C#内TextBox的Drog&Drop拖放操作

public class DropData
{
   public string _text;
   public int _start;
   public int _len;
   
   public DropData(string text, int start, int len)
   {
      _text = text;
      _start = start;
      _len = len;
   }
}

private void textBox1_MouseUp(object sender, MouseEventArgs e)
{
   if (textBox1.SelectedText != "")
   {
      DropData d = new DropData(textBox1.SelectedText, textBox1.SelectionStart, textBox1.SelectionLength);
      textBox1.Tag = d;
   }
}

private void textBox1_MouseDown(object sender, MouseEventArgs e)
{
   if (textBox1.Tag == null) return;
   
   if (textBox1.Tag is DropData)
   {
      DropData d = textBox1.Tag as DropData;
      textBox1.SelectionStart = d._start;
      textBox1.SelectionLength = d._len;
      
      textBox1.DoDragDrop(d._text, DragDropEffects.Copy);
   }
   
   textBox1.Tag = null; //注意，这里要还原变量，否则无休止托放
}