How do I get keyboard events in the topmost NSPanel?

Question

I have created an app using Xamarin to help watching movies online. It shows the subtitles on top of all other windows. This has been done using the NSPanel , as it was the only way to make it work on MacOS Mojave.

The app works well. Now I want to improve the app by making NSPanel respond to the keyboard events, so I can control the app by using the keyboard for pausing, playing, going backward or going forward.

How do I get keyboard events in the topmost NSPanel ?

I tried to use this code:

NSEvent.AddLocalMonitorForEventsMatchingMask(NSEventMask.KeyDown, KeyboardEventHandler);

private static NSEvent KeyboardEventHandler(NSEvent keyEvent)
{
    // handle key down events here
    return (keyEvent);
}

But it only works when the app is not in the full-screen mode.

The full SubtitlesViewer-MACOS project can be found here .

Here is the part of the code that creates the panel:

public override void ViewWillAppear()
{
    base.ViewWillAppear();
    SetupView();
}

private void SetupView()
{ 
    var screenRes = screenResolution();
    int PANEL_HEIGHT = 200;
    subtitlesPanel = new NSPanel
    (
        new CoreGraphics.CGRect(40, 50, screenRes.Width - 80, PANEL_HEIGHT),
        NSWindowStyle.Titled | NSWindowStyle.Closable | NSWindowStyle.Resizable | NSWindowStyle.Miniaturizable | NSWindowStyle.DocModal,
        NSBackingStore.Buffered, true
    )
    {
        BackgroundColor = NSColor.FromCalibratedRgba(0, 0, 0, 0.0f),
        ReleasedWhenClosed = true,
        HidesOnDeactivate = false,
        FloatingPanel = true,
        StyleMask = NSWindowStyle.NonactivatingPanel,
        Level = NSWindowLevel.MainMenu - 1,
        IsMovable = true,
        CollectionBehavior = NSWindowCollectionBehavior.CanJoinAllSpaces |
        NSWindowCollectionBehavior.FullScreenAuxiliary
    };

    subtitlesPanel.OrderFront(null);

    subtitleTextButton = new NSButton(new CoreGraphics.CGRect(40, 0, screenRes.Width - 120, PANEL_HEIGHT-30))
    {
        Title = "",
        WantsLayer = true
    };

    subtitleTextButton.Layer.BackgroundColor = NSColor.Clear.CGColor;

    subtitleTextField = new NSTextField(new CoreGraphics.CGRect(40, 0, screenRes.Width - 120, PANEL_HEIGHT-30))
    {
        Alignment = NSTextAlignment.Center
    };
    subtitleTextField.Cell.Alignment = NSTextAlignment.Center;

    forwardButton = new NSButton(new CoreGraphics.CGRect(0, 0, 40, 30));
    forwardButton.Title = ">>";
    forwardButton.Activated += (object sender, EventArgs e) => {
        subtitlesProvider.Forward();
    };

    backButton = new NSButton(new CoreGraphics.CGRect(0, 30, 40, 30));
    backButton.Title = "<<";
    backButton.Activated += (object sender, EventArgs e) => {
        subtitlesProvider.Back();
    };

    startStopButton = new NSButton(new CoreGraphics.CGRect(0, 60, 40, 30));
    startStopButton.Title = "Play";
    startStopButton.Activated += (object sender, EventArgs e) => {
        subtitlesProvider.StartStop(subtitlesProvider.Playing);
    };

    subtitlesPanel.ContentView.AddSubview(subtitleTextButton, NSWindowOrderingMode.Below, null);
    subtitlesPanel.ContentView.AddSubview(subtitleTextField, NSWindowOrderingMode.Below, null);

    subtitlesPanel.ContentView.AddSubview(forwardButton, NSWindowOrderingMode.Below, null);
    subtitlesPanel.ContentView.AddSubview(backButton, NSWindowOrderingMode.Below, null);
    subtitlesPanel.ContentView.AddSubview(startStopButton, NSWindowOrderingMode.Below, null);

    SetupSubtitlesProvider();
}

Please kindly advice what else should I try to make it work.

Answer 1

I have found the solution here: keyDown not being called

This is my implementation of NSPanelExt class to handle the keys.

public class NSPanelExt : NSPanel
{
    public KeyPressedHandler KeyPressed;
    public delegate void KeyPressedHandler(KeyCodeEventArgs e);

    public NSPanelExt(CGRect contentRect, NSWindowStyle aStyle, NSBackingStore bufferingType, bool deferCreation) : base(contentRect, aStyle, bufferingType, deferCreation)
    {
    }

    public override bool CanBecomeMainWindow => true;

    public override bool CanBecomeKeyWindow => true;

    public override bool AcceptsFirstResponder()
    {
        return true;
    }


    public override void KeyDown(NSEvent theEvent)
    {
        // this function is never called
        KeyPressed?.Invoke(new KeyCodeEventArgs {  Key = GetKeyCode(theEvent.KeyCode) });

    }

    private KeyCode GetKeyCode(ushort keyCode)
    {
        KeyCode result = KeyCode.Unknown;
        switch (keyCode)
        {
            case 123:
                result = KeyCode.Left;
                break;
            case 49:
                result = KeyCode.Space;
                break;
            case 124:
                result = KeyCode.Right;
                break;
            case 53:
                result = KeyCode.Esc;
                break;
        }

        return result;
    }

I have also updated the ViewController to keep NSPanel always active.

public partial class ViewController : NSViewController
    {
        // ...
        private NSButton startStopButton;
        Timer _timer = new Timer();

        private void SetupView()
        { 
        // ...
    subtitlesPanel.KeyPressed += SubtitlesPanel_KeyPressed;

        // ...   
            IntializeKeepWindowFocusedTimer();
        }

        void SubtitlesPanel_KeyPressed(KeyCodeEventArgs e)
        {
            switch(e.Key)
            {
                case KeyCode.Left:
                    backButton.PerformClick(this);
                    break;
                case KeyCode.Right:
                    forwardButton.PerformClick(this);
                    break;
                case KeyCode.Space:
                    startStopButton.PerformClick(this);
                        break;
                case KeyCode.Esc:
                    _timer.Stop();
                    break;
            }
        }


        private void IntializeKeepWindowFocusedTimer()
        {
            _timer.Interval = 200;  //in milliseconds
            _timer.Elapsed += Timer_Elapsed;;
            _timer.AutoReset = true;
            _timer.Enabled = true;
        }

        void Timer_Elapsed(object sender, ElapsedEventArgs e)
        {
            NSApplication.SharedApplication.BeginInvokeOnMainThread(() =>
            {
                subtitlesPanel.MakeKeyWindow();
                if (SetSubtitleNeeded)
                {
                    subtitlesProvider.SetSubTitle(0);
                    startStopButton.Title = "Stop";
                    SetSubtitleNeeded = false;
                    _timer.Interval = 5000;
                }
            });
        }

        private bool SetSubtitleNeeded = false;

        partial void ClickedButton(NSObject sender)
        {
            _timer.Stop();
            var nsUrl = subtitleFileSelector.GetFile();
            if (nsUrl == null)
                return;

            fileName = nsUrl.Path;
            subtitlesProvider.ReadFromFile(fileName);
            SetSubtitleNeeded = true;
            _timer.Start();
        }