DragDrop in TreeView

When I started on Drag and Drop in C# I could not find much on the net and so I have decided to tackle the problem here. First follow the steps to see the working sample.

1. Create a new C sharp windows application. Rename Form1 to a suitable name. I would refer it as TestForm
2. Add a treeview control with some dummy nodes randomly.
3. Extract DragDropTreeView.cs from the attached zipped file and copy DragDropTreeView.cs to the project directory.
4. Add DragDropTreeView.cs as an Existing item to the project
5. Go to TestForm.Designer.cs
6. Add

Code:

using DragDropTreeSample;

at the top of the file.
7. Now find

Code:

private System.Windows.Forms.TreeView treeView1;

and replace with

Code:

private DragDropTreeView treeView1;

8. Go to InitializeComponent function and find

Code:

this.treeView1 = new System.Windows.Forms.TreeView();

and replace with

Code:

this.treeView1 = new DragDropTreeView();

Thats it. Simple isnt it. All done and now you will see that your tree view control has the drag and drop facility with the nodes you have added. Use Ctrl Key to copy a node or move the nodes in the tree using mouse drag.

Now the question comes is what is in DragDropTreeView.cs so that it behaves in such a fashion.

First thing that it does is sets the property AllowDrop of the DragDropTreeView to true so that we can handle the drag drop events for the TreeView control.

Next it overrides the 3 basic or you can say minimal drag drop event handler of TreeView. i.e. OnDragDrop, OnDragOver, OnItemDrag

Code:

protected override void OnItemDrag(ItemDragEventArgs e)
{
	srcNodeForDrag = (TreeNode)e.Item;
	this.DoDragDrop(e.Item, DragDropEffects.All);
}

When any item is dragged we store the source node so that we can operate on the node and then start the DragDrop operation.

Code:

protected override void OnDragOver(DragEventArgs e)
{
    if ((e.KeyState & 8) == 8 &&
        (e.AllowedEffect & DragDropEffects.Copy) == DragDropEffects.Copy)
    {
        // CTL KeyState for copy.
        e.Effect = DragDropEffects.Copy;
    }
    else if ((e.AllowedEffect & DragDropEffects.Move) == DragDropEffects.Move)
    {
        e.Effect = DragDropEffects.Move;
    }
}

When any item is drag over other item we check the keyboard if we CTRL is pressed we set the copy mode of the nodes or else its the move mode.

Code:

protected override void OnDragDrop(DragEventArgs e)
{
    Point pt = PointToClient(new Point(e.X, e.Y));
    TreeNode DestinationNode = this.GetNodeAt(pt);

    // Ensure that the list item index is contained in the data.
    if (e.Data.GetDataPresent(typeof(TreeNode)))
    {
        // Perform drag-and-drop, depending upon the effect.
        if (e.Effect == DragDropEffects.Copy)
        {
            TreeNode tmpTN = (TreeNode)srcNodeForDrag.Clone();
            DestinationNode.Nodes.Add(tmpTN);
        }
        else if (e.Effect == DragDropEffects.Move)
        {
            TreeNode tmpTN = (TreeNode)srcNodeForDrag.Clone();
            DestinationNode.Nodes.Add(tmpTN);
            srcNodeForDrag.Remove();
        }
    }
}

Here we check the Data type of the drop element and depending on the operation in the drag over we copy/move the node at the destination node.

 

Do you mean you need to add the node as its siblings to the node where the drop has taken place.

If thats the case modify OnDragDrop to find the parent node of the DestinationNode and add it to the child of the parent node.

 

After you get the parent where you would like to add node you can do that easily. Just try it out.

The above case also applies to the nodes to move using the menu or something similar.

 

You need to move the node to the needed position as Add does not have any overloaded which can add a specified position of the parent node.

 

Its definitely possible. Override the paint and paint the node using different color

 

Which file you are trying to save??

 

You need to provide some more details about the xml file so that we can understand how you are reading/writing and why the changes are not happening.

Regarding scrolling while you are dragging it should work with the mouse and not with the mouse scroll as with any other normal window/controls.

 

Regarding scrolling it should be behaving as any other normal window tree view does as we dont handle or interrupt anything in the tree view.