Drag-and-Drop Operation in Windows Forms

Drag-and-Drop Operation in Windows Forms

To perform drag-and-drop operations within Windows-based applications you must handle a series of events, most notably the DragEnter, DragLeave, and DragDrop events. By working with the information available in the event arguments of these events, you can easily facilitate drag-and-drop operations.

To Start The Drag Operation

All drag-and-drop operations begin with dragging. The functionality to enable data to be collected when dragging begins is implemented in the DoDragDrop method.

In the following example, the MouseDown event is used to start the drag operation because it is the most intuitive (most drag-and-drop actions begin with the mouse button being depressed). However, remember that any event could be used to initiate a drag-and-drop procedure.

• In the MouseDown event for the control where the drag will begin, use the DoDragDrop method to set the data to be dragged and the allowed effect dragging will have. For more information, see Data and AllowedEffect.
• The following example shows how to initiate a drag operation. The control where the drag begins is a Button control, the data being dragged is the string representing the Text property of the Button control, and the allowed effects are either copying or moving.

private void button1_MouseDown(object sender, 
System.Windows.Forms.MouseEventArgs e)
{
   button1.DoDragDrop(button1.Text, DragDropEffects.Copy | 
      DragDropEffects.Move);
}

To perform a drop



Once you have begun dragging data from a location on a Windows Form or control, you will naturally want to drop it somewhere. The cursor will change when it crosses an area of a form or control that is correctly configured for dropping data. Any area within a Windows Form or control can be made to accept dropped data by setting the AllowDrop property and handling the DragEnter and DragDrop events.






Set the AllowDrop property to true.


In the DragEnter event for the control where the drop will occur, ensure that the data being dragged is of an acceptable type (in this case, Text). The code then sets the effect that will happen when the drop occurs to a value in the DragDropEffects enumeration. 







private void textBox1_DragEnter(object sender, 
System.Windows.Forms.DragEventArgs e)
{
   if (e.Data.GetDataPresent(DataFormats.Text)) 
      e.Effect = DragDropEffects.Copy;
   else
      e.Effect = DragDropEffects.None;
}

In the DragDrop event for the control where the drop will occur, use the GetData method to retrieve the data being dragged.

In the example below, a TextBox control is the control being dragged to (where the drop will occur). The code sets the Text property of the TextBox control equal to the data being dragged.
private void textBox1_DragDrop(object sender, 
System.Windows.Forms.DragEventArgs e)
{
   textBox1.Text = e.Data.GetData(DataFormats.Text).ToString();
}