Question

Hail Stack!

I’m having a hard time trying to figure out why my treeview (or any other component, even the form itself) won’t fire the event DragDrop.

I’ve settled my form like this:
A Form with a Panel inside.
The Panel have a TreeView, and this TreeView (MyTree) has the following code:

MyTree.AllowDrop = true;
MyTree.DragDrop += new System.Windows.Forms.DragEventHandler(onDragDrop);
MyTree.DragEnter += new System.Windows.Forms.DragEventHandler(onDragEnter);
MyTree.DragLeave += new System.EventHandler(onDragLeave);
MyTree.DragOver += new System.Windows.Forms.DragEventHandler(onDragOver);

The handlers looks like this:

private void onDragEnter(object sender, DragEventArgs e)
{
    Console.WriteLine(" === DragEnter === ");
}

private void onDragLeave(object sender, EventArgs e)
{
    Console.WriteLine(" === DragLeave === ");
}

private void onDragOver(object sender, DragEventArgs e)
{
    Console.WriteLine(" === DragOver === ");
}

private void onDragDrop(object sender, DragEventArgs e)
{
    Console.WriteLine(" === DragDrop === ");
}

When I test my app, dragging a *.txt file (or anything) the output are something like:

=== DragEnter ===
=== DragOver ===
=== DragOver ===
...
=== DragOver ===
=== DragLeave ===

The last line ( === DragLeave === ) wasn’t meant to be a leave event.
In fact, this line is printed when I release the mouse button over my TreeView.

I’m I doing something terribly wrong?

Answer 1

You need to set e.Effect in DragOver to something other than None to tell the system that you’re willing to be dropped on.