OLE Drag and Drop

Built-in Drag and Drop

A DiagramView can accept dragged shapes or nodes from ShapeListBox and NodeListView controls. To enable that, set its AllowDrop property to true. The view responds to Shape objects dragged from ShapeListBox by creating a ShapeNode at the drop position and setting its Shape property. Nodes dragged from NodeListView are cloned and the copies are added to the diagram.

Custom Drop Handling

DiagramView inherits standard drag-and-drop events from its base Control class. You could handle them to e.g. create nodes from dropped data, or to copy the data to existing node's fields. Note that you must call the ViewToDiagram method to convert the mouse position from view's to diagram's coordinate system (in MeasureUnit and according to view's ZoomFactor and Scroll position). The following example demonstrates that:

C#

void OnDiagramDragDrop(object sender, DragEventArgs e)
{
    var position = e.GetPosition(diagramView);
    position = diagramView.ViewToDiagram(position);

    var node = diagram.GetNodeAt(position);
    if (node == null)
    {
        node = diagram.Factory.CreateShapeNode(
            position.X - nodeSize.Width / 2,
            position.Y - nodeSize.Height / 2,
            nodeSize.Width, nodeSize.Height);
    }

    node.Text = (string)e.Data.GetData(typeof(string));

    e.Effects = DragDropEffects.Copy;
    e.Handled = true;
}

Size nodeSize = new Size(96, 64);

Initiate Drag Operation

You can start a drag-and-drop operation from the Diagram by calling WPF's standard DoDragDrop method. Depending on the context from which you start dragging, you might also need to cancel view's internal user interaction handling. The following example demonstrates how to drag node's text when Shift is pressed down.

C#

protected override void OnPreviewMouseDown(MouseButtonEventArgs e)
{
    if ((Keyboard.Modifiers & ModifierKeys.Shift) != 0)
    {
        var mousePosition = e.GetPosition(diagramView);
        mousePosition = diagramView.ViewToDiagram(mousePosition);

        var node = diagram.GetNodeAt(mousePosition);
        if (node != null)
        {
            if (diagramView.Interaction != null)
                diagramView.Interaction.CancelNow();
            DragDrop.DoDragDrop(this, node.Text, DragDropEffects.Copy);
            e.Handled = true;
        }
    }
}