Anyone know how to disable alt+tab or only alt when application is open?

Question

Im making an application and I need the code to do this. Thanks.

Answer 1

You can use a WH_KEYBOARD_LL Hook

A test, on Windows 10 1909 (click on the Button to start the Hook which disables Alt + Tab) =>

public partial class Form1 : Form
{
    public const int WH_MIN = (-1);
    public const int WH_MSGFILTER = (-1);
    public const int WH_JOURNALRECORD = 0;
    public const int WH_JOURNALPLAYBACK = 1;
    public const int WH_KEYBOARD = 2;
    public const int WH_GETMESSAGE = 3;
    public const int WH_CALLWNDPROC = 4;
    public const int WH_CBT = 5;
    public const int WH_SYSMSGFILTER = 6;
    public const int WH_MOUSE = 7;
    public const int WH_HARDWARE = 8;
    public const int WH_DEBUG = 9;
    public const int WH_SHELL = 10;
    public const int WH_FOREGROUNDIDLE = 11;
    public const int WH_CALLWNDPROCRET = 12;
    public const int WH_KEYBOARD_LL = 13;
    public const int WH_MOUSE_LL = 14;
    public const int WH_MAX = 14;
    public const int WH_MINHOOK = WH_MIN;
    public const int WH_MAXHOOK = WH_MAX;

    [StructLayoutAttribute(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    public struct MSLLHOOKSTRUCT
    {
        public System.Drawing.Point pt;
        public int mouseData;
        public int flags;
        public int time;
        public uint dwExtraInfo;
    }

    [StructLayoutAttribute(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    public struct KBDLLHOOKSTRUCT
    {
        public int vkCode;
        public int scanCode;
        public int flags;
        public int time;
        public uint dwExtraInfo;
    }

    public delegate int HookProc(int nCode, IntPtr wParam, IntPtr lParam);

    [DllImport("User32.dll", SetLastError = true, CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
    public static extern int SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hInstance, int threadId);

    [DllImport("User32.dll", SetLastError = true, CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
    public static extern bool UnhookWindowsHookEx(int idHook);

    [DllImport("User32.dll", SetLastError = true, CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
    public static extern int CallNextHookEx(int idHook, int nCode, IntPtr wParam, IntPtr lParam);

    public const int KF_EXTENDED = 0x0100;
    public const int KF_DLGMODE = 0x0800;
    public const int KF_MENUMODE = 0x1000;
    public const int KF_ALTDOWN = 0x2000;
    public const int KF_REPEAT = 0x4000;
    public const int KF_UP = 0x8000;

    public const int LLKHF_EXTENDED = (KF_EXTENDED >> 8); /* 0x00000001 */
    public const int LLKHF_INJECTED = 0x00000010;
    public const int LLKHF_ALTDOWN = (KF_ALTDOWN >> 8); /* 0x00000020 */
    public const int LLKHF_UP = (KF_UP >> 8);      /* 0x00000080 */
    public const int LLKHF_LOWER_IL_INJECTED = 0x00000002;

    public const int LLMHF_INJECTED = 0x00000001;
    public const int LLMHF_LOWER_IL_INJECTED = 0x00000002;

    static int hHook = 0;
    HookProc KeyboardLLProcedure;

    public const int WM_KEYDOWN = 0x0100;
    public const int WM_SYSKEYDOWN = 0x0104;
    public const int VK_SHIFT = 0x10;
    public const int VK_MENU = 0x12;

    [DllImport("User32.dll", SetLastError = true, CharSet = CharSet.Auto)]
    private static extern short GetAsyncKeyState(System.Windows.Forms.Keys vKey);

    public static int KeyboardLLProc(int nCode, IntPtr wParam, IntPtr lParam)
    {
        bool bShiftKeyDown = false;
        bool bAltKeyDown = false;

        if (nCode >= 0)
        {
            bShiftKeyDown = GetAsyncKeyState((Keys)VK_SHIFT) < 0;
            bAltKeyDown = GetAsyncKeyState((Keys)VK_MENU) < 0;
            KBDLLHOOKSTRUCT pKBDLLHOOKSTRUCT = new KBDLLHOOKSTRUCT();
            pKBDLLHOOKSTRUCT = (KBDLLHOOKSTRUCT)Marshal.PtrToStructure(lParam, pKBDLLHOOKSTRUCT.GetType());

            //if (pKBDLLHOOKSTRUCT.vkCode == (short)Keys.LWin)
            if (pKBDLLHOOKSTRUCT.vkCode == (short)Keys.Tab && bAltKeyDown)
            {
                Console.Beep(8000, 10);
                return 1;
            }
        }
        return nCode < 0 ? CallNextHookEx(hHook, nCode, wParam, lParam) : 0;
    }

    private System.Windows.Forms.Button button1;
    public Form1()
    {
        //InitializeComponent();
        this.button1 = new System.Windows.Forms.Button();
        this.button1.Location = new System.Drawing.Point(104, 114);
        this.button1.Name = "button1";
        this.button1.Size = new System.Drawing.Size(75, 23);
        this.button1.TabIndex = 0;
        this.button1.Text = "button1";
        this.button1.UseVisualStyleBackColor = true;
        this.button1.Click += new System.EventHandler(this.button1_Click);
        this.Controls.Add(this.button1);
        this.FormClosing += new System.Windows.Forms.FormClosingEventHandler(this.Form1_FormClosing);
        CenterToScreen();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        if (hHook == 0)
        {
            KeyboardLLProcedure = new HookProc(KeyboardLLProc);
            hHook = SetWindowsHookEx(WH_KEYBOARD_LL, KeyboardLLProcedure, (IntPtr)0, 0);
        }
    }

    private void Form1_FormClosing(object sender, FormClosingEventArgs e)
    {
        if (hHook != 0)
            UnhookWindowsHookEx(hHook);
    }      
}