全局捕获键盘（包含未激活状态）

[STAThread]
static void Main()
{
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);
    _hookID = SetHook(_proc);
    Form1 form1 = new Form1();
    Application.Run(form1);
    UnhookWindowsHookEx(_hookID);
}

private const int WH_KEYBOARD_LL = 13;
private const int WM_KEYDOWN = 0x0100;
private const int VK_F1 = 0x70;
private static LowLevelKeyboardProc _proc = HookCallback;
private static IntPtr _hookID = IntPtr.Zero;

private static IntPtr SetHook(LowLevelKeyboardProc proc)
{
    using (Process curProcess = Process.GetCurrentProcess())
    using (ProcessModule curModule = curProcess.MainModule)
    {
        return SetWindowsHookEx(WH_KEYBOARD_LL, proc, GetModuleHandle(curModule.ModuleName), 0);
    }
}

private delegate IntPtr LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);

private static IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
{
    if (nCode >= 0)
    {
        Keys number = (Keys)Marshal.ReadInt32(lParam);

        //if (number == Keys.PrintScreen)
        //{
        //    if ((wParam == (IntPtr)260 && Keys.Alt == Control.ModifierKeys && number == Keys.PrintScreen))
        //    {
        //        MessageBox.Show("You pressed alt+ print screen");
        //    }
        //}

        Form1 form = (Form1)Application.OpenForms["Form1"];
        form.label.Text = number.ToString();
    }
    return CallNextHookEx(IntPtr.Zero, nCode, wParam, lParam);
}

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr SetWindowsHookEx(int idHook, LowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId);
[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool UnhookWindowsHookEx(IntPtr hhk);

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);

[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr GetModuleHandle(string lpModuleName);