How to: Subclass a TreeView by Using Native Callbacks

Article
2006-12-13

This example shows how to subclass a TreeView control to create a NodeMouseClick event, which is not available in the .NET Compact Framework.

The form displays the subclassed TreeView control and information about a clicked node. It shows the a node's text and the x and y coordinates of where the TreeView control was clicked, which changes as you click in different places on a node.

This example program is described in detail in Subclassing Controls with a Managed Window Procedure.

To subclass a TreeView control to create a NodeMouseClick event

In Microsoft Visual Studio 2005, create a Smart Device Pocket PC project.
Add the Win32 helper class to your project. This code is available in How to: Use a Helper Class for Platform Invokes.
Add the WinProcHooker class to your project. This code is available in How to: Use a Class for Hooking Windows Procedures.

Add the TreeViewBonus class to your project.

// Extends the standard TreeView control to add an implementation
// of the NodeMouseClick event.
public class TreeViewBonus : TreeView
{
    // The original parent of this control.
    Control prevParent = null;

    // Creates a new instance of the derived TreeView control
    public TreeViewBonus()
    {
    }

    // Called when the control's parent is changed. Here we hook into that
    // parent's WndProc and spy on the WM_NOTIFY message. When the parent
    // changes, we unhook the old parent's WndProc and hook into the new one.
    protected override void OnParentChanged(EventArgs e)
    {
        // unhook the old parent
        if (this.prevParent != null)
        {
            WndProcHooker.UnhookWndProc(prevParent, Win32.WM_NOTIFY);
        }
        // update the previous parent
        prevParent = this.Parent;

        // hook up the new parent
        if (this.Parent != null)
        {
            WndProcHooker.HookWndProc(this.Parent,
            new WndProcHooker.WndProcCallback(this.WM_Notify_Handler),
            Win32.WM_NOTIFY);
        }

        base.OnParentChanged(e);
    }

    // Occurs when the user clicks a TreeNode with the mouse.
    public event TreeNodeMouseClickEventHandler NodeMouseClick;

    // Occurs when the mouse pointer is over the control and a mouse button is clicked.
    protected void OnNodeMouseClick(TreeNodeMouseClickEventArgs e)
    {
        if (NodeMouseClick != null)
            NodeMouseClick(this, e);
   }

    // The method that gets called when a WM_NOTIFY message is received by the
    // TreeView's parent.
    // hwnd - The handle of the window that received the message
    // msg - The message received
    // wParam - The wParam arguments for the message
    // lParam - The lParam arguments for the message
    // handled - Set to true to indicate that this message was handled
    // Returns an appropriate return code for the message handled
    int WM_Notify_Handler(
        IntPtr hwnd, uint msg, uint wParam, int lParam,
        ref bool handled)
    {
        Win32.NMHDR nmHdr = new Win32.NMHDR();
        System.Runtime.InteropServices.Marshal.PtrToStructure((IntPtr)lParam, nmHdr);
        switch (nmHdr.code)
        {
            case Win32.NM_RCLICK:
            case Win32.NM_CLICK:
                // get the cursor coordinates on the client
                Point msgPos = Win32.LParamToPoint((int)Win32.GetMessagePos());
                msgPos = this.PointToClient(msgPos);

                // check to see if the click was on an item
                Win32.TVHITTESTINFO hti = new Win32.TVHITTESTINFO();
                hti.pt.X = msgPos.X;
                hti.pt.Y = msgPos.Y;
                int hitem = Win32.SendMessage(this.Handle, Win32.TVM_HITTEST, 0, ref hti);
                uint htMask = (
                    Win32.TVHT_ONITEMICON |
                    Win32.TVHT_ONITEMLABEL |
                    Win32.TVHT_ONITEMINDENT |
                    Win32.TVHT_ONITEMBUTTON |
                    Win32.TVHT_ONITEMRIGHT |
                    Win32.TVHT_ONITEMSTATEICON);
                if ((hti.flags & htMask) != 0)
                {
                    bool leftButton = (nmHdr.code == Win32.NM_CLICK);
                    RaiseNodeMouseClickEvent(hti.hItem,
                        leftButton ? MouseButtons.Left : MouseButtons.Right,
                        msgPos);
                    return 0;
                }
                break;
            default:
                break;
        }
        return 0;
    }

    // Raises the TreeNodeMouseClick event for the TreeNode with the specified handle.
    // hNode - The handle of the node for which the event is raised
    // button - The [mouse] buttons that were pressed to raise the event
    // coords - The [client] cursor coordinates at the time of the event
    void RaiseNodeMouseClickEvent(IntPtr hNode, MouseButtons button, Point coords)
    {
        TreeNode tn = FindTreeNodeFromHandle(this.Nodes, hNode);

        TreeNodeMouseClickEventArgs e = new TreeNodeMouseClickEventArgs(
            tn,
            button,
            1, coords.X, coords.Y);

        OnNodeMouseClick(e);
    }

    // Finds a TreeNode in the provided TreeNodeCollection that has the handle specified.
    // Warning: recursion!
    // tnc - The TreeNodeCollection to search
    // handle - The handle of the TreeNode to find in the collection
    // Returns tThe TreeNode if found; null otherwise
    TreeNode FindTreeNodeFromHandle(TreeNodeCollection tnc, IntPtr handle)
    {
        foreach (TreeNode tn in tnc)
        {
        if (tn.Handle == handle) return tn;
            // we couldn't have clicked on a child of this node if this node
            // is not expanded!
            if (tn.IsExpanded)
            {
                TreeNode tn2 = FindTreeNodeFromHandle(tn.Nodes, handle);
                if (tn2 != null) return tn2;
            }
        }
        return null;
    }
}

Add the TreeNodeMouseClickEventArgs class to your project.

// Provides data for the System.Windows.Forms.TreeView.NodeMouseClick event
public class TreeNodeMouseClickEventArgs : MouseEventArgs
{
    // Initializes a new instance of the TreeNodeMouseClickEventArgs class.
    // node - The node that was clicked
    // button - One of the System.Windows.Forms.MouseButtons members
    // clicks - The number of clicks that occurred
    // x - The x-coordinate where the click occurred
    // y - The y-coordinate where the click occurred
    public TreeNodeMouseClickEventArgs(TreeNode node, MouseButtons button, int clicks, int x, int y)
        :
        base(button, clicks, x, y, 0)
    {
        nodeValue = node;
    }

    //
    // Gets the node that was clicked.
    //
    public TreeNode Node
    {
        get { return nodeValue; }
        set { nodeValue = value; }
    }
    TreeNode nodeValue;

    public override string ToString()
    {
        return string.Format(
            "TreeNodeMouseClickEventArgs\r\n\tNode: {0}\r\n\tButton: {1}\r\n\tX: {2}\r\n\tY: {3}",
            nodeValue.Text, Button.ToString(), X, Y);
    }
}

Declare a form variable named treeViewB of type TreeViewBonus.
```
private TreeViewBonus treeViewB;
```

Add the following code to the constructor of the Form1 class, which should follow the call to InitializeComponent. This code also adds a range of tree nodes and arranges their hierarchy.

InitializeComponent();
this.treeViewB = new TreeViewBonus();
this.treeViewB.NodeMouseClick += new TreeNodeMouseClickEventHandler(this.tv_NodeMouseClicked);
this.treeViewB.Location = new System.Drawing.Point(18, 16);
this.treeViewB.Size = new System.Drawing.Size(205, 144);
this.treeViewB.Name = "treeViewB";


// Set up the tree nodes.
System.Windows.Forms.TreeNode treeNode1 = new System.Windows.Forms.TreeNode("Node0");
System.Windows.Forms.TreeNode treeNode2 = new System.Windows.Forms.TreeNode("Node2");
System.Windows.Forms.TreeNode treeNode3 = new System.Windows.Forms.TreeNode("Node3");
System.Windows.Forms.TreeNode treeNode4 = new System.Windows.Forms.TreeNode("Node6");
System.Windows.Forms.TreeNode treeNode5 = new System.Windows.Forms.TreeNode("Node7");
System.Windows.Forms.TreeNode treeNode6 = new System.Windows.Forms.TreeNode("Node8");
System.Windows.Forms.TreeNode treeNode7 = new System.Windows.Forms.TreeNode("Node4");
System.Windows.Forms.TreeNode treeNode8 = new System.Windows.Forms.TreeNode("Node1");
System.Windows.Forms.TreeNode treeNode9 = new System.Windows.Forms.TreeNode("Node5");
System.Windows.Forms.TreeNode treeNode10 = new System.Windows.Forms.TreeNode("Node9");
System.Windows.Forms.TreeNode treeNode11 = new System.Windows.Forms.TreeNode("Node10");
System.Windows.Forms.TreeNode treeNode12 = new System.Windows.Forms.TreeNode("Node11");

treeNode2.Text = "Node2";
treeNode4.Text = "Node6";
treeNode5.Text = "Node7";
treeNode6.Text = "Node8";
treeNode3.Nodes.AddRange(new System.Windows.Forms.TreeNode[] {
        treeNode4,
        treeNode5,
        treeNode6});
treeNode3.Text = "Node3";
treeNode7.Text = "Node4";
treeNode1.Nodes.AddRange(new System.Windows.Forms.TreeNode[] {
        treeNode2,
        treeNode3,
        treeNode7});
treeNode1.Text = "Node0";
treeNode12.Text = "Node11";
treeNode11.Nodes.AddRange(new System.Windows.Forms.TreeNode[] {
        treeNode12});
treeNode11.Text = "Node10";
treeNode10.Nodes.AddRange(new System.Windows.Forms.TreeNode[] {
        treeNode11});
treeNode10.Text = "Node9";
treeNode9.Nodes.AddRange(new System.Windows.Forms.TreeNode[] {
        treeNode10});
treeNode9.Text = "Node5";
treeNode8.Nodes.AddRange(new System.Windows.Forms.TreeNode[] {
        treeNode9});
treeNode8.Text = "Node1";
this.treeViewB.Nodes.AddRange(new System.Windows.Forms.TreeNode[] {
        treeNode1,
        treeNode8});

this.Controls.Add(treeViewB);

Add the delegate and the event-handling method for the derived NodeMouseClick event to the Form1 class.

    // Delegate represents the method that will handle
    // the NodeMouseClick event of a TreeView.
    // Parameters:
    // sender - The source of the event.
    // e - A TreeNodeMouseClickEventArgs that contains the event data.
    public delegate void TreeNodeMouseClickEventHandler(object sender, TreeNodeMouseClickEventArgs e);

private void tv_NodeMouseClicked(object sender, TreeNodeMouseClickEventArgs e)
{
    // Show the current node and the coordinates
    // in TreeView control where it was clicked.
    // This is just some of the information you
    // can obtain from TreeNodeMouseClickEventArgs.

    // Use a StringBuilder for efficient
    // use of device resources.
    StringBuilder sb = new StringBuilder();
    sb.Append(e.Node.Text + " ");
    sb.Append("X: " + e.X.ToString() + ", ");
    sb.Append("Y: " + e.Y.ToString());

    label1.Text = sb.ToString();

}

Compile and run the application.

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How to: Subclass a TreeView by Using Native Callbacks

To subclass a TreeView control to create a NodeMouseClick event

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