Show Hotkeys at All Times

Is is possible to make the underlining hotkey always visible on my controls without having to press the Alt key in a Windows form with Visual Studio - C#?

I only have a certain time when I need the controls of the form to be always underlined with the "_" under a character. So it would be good to have just the code to do it.

I could have the setting for Windows to always show underlining of shortcuts and hotkeys, but I only need it to happen a certain time.

Assuming you are using WinForms, you should be able to rely on the underlying Win32 mechanism. And that is the WM_UPDATEUISTATE message. The documentation says:

An application sends the WM_UPDATEUISTATE message to change the UI state for the specified window and all its child windows.

So you can send the message to the handle of the top-level window. You need to pass UIS_CLEAR for the low-order word of wParam and UISF_HIDEACCEL for the high-order word of wParam.

Here is some rather crude sample code. Bear in mind that my C# expertise is very limited.

public partial class Form1 : Form
{
    private const uint WM_UPDATEUISTATE = 0x0128;
    private const uint WM_QUERYUISTATE = 0x0129;
    private const uint UIS_CLEAR = 2;
    private const uint UISF_HIDEACCEL = 0x2;

    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_HandleCreated(object sender, PaintEventArgs e)
    {
        ClearHideAccel();
    }

    private void ClearHideAccel()
    {
        UIntPtr wParam = (UIntPtr)((UISF_HIDEACCEL << 16) | UIS_CLEAR);
        NativeMethods.SendMessage(this.Handle, WM_UPDATEUISTATE, wParam, IntPtr.Zero);
    }
}

internal class NativeMethods
{
    [DllImport("User32", SetLastError = true)]
    public static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, UIntPtr wParam, IntPtr lParam);
}