Question

I would like to implement a drag&drop operation from TextBox to another control.
The problem is that when you select some part of text and then click on the TextBox text is deselected. Therefore when I perform DoDragDrop in MouseDown event the textBox.SelectedText is already empty.

Is there any way to avoid such behavior? I found following example but I don’t want to loose the possibility to drag&drop only a part of text.

Answer 1

I found solution. You need to inherit TextBox and override OnMouseDown and WndProc:

public class DragTextBox : TextBox
{
    private string dragText;
    private const int WM_LBUTTONDOWN = 0x201;

    protected override void OnMouseDown(MouseEventArgs e)
    {
        if (dragText.Length > 0)
        {
            SelectionStart = Text.IndexOf(dragText);
            SelectionLength = dragText.Length;
            DoDragDrop(dragText, DragDropEffects.Copy);
            SelectionLength = 0;
        }
        base.OnMouseDown(e);
    }

    protected override void WndProc(ref Message m)
    {
        if ((m.Msg == WM_LBUTTONDOWN))
            dragText = SelectedText;
        base.WndProc(ref m);
    }
}

Original code author post here