implementing-wpf-dragdrop

WPF Drag and Drop Patterns

Implementing drag and drop functionality for data transfer within and between applications.

Advanced Patterns: See ADVANCED.md for visual feedback, list reordering, and custom data formats.

1. Drag and Drop Overview

Drag Source                           Drop Target
    │                                      │
    ├─ MouseDown                           │
    ├─ MouseMove (drag threshold)          │
    ├─ DragDrop.DoDragDrop()───────────────┤
    │                                      ├─ DragEnter
    │                                      ├─ DragOver
    │                                      ├─ DragLeave
    │                                      └─ Drop
    └─ GiveFeedback (cursor change)

2. Basic Drag Source

2.1 Simple Text Drag

namespace MyApp.Views;

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

public partial class DragSourceView : UserControl
{
    private Point _startPoint;

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

    private void TextBlock_MouseMove(object sender, MouseEventArgs e)
    {
        if (e.LeftButton != MouseButtonState.Pressed)
            return;

        var currentPoint = e.GetPosition(null);
        var diff = _startPoint - currentPoint;

        // Check if drag threshold is exceeded
        if (Math.Abs(diff.X) > SystemParameters.MinimumHorizontalDragDistance ||
            Math.Abs(diff.Y) > SystemParameters.MinimumVerticalDragDistance)
        {
            if (sender is TextBlock textBlock)
            {
                // Create data object and start drag
                var data = new DataObject(DataFormats.Text, textBlock.Text);
                DragDrop.DoDragDrop(textBlock, data, DragDropEffects.Copy);
            }
        }
    }
}

2.2 Multiple Data Formats

private void StartDragWithMultipleFormats(FrameworkElement source, object item)
{
    var data = new DataObject();

    // Add multiple formats for compatibility
    if (item is MyDataItem dataItem)
    {
        data.SetData(typeof(MyDataItem), dataItem);
        data.SetData(DataFormats.Text, dataItem.ToString());
        data.SetData(DataFormats.Serializable, dataItem);
    }

    DragDrop.DoDragDrop(source, data, DragDropEffects.Copy | DragDropEffects.Move);
}