Sometimes message from exception that occurred inside .Net CF classes doesn’t look handly at all:

An error message cannot be displayed because an optional resource assembly containing it cannot be found.

The thing is that error messages are actually in the resource assembly which is not installed on the device. So to fix the problem you just need to install this assembly:

1. Navigate to CompactFramework folder in the SDK which is “%Program Files%\Microsoft.NET\SDK\CompactFramework”.
2. Navigate to Diagnostics folder under desired .Net CF version (“v3.5\WindowsCE\Diagnostics” for 3.5 or “v2.0\WindowsCE\Diagnostics” for 2.0).
3. Copy resource CAB file to device according to the language you want and install it.

Below is a snapshot that shows how to change screen orientation from normal to 90 degree rotated or from 90 degree back to normal depending on current screen state:

if (SystemSettings.ScreenOrientation == ScreenOrientation.Angle0) {
	SystemSettings.ScreenOrientation = ScreenOrientation.Angle90;
}
else {
	SystemSettings.ScreenOrientation = ScreenOrientation.Angle0;
}

To make this code compile don’t forget to import Microsoft.WindowsCE.Forms namespace.

New home screen available in Windows Mobile 6.5 should be refreshed differently for Professional and Standard editions of OS. It can be done using the same API methods as for earlier versions of Windows Mobile.

For Professional edition it can be done like this:

[DllImport("coredll.dll")]
private static extern IntPtr PostMessage(int hWnd, int msg, uint wParam, uint lParam);

private const int HWND_BROADCAST = 0xFFFF;
private const int WM_WININICHANGE = 0x001A;

public static void Refresh() {
	PostMessage(HWND_BROADCAST, WM_WININICHANGE, 0xF2, 0);
}

For Standard edition the trick is to provide correct GUID to API. This GUID can be found in SlidingPanel.home.xml file located in “\Application Data\Home” folder. Here is the code:

[DllImport("aygshell.dll")]
public extern static uint SHOnPluginDataChange(ref Guid clsid);

public static void Refresh() {
	Guid guid = new Guid("{E9267CAB-02EE-4f37-8216-6BF6A8FF5A71}");
	SHOnPluginDataChange(ref guid);
}

Here is a code for loading embedded image named MyImage.png stored directly in project directory:

Assembly assembly = Assembly.GetExecutingAssembly();
string iconFileName = string.Format("{0}.MyImage.png", assembly.GetName().Name);
using (Stream io = assembly.GetManifestResourceStream(iconFileName)) {
	return new Bitmap(io);
}

Name of resource to load contains three elements divided by dots:

• Assembly name;
• Path where resource is stored inside of a project (must be omitted if resource is in project directory);
• File name of resource.

Path to resource should be created using names of folders. For example, if resource is in “Resources/Images” folder than path will be “Resources.Images”.

Making read-only file writable with full .Net Framework is a piece of cake: there is FileInfo.IsReadOnly. Just set it to false and it’s done.

With Compact Framework we need to use FileInfo.Attributes and a solid knowledge of bitwise operations:

FileInfo info = new FileInfo(pathToReadonlyFile);
info.Attributes &= ~FileAttributes.ReadOnly;

As I wrote in Linkpool: Windows Mobile 6.1 and 6.2 Build Numbers they have the same version (which by the way is 5.2). So checking if application is running under WM 6.5 must be based on build number. Like this:

Version osVersion = Environment.OSVersion.Version;
if (osVersion.Major == 5 && osVersion.Minor == 2 && osVersion.Build >= 21139) {
    // It's Windows Mobile 6.5
}

List of .Net Compact Framework versions installed on device are available in registry under:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETCompactFramework

This key contains a set of DWORD values with names in format X.Y.BBBB.mm that correspond to build numbers of .Net CF (build numbers can be found in Wikipedia). Each of these values can have data of 0 (installed in RAM) or 1 (installed in ROM). So to verify if specific version of .Net CF is installed we need to check if value with corresponding name exists.

Here is a method that checks for .Net CF 2  (I wrote it today to verify available .Net CF versions in setup.dll of cab installer):

BOOL IsNetCF2Installed() {
	BOOL bNetCF2Found = FALSE;

	HKEY hKey = NULL;
	if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, _T("Software\\Microsoft\\.NETCompactFramework"), 0, KEY_READ | KEY_QUERY_VALUE, &hKey) == ERROR_SUCCESS) {
		DWORD dwIndex = 0;
		TCHAR szName[255];
		DWORD cName = 255;
		while ((!bNetCF2Found) && (::RegEnumValue(hKey, dwIndex, szName, &cName, NULL, NULL, NULL, NULL) == ERROR_SUCCESS)) {
			if (szName[0] == '2') {
				bNetCF2Found = TRUE;
			}
			dwIndex++;
		}

		RegCloseKey(hKey);
	}

	return bNetCF2Found;
}