dragStartPoint, MouseEventArgs e)
    {
        var diff = e.GetPosition(null) - dragStartPoint;
        return
            e.LeftButton == MouseButtonState.Pressed &&
            (Math.Abs(diff.X) > SystemParameters.MinimumHorizontalDragDistance ||
             Math.Abs(diff.Y) > SystemParameters.MinimumVerticalDragDistance);
    }

    private void button_PreviewMouseMove(object sender, MouseEventArgs e)
    {
        if (IsDragging(dragStartPoint, e))
        {
            status.Text = "Starting drag...";
            DragDrop.DoDragDrop(button, new DataObject("Button", button), DragDropEffects.Copy);
            status.Text = "Dragging done.";
            e.Handled = true;
        }
    }

    private void textBox_Dragging(object sender, DragEventArgs e)
    {
        if (e.Data.GetDataPresent("Button"))
            e.Effects = DragDropEffects.Copy;
        else
            e.Effects = DragDropEffects.None;
        e.Handled = true;
    }

    private void textBox_Drop(object sender, DragEventArgs e)
    {
        var button = (Button)e.Data.GetData("Button");
        textBox.Text = string.Format("[{0}]", button.Content.ToString());
        e.Handled = true;
    }
}

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