The following code example demonstrates a drag-and-drop operation between two ListBox controls. The example calls the DoDragDrop method when the drag action starts. The drag action starts if the mouse has moved more than SystemInformation..::.DragSize from the mouse location during the MouseDown event. The IndexFromPoint method is used to determine the index of the item to drag during the MouseDown event.
The example also demonstrates using custom cursors for the drag-and-drop operation. The example requires that two cursor files, 3dwarro.cur and 3dwno.cur, exist in the application directory, for the custom drag and no-drop cursors, respectively. The custom cursors will be used if the UseCustomCursorsCheck CheckBox is checked. The custom cursors are set in the GiveFeedback event handler.
The keyboard state is evaluated in the DragOver event handler for the right ListBox, to determine what the drag operation will be based on state of the SHIFT, CTRL, ALT, or CTRL+ALT keys. The location in the ListBox where the drop would occur is also determined during the DragOver event. If the data to drop is not a String, then the DragEventArgs..::.Effect is set to a value of None in DragDropEffects. Finally, the status of the drop is displayed in the DropLocationLabel Label.
The data to drop for the right ListBox is determined in the DragDrop event handler and the String value is added at the appropriate place in the ListBox. If the drag operation moves outside the bounds of the form, then the drag-and-drop operation is canceled in the QueryContinueDrag event handler.
This code excerpt demonstrates using the DragDrop event. See the DoDragDrop method for the complete code example.
Private Sub ListDragTarget_DragDrop(ByVal sender As Object, ByVal e As DragEventArgs) Handles ListDragTarget.DragDrop
' Ensures that the list item index is contained in the data.
If (e.Data.GetDataPresent(GetType(System.String))) Then
Dim item As Object = CType(e.Data.GetData(GetType(System.String)), System.Object)
' Perform drag-and-drop, depending upon the effect.
If (e.Effect = DragDropEffects.Copy Or _
e.Effect = DragDropEffects.Move) Then
' Insert the item.
If (indexOfItemUnderMouseToDrop <> ListBox.NoMatches) Then
ListDragTarget.Items.Insert(indexOfItemUnderMouseToDrop, item)
Else
ListDragTarget.Items.Add(item)
End If
End If
' Reset the label text.
DropLocationLabel.Text = "None"
End If
End Sub
private void ListDragTarget_DragDrop(object sender, System.Windows.Forms.DragEventArgs e)
{
// Ensure that the list item index is contained in the data.
if (e.Data.GetDataPresent(typeof(System.String))) {
Object item = (object)e.Data.GetData(typeof(System.String));
// Perform drag-and-drop, depending upon the effect.
if (e.Effect == DragDropEffects.Copy ||
e.Effect == DragDropEffects.Move) {
// Insert the item.
if (indexOfItemUnderMouseToDrop != ListBox.NoMatches)
ListDragTarget.Items.Insert(indexOfItemUnderMouseToDrop, item);
else
ListDragTarget.Items.Add(item);
}
}
// Reset the label text.
DropLocationLabel.Text = "None";
}
void ListDragTarget_DragDrop( Object^ /*sender*/, System::Windows::Forms::DragEventArgs^ e )
{
// Ensure that the list item index is contained in the data.
if ( e->Data->GetDataPresent( System::String::typeid ) )
{
Object^ item = dynamic_cast<Object^>(e->Data->GetData( System::String::typeid ));
// Perform drag-and-drop, depending upon the effect.
if ( e->Effect == DragDropEffects::Copy || e->Effect == DragDropEffects::Move )
{
// Insert the item.
if ( indexOfItemUnderMouseToDrop != ListBox::NoMatches )
ListDragTarget->Items->Insert( indexOfItemUnderMouseToDrop, item );
else
ListDragTarget->Items->Add( item );
}
}
// Reset the label text.
DropLocationLabel->Text = "None";
}