Drag & Drop in Windows Forms

[jmcilhinney]

VB version here.

I'm sure others have posted about this topic before but I'm sure another won't hurt. I'll post various examples of drag & drop within the same control, between controls and between applications.

If you're interested in performing drag & drop operations in WinForms then I suggest that you read this and this at least.

I'll start with moving items between two ListBoxes, which is relatively simple.

1. Create a new WinForms application project.
2. Add two ListBoxes to the form.
3. Replace the existing form code with the following:

public Form1()
{
    InitializeComponent();

    // Hook up the form event handler.
    this.Load += new EventHandler(Form1_Load);
}

private void Form1_Load(object sender, EventArgs e)
{
    // Allow data to be dropped on both ListBoxes.
    this.listBox1.AllowDrop = true;
    this.listBox2.AllowDrop = true;

    // Populate the ListBoxes.
    this.listBox1.Items.AddRange(new string[] {"List 1, Item 1",
                                               "List 1, Item 2",
                                               "List 1, Item 3",
                                               "List 1, Item 4",
                                               "List 1, Item 5"});
    this.listBox2.Items.AddRange(new string[] {"List 2, Item 1",
                                               "List 2, Item 2",
                                               "List 2, Item 3",
                                               "List 2, Item 4",
                                               "List 2, Item 5"});

    // Hook up the ListBox event handlers.
    this.listBox1.MouseDown += new MouseEventHandler(ListBox_MouseDown);
    this.listBox2.MouseDown += new MouseEventHandler(ListBox_MouseDown);
    this.listBox1.DragEnter += new DragEventHandler(ListBox_DragEnter);
    this.listBox2.DragEnter += new DragEventHandler(ListBox_DragEnter);
    this.listBox1.DragDrop += new DragEventHandler(ListBox_DragDrop);
    this.listBox2.DragDrop += new DragEventHandler(ListBox_DragDrop);
}

void ListBox_MouseDown(object sender, MouseEventArgs e)
{
    ListBox source = (ListBox)sender;

    for (int index = 0; index < source.Items.Count; index++)
    {
        // Test whether the mouse location is within an item
        if (source.GetItemRectangle(index).Contains(e.Location))
        {
            // The mouse was depressed on an item so allow a move operation.
            source.DoDragDrop(source, DragDropEffects.Move);

            break;
        }
    }
}

void ListBox_DragEnter(object sender, DragEventArgs e)
{
    ListBox source = (ListBox)sender;

    if (e.Data.GetDataPresent("System.Windows.Forms.ListBox", false) &&
        e.Data.GetData("System.Windows.Forms.ListBox", false) != source)
    {
        // The data being dragged is a ListBox but not the one that was just entered.
        e.Effect = DragDropEffects.Move;
    }
}

void ListBox_DragDrop(object sender, DragEventArgs e)
{
    ListBox source = (ListBox)sender;

    if (e.Data.GetDataPresent("System.Windows.Forms.ListBox", false))
    {
        // Get the ListBox that the data was dragged from.
        ListBox data = (ListBox)e.Data.GetData("System.Windows.Forms.ListBox", false);


        // Make sure we aren't trying to drag from and drop to the same control.
        if (data != source)
        {
            // Get the item that was dragged.
            object item = data.SelectedItem;

            // Remove the item from its original location.
            data.Items.Remove(item);

            // Get the current mouse location relative to the control being dropped on.
            Point location = source.PointToClient(new Point(e.X, e.Y));
            int dropIndex = -1;

            // Find the item over which the mouse was released.
            for (int index = 0; index < source.Items.Count; index++)
            {
                if (source.GetItemRectangle(index).Contains(location))
                {
                    dropIndex = index;

                    break;
                }
            }

            if (dropIndex == -1)
            {
                // The mouse was not released over an item so add the new item to the end.
                source.Items.Add(item);
            }
            else
            {
                // Insert the new item above the item it was dropped on.
                source.Items.Insert(dropIndex, item);
            }
        }
    }
}

4. Run the project and start dragging and dropping.

I'll refine this example and add more over time. If there's anything you specifically want to see then post a request and I'll see if I can get to it.