Editable TreeView

andreww — Fri, 25 May 2007 05:03:00 GMT

As I was updating the COM Shim Wizards (the new version should be published in a couple of weeks), I found I had a need for an editable TreeView. There is only limited support for editing in the standard TreeView. So, I did what all sensible people do – I LiveSearched for it to see if I could reuse something out there. To my surprise, there really wasn't anything (I double-checked with Google). However, I did find an article on building a better combobox, so I borrowed a couple of the techniques in that.

In the end, it turned out to be pretty simple. Obviously, you need to derive a class from TreeView, and override the WndProc so that you can hijack the messages of interest before (or instead of) the parent implementation. I wanted to trap the user double-clicking the left mouse button, and also pressing the delete key.

My requirements were pretty simple: if the user double-clicks an existing root node in the tree, I want to add a child to that node. If they double-click somewhere that's not on a root node, I want to add a new root node to the end of the tree. This scheme only supports 2 levels of node – which is exactly what I wanted for the wizard dialog – but, clearly, you could expand this to suit your own requirements. If they press Delete, I want to delete the selected node. That's it. Implementation was also pretty simple – the significant code is listed below:

public class TreeViewEx : TreeView

{

protected override void WndProc(ref Message m)

{

switch (m.Msg)

{

case (int)Win32Messages.WM_LBUTTONDBLCLK :

int x = Win32Macros.LoWord(m.LParam.ToInt32());

int y = Win32Macros.HiWord(m.LParam.ToInt32());

TreeViewHitTestInfo info = this.HitTest(x, y);

if (info.Node != null)

{

// They've clicked on a node.

TreeNode hitNode = info.Node;

// If this is a root node, add a child to it.

// Otherwise, do nothing.

if (hitNode.Level == 0)

{

hitNode = info.Node;

TreeNode newNode = hitNode.Nodes.Add("New Child Node");

this.SelectedNode = newNode;

}

else

{

// They've clicked somewhere other than a node.

// Add a root node to the end of the tree.

this.Nodes.Add("New Root Node");

}

return;

case (int)Win32Messages.WM_KEYDOWN :

// If they press Delete, we'll delete the selected node.

if (m.WParam.ToInt32() == Win32VirtualKeys.VK_DELETE)

{

if (this.SelectedNode != null)

{

this.SelectedNode.Remove();

}

return;

}

base.WndProc(ref m);

}

The above listing is my entire custom TreeView class – it doesn't get much simpler than this. You can see from this that I've also defined some helpers: Win32Messages, Win32VirtualKeys, and Win32Macros. They look like this:

public enum Win32Messages

{

// etc

WM_KEYDOWN = 0x100,

WM_KEYFIRST = 0x100,

WM_KEYLAST = 0x108,

WM_KEYUP = 0x101,

WM_LBUTTONDBLCLK = 0x203,

WM_LBUTTONDOWN = 0x201,

WM_LBUTTONUP = 0x202,

// etc

}

class Win32VirtualKeys

{

// etc

public const uint VK_INSERT = 0x2D;

public const uint VK_DELETE = 0x2E;

public const uint VK_HELP = 0x2F;

// etc

}

Of course, I got most of these from www.pinvoke.net. The macros were a bit trickier – I hacked these together from the C++ sources in windef.h, winuser.h:

public class Win32Macros

{

public static int MakeLong(int LoWord, int HiWord)

{

return (HiWord << 16) | (LoWord & 0xffff);

}

public static IntPtr MakeLParam(int LoWord, int HiWord)

{

return (IntPtr)((HiWord << 16) | (LoWord & 0xffff));

}

public static int HiWord(int Number)

{

return (Number >> 16) & 0xffff;

}

public static int LoWord(int Number)

{

return Number & 0xffff;

}

Andrew Whitechapel : Winforms

Editable TreeView