WPF DragDrop 例子

以下是一个简单的 WPF DragDrop 例子：

XAML 代码：

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <StackPanel Orientation="Horizontal" Margin="10">
            <TextBlock Text="Drag me:" Margin="0,0,10,0" />
            <TextBlock Text="Hello, world!" Background="LightGray" Width="100" Height="50"
                       PreviewMouseLeftButtonDown="TextBlock_PreviewMouseLeftButtonDown"
                       PreviewMouseMove="TextBlock_PreviewMouseMove"
                       PreviewMouseLeftButtonUp="TextBlock_PreviewMouseLeftButtonUp" />
        </StackPanel>
        <StackPanel Orientation="Horizontal" Margin="10">
            <TextBlock Text="Drop here:" Margin="0,0,10,0" />
            <Border BorderBrush="Black" BorderThickness="1" Width="100" Height="50"
                    AllowDrop="True" Drop="Border_Drop" />
        </StackPanel>
    </Grid>
</Window>

C# 代码：

using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;

namespace WpfApp1
{
    public partial class MainWindow : Window
    {
        private bool isDragging = false;
        private Point startPoint;

        public MainWindow()
        {
            InitializeComponent();
        }

        private void TextBlock_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            startPoint = e.GetPosition(null);
            isDragging = true;
        }

        private void TextBlock_PreviewMouseMove(object sender, MouseEventArgs e)
        {
            if (isDragging && e.LeftButton == MouseButtonState.Pressed)
            {
                Point position = e.GetPosition(null);
                Vector offset = startPoint - position;

                if (Math.Abs(offset.X) > SystemParameters.MinimumHorizontalDragDistance ||
                    Math.Abs(offset.Y) > SystemParameters.MinimumVerticalDragDistance)
                {
                    DataObject data = new DataObject("myFormat", "Hello, world!");
                    DragDrop.DoDragDrop((DependencyObject)sender, data, DragDropEffects.Copy);
                    isDragging = false;
                }
            }
        }

        private void TextBlock_PreviewMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
        {
            isDragging = false;
        }

        private void Border_Drop(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent("myFormat"))
            {
                string text = (string)e.Data.GetData("myFormat");
                ((Border)sender).Child = new TextBlock { Text = text, Background = Brushes.LightGray };
            }
        }
    }
}

这个例子演示了如何在 WPF 中实现拖放操作。我们创建了一个包含两个 StackPanel 的 Window，第一个 StackPanel 包含一个 TextBlock，可以被拖动，第二个 StackPanel 包含一个 Border，可以接受拖放操作。当用户按下鼠标左键并移动 TextBlock 时，如果移动距离超过一定阈值，就会触发拖放操作。在拖放操作中，我们将一个字符串放入 DataObject 中，并指定数据格式为 "myFormat"。在 Border 的 Drop 事件中，我们检查数据格式是否为 "myFormat"，如果是，就将字符串显示在 Border 中。