How to hide desktop icons programmatically?

Even though this is quite old when I tried Ondrej Balas's answer, one problem I found with this solution is that it does not work if the ToggleDesktop command is used to show the desktop ( also if wallpaper rotation is enabled ).

In both of these cases the SHELLDLL_DefView window, which is the recipient of the toggleDesktopCommand in the ToggleDesktopIcons function, is not a child of the "Program manager" window but of a 'WorkerW" window. (see WinApi - How to obtain SHELLDLL_DefView and Windows Desktop ListView Handle.

Based on those and building upon Ondrej Balas's earlier answer change the ToggleDesktopIcons function to be :

static void ToggleDesktopIcons()
{
    var toggleDesktopCommand = new IntPtr(0x7402);
    SendMessage(GetDesktopSHELLDLL_DefView(), WM_COMMAND, toggleDesktopCommand, IntPtr.Zero);
}

And add a GetDesktopSHELLDLL_DefView function:

    [DllImport("user32.dll", SetLastError = true)]
    public static extern IntPtr FindWindowEx(IntPtr parentHandle, IntPtr childAfter, string className, string windowTitle);
    [DllImport("user32.dll", SetLastError = false)]
    static extern IntPtr GetDesktopWindow();

    static IntPtr GetDesktopSHELLDLL_DefView()
    {
        var hShellViewWin = IntPtr.Zero;
        var hWorkerW = IntPtr.Zero;

        var hProgman = FindWindow("Progman", "Program Manager");
        var hDesktopWnd = GetDesktopWindow();

        // If the main Program Manager window is found
        if (hProgman != IntPtr.Zero)
        {
            // Get and load the main List view window containing the icons.
            hShellViewWin = FindWindowEx(hProgman, IntPtr.Zero, "SHELLDLL_DefView", null);
            if (hShellViewWin == IntPtr.Zero)
            {
                // When this fails (picture rotation is turned ON, toggledesktop shell cmd used ), then look for the WorkerW windows list to get the
                // correct desktop list handle.
                // As there can be multiple WorkerW windows, iterate through all to get the correct one
                do
                {
                    hWorkerW = FindWindowEx(hDesktopWnd, hWorkerW, "WorkerW", null);
                    hShellViewWin = FindWindowEx(hWorkerW, IntPtr.Zero, "SHELLDLL_DefView", null);
                } while (hShellViewWin == IntPtr.Zero && hWorkerW != IntPtr.Zero);
            }
        }
        return hShellViewWin;
    }

Now regardless of the desktop toggle or wallpaper rotation the ToggleDesktopIcons should always work.

For reference this is my toggle desktop function which caused the issue with the original ToggleDesktopIcons function

static public void ToggleDesktop(object sender, EventArgs e)
        {
            var shellObject = new Shell32.Shell();
            shellObject.ToggleDesktop();
        }

In response to James M, this function returns the current state:

bool IconsVisible()
{
    var hWnd = GetDesktopListView();
    var info = new User32.WINDOWINFO(null);
    User32.GetWindowInfo(hWnd, ref info);
    return (info.dwStyle & User32.WindowStyle.WS_VISIBLE) == User32.WindowStyle.WS_VISIBLE;
}

A different approach is to create a separate desktop and show it instead. It will not have icons.

Application running itself on a separate desktop

You can do this using the Windows API. Here is sample code in C# that will toggle desktop icons.

    [DllImport("user32.dll", SetLastError = true)] static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
    [DllImport("user32.dll", SetLastError = true)] static extern IntPtr GetWindow(IntPtr hWnd, GetWindow_Cmd uCmd);
    enum GetWindow_Cmd : uint
    {
        GW_HWNDFIRST = 0,
        GW_HWNDLAST = 1,
        GW_HWNDNEXT = 2,
        GW_HWNDPREV = 3,
        GW_OWNER = 4,
        GW_CHILD = 5,
        GW_ENABLEDPOPUP = 6
    }
    [DllImport("user32.dll", CharSet = CharSet.Auto)] static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, IntPtr lParam);

    private const int WM_COMMAND = 0x111;

    static void ToggleDesktopIcons()
    {
        var toggleDesktopCommand = new IntPtr(0x7402);
        IntPtr hWnd = GetWindow(FindWindow("Progman", "Program Manager"), GetWindow_Cmd.GW_CHILD);
        SendMessage(hWnd, WM_COMMAND, toggleDesktopCommand, IntPtr.Zero);
    }

This sends a message to the SHELLDLL_DefView child window of Progman, which tells it to toggle visibility (by adding or removing the WS_VISIBLE style) of it's only child, "FolderView". "FolderView" is the actual window that contains the icons.

To test to see if icons are visible or not, you can query for the WS_VISIBLE style by using the GetWindowInfo function, shown below:

    [return: MarshalAs(UnmanagedType.Bool)]
    [DllImport("user32.dll", SetLastError = true)]
    private static extern bool GetWindowInfo(IntPtr hwnd, ref WINDOWINFO pwi);

    [StructLayout(LayoutKind.Sequential)]
    public struct RECT
    {
        private int _Left;
        private int _Top;
        private int _Right;
        private int _Bottom;
    }

    [StructLayout(LayoutKind.Sequential)]
    struct WINDOWINFO
    {
        public uint cbSize;
        public RECT rcWindow;
        public RECT rcClient;
        public uint dwStyle;
        public uint dwExStyle;
        public uint dwWindowStatus;
        public uint cxWindowBorders;
        public uint cyWindowBorders;
        public ushort atomWindowType;
        public ushort wCreatorVersion;

        public WINDOWINFO(Boolean? filler)
            : this()   // Allows automatic initialization of "cbSize" with "new WINDOWINFO(null/true/false)".
        {
            cbSize = (UInt32)(Marshal.SizeOf(typeof(WINDOWINFO)));
        }

    }

Here is a function that calls the above code and returns true if the window is visible, false if not.

    static bool IsVisible()
    {
        IntPtr hWnd = GetWindow(GetWindow(FindWindow("Progman", "Program Manager"), GetWindow_Cmd.GW_CHILD), GetWindow_Cmd.GW_CHILD);
        WINDOWINFO info = new WINDOWINFO();
        info.cbSize = (uint)Marshal.SizeOf(info);
        GetWindowInfo(hWnd, ref info);
        return (info.dwStyle & 0x10000000) == 0x10000000;
    }

The windows API code along with more information about the window styles can be found here: http://www.pinvoke.net/default.aspx/user32/GetWindowInfo.html