Implement Drag-Drop in Winforms using Treeview & Split Controls

Question

I have a form that has 2 splitters. One splitter splits the form horizonally into 2 columns. The other splits the left column into 2 rows.

On the left hand column, top "row" I have a treeview. On the right hand column, I have a image viewer.

I want to drop a treeview node onto the image viewer and do something with it.

The viewer is called "viewer". The treeview is called "EntityTreeView"

The code is as follows:

 private void viewer_DragEnter(object sender, DragEventArgs e)
    {
        e.Effect = DragDropEffects.Move;
    }

    private void viewer_DragDrop(object sender, DragEventArgs e)
    {
        TreeNode droppedNode;
        droppedNode = (TreeNode)e.Data.GetData("System.Windows.Forms.TreeNode");
        MessageBox.Show(String.Format("You dropped a node with text: {0}\n on the viewer at X:{1} Y:{2}", droppedNode.Text, e.X, e.Y), "Drag Drop Finished", MessageBoxButtons.OK, MessageBoxIcon.Information);
    }

    private void EntityTreeView_ItemDrag(object sender, ItemDragEventArgs e)
    {
        DoDragDrop(e.Item, DragDropEffects.Move);

    }

    private void EntityTreeView_DragDrop(object sender, DragEventArgs e)
    {
        e.Effect = DragDropEffects.Move;
    }


    private void EntityTreeView_DragEnter(object sender, DragEventArgs e)
    {
        e.Effect = DragDropEffects.None;
    }

However, whenever I grab a treeview node and start dragging it, it immediately shows the "No" icon (i.e., the no smoking sign.. circle with a slash, whatever that's called).

Any idea what I'm doing wrong?

Thanks in advance for any help.

Answer 1

You need to set the e.Effect in the DragEnter event to DragDropEffects.Move

private void EntityTreeView_DragEnter(object sender, DragEventArgs e)
{
    e.Effect = DragDropEffects.Move    
}

Answer 2

Your code looks fine so far. What you need to do is set the AllowDrop property on "viewer" to true.