How to make WPF MenuBar visibile when ALT-key is pressed?

Question

Today I got some new restrictions on my WPF user interface that should eliminate the permanent visibility of the MenuBar.

I thought of imitating the user interface of Windows Live Messenger. That application displays the MenuBar only if the ALT-key is pressed. And hides it again when the focus on the MenuBar is lost.

Currently I don't have a clue how to build such a thing in WPF... is something like this possible?

Thanks in advance.

score 4 · Accepted Answer · answered Jul 13 '11 at 13:17

4

You can write a key down event on main window..

KeyDown="Window_KeyDown"

and in the code behind file..

 private void Window_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.Key == Key.LeftAlt || e.Key == Key.RightAlt)
            {
                myMenu.Visibility = Visibility.Visible;
            }
        }

if you want to achive this with MVVM or using bindings... you can use input key bindings

 <Window.InputBindings>
        <KeyBinding Key="LeftAlt" Command="{Binding ShowMenuCommand}"/>
        <KeyBinding Key="RightAlt" Command="{Binding ShowMenuCommand}"/>
    </Window.InputBindings>

answered Jul 13 '11 at 13:17

Bathineni

3,436
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Guess this is just a code behind job. MVVM does fit in, but shouldn't be used for this I guess. Tried it, it works. However, in all answers I miss the part where the menubar will be collapsed again. – Herman Cordes Jul 14 '11 at 09:47
I've used the above solution. Added the Key.System too. All LostFocus events didn't seem to work properly however. Only the MenuBar.IsMouseCaptureWithinChanged event does the job properly. – Herman Cordes Jul 15 '11 at 09:10

rittergig · Answer 2 · 2020-05-23T19:59:25.767

Try the following solution - a better and more compact solution in WPF. This also works if your control has not the focus or if you programatically enter the menu mode via InputManager.Current.PushMenuMode(menuSite); (see the end of the post).

Add the following code to your window or user control which contains your menu myMenu - for example at the end of your constructor:

this.myMenu.Height = 0; // Initially hide the menu
InputManager.Current.EnterMenuMode += this.InputManager_MenuModeToggled;
InputManager.Current.LeaveMenuMode += this.InputManager_MenuModeToggled;

Then implement the event handler:

private void InputManager_MenuModeToggled(object sender, EventArgs e)
{
    if (!InputManager.Current.IsInMenuMode)
        this.myMenu.Height = 0; // 0 to hide the menu
    else
        this.myMenu.Height = double.NaN; // NaN to reset the height (auto height)
}

Consider the following notes:

Set Height=0 instead of Visiblity to Collapsed/Hidden, because if the menu is invisible then the menu mode may not will be entered when Alt key will be pressed.
The menu must contains at least ony item, otherwise the menu mode may not will be entered when Alt key will be pressed.
In my opinion this solution also applies to MVVM applications, because its UI logic and not View Model logic.

Tested with target framework .NET Framework 4.5 within a WPF app on a Windows 10 machine.

Added:

If you want to enter the menu mode programmatically you can call the menu mode via: InputManager.Current.PushMenuMode(menuSite); However I had the issue that if I call the method PushMenuMode that after then the menu mode never will be leaved. So I fixed this with following solution:

PresentationSource source = PresentationSource.FromVisual(this);
InputManager.Current.PushMenuMode(menuSite: source);
this.Menu.Focus();

RoutedEventHandler lostFocus = null;
lostFocus = (s, args) =>
{
    InputManager.Current.PopMenuMode(menuSite: source);
    this.Menu.LostFocus -= lostFocus;
};
this.Menu.LostFocus += lostFocus;

score 1 · Answer 3 · answered Jul 13 '11 at 13:49

I think that the correct implementation is with KeyUp. This is the behaviour of IE8, Vista, Windows7 and other recent MS products:

private void MainWindow_KeyUp(Object sender, KeyEventArgs e)
    {
        if (e.Key == Key.System)
        {
            if (mainMenu.Visibility == Visibility.Collapsed)
                mainMenu.Visibility = Visibility.Visible;
            else
                mainMenu.Visibility = Visibility.Collapsed;
        }
    }

score 0 · Answer 4 · answered Jul 13 '11 at 13:11

This is what I understood:

private void form_KeyDown(object sender, 
    System.Windows.Forms.KeyEventArgs e)
{
    if(e.KeyCode == Keys.Alt && /*menu is not displayed*/) 
    {
        // display menu
    } 
}

private void form_KeyUp(object sender,
    System.Windows.Forms.MouseEventArgs e)
{
    if (/*check if mouse is NOT over menu using e.X and e.Y*/)
    {
        // hide menu
    }
}

If you need something different play a little with keyboard and mouse events.

score 0 · Answer 5 · answered Jul 13 '11 at 13:14

You can use the KeyDown (or Preview version if you prefer) and then check for the System key like this:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        this.KeyDown += new KeyEventHandler(MainWindow_KeyDown);
    }

    void MainWindow_KeyDown(object sender, KeyEventArgs e)
    {
        if (e.Key == Key.System && (Keyboard.Modifiers & ModifierKeys.Alt) == ModifierKeys.Alt)
        {
            // ALT key pressed!
        }
    }
}

How to make WPF MenuBar visibile when ALT-key is pressed?

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