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The full framework TreeView control supports setting a Font on a per-node basis, the Compact Framework control doesn’t support this, however with a little interop magic you can mark individual nodes as Bold. Because the .NETCF v2.0 TreeView control exposes it’s own window handle, and each TreeNode also exposes it’s handle, we have all the raw data we need to format the node. First we need to define a structure and a couple of enumerations:-

internal struct TVITEM
{
public TVIF mask;
public IntPtr hItem;
public TVIS state;
public TVIS stateMask;
[System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.LPWStr)]
string pszText;
int cchTextMax;
int iImage;
int iSelectedImage;
int cChildren;
int lParam;
}

[Flags()]
internal enum TVIF
{
TEXT =0x0001,
IMAGE =0x0002,
PARAM =0x0004,
STATE =0x0008,
HANDLE =0x0010,
SELECTEDIMAGE =0x0020,
CHILDREN =0x0040,
}

[Flags()]
internal enum TVIS
{
SELECTED =0x0002,
CUT =0x0004,
DROPHILITED =0x0008,
BOLD =0x0010,
EXPANDED =0x0020,
EXPANDEDONCE =0x0040,
EXPANDPARTIAL =0x0080,

OVERLAYMASK =0x0F00,
STATEIMAGEMASK =0xF000,
USERMASK =0xF000,
}

Then I’ve created a single static method which can set the bold state of any node:-

public static void SetNodeEmphasis(TreeNode n, bool bold)
{
//get the control and node handles
IntPtr hTreeview = n.TreeView.Handle;
IntPtr hNode = n.Handle;

//create a TVITEM struct
TVITEM t = new TVITEM();
t.hItem = hNode;
//mark only the handle and state members as valid
t.mask = TVIF.HANDLE | TVIF.STATE;
//set the state to bold if bold param was true
t.state = bold ? TVIS.BOLD : 0;
//set statemask to show we want to set the bold state
t.stateMask = TVIS.BOLD;

//pin the struct in memory
GCHandle hTVITEM = GCHandle.Alloc(t, GCHandleType.Pinned);
//create a TVM_SETITEM message with the handle of our pinned struct
Microsoft.WindowsCE.Forms.Message m = Microsoft.WindowsCE.Forms.Message.Create(hTreeview, 0x113F, IntPtr.Zero, hTVITEM.AddrOfPinnedObject());
//send the message to the treeview
Microsoft.WindowsCE.Forms.MessageWindow.SendMessage(ref m);
//free the pinned structure
hTVITEM.Free();
}

The method is easy to reuse as you only need to pass the TreeNode in, it will grab the handle of the parent control from the node itself. After applying the formatting to a couple of nodes you’ll get something like this:-

I recently ran into a problem with a Smart Device CAB Project in Visual Studio 2005, which as it turns out is a known issue. You can build a CAB file which will register your .NETCF dlls into the GAC – the File System Editor has a standard folder called “Global Assembly Cache Folder” which you can put your files into. Behind the scenes this deploys the dlls to the windows folder and generates a .GAC text file with a list of paths to your dll(s). The problem is that the generated GAC file is a Unicode text file and doesn’t work on devices prior to Windows Mobile 5.0. I’m assuming the same is true with generic CE 4.2 devices versus CE 5.0. In itself this seems bizarre since CE is fully Unicode based so shouldn’t have any problem reading the file. It just so happens that when you are doing this the old fashioned way with notepad you get an ANSI text file which works just fine on all devices.

The workaround is simple, don’t use the whizzy GAC support in the CAB project, place your dlls into the Windows Folder, and manually create a .GAC text file and place this in the Windows Folder also. The downside to this approach is that you must update your GAC file if you add or remove dlls from your setup project. I’d like to say thanks to fellow MVP Jan Yeh for helping to test the issue and to Manish Vasani from the Visual Studio for Devices team for following up with more details on the issue.