MAUI How to use KeyEvent.Callback in an Android app

Question

The application is written for the data collection terminal (android). It has a physical keyboard. Can you tell me how to intercept keyboard clicks if there is no text field on the form?

Answer 1

The OnKeyListener Class can be used to deal with the input from the physical keyboard:

 public class MyListener : Java.Lang.Object, Android.Views.View.IOnKeyListener
{
    public bool OnKey(Android.Views.View v, [GeneratedEnum] Keycode keyCode, KeyEvent e)
    {
         return true;// true will intercept keyboard clicks
    }
}

And add the listener to the entry when there is no text field on the form:

private void entry_Focused(object sender, FocusEventArgs e)
{
    Entry entry = (Entry)sender;
#if ANDROID
    (entry.Handler.PlatformView as AppCompatEditText).SetOnKeyListener(new MyListener());
#endif
 }

And when the form has text, remove the listener:

Entry entry = (Entry)sender;
#if ANDROID
    (entry.Handler.PlatformView as AppCompatEditText).SetOnKeyListener(null);
#endif

Answer 2

A solution that I have found is this:

1. Define an interface to implement in your pages that you want to "react" to physical keyboard keys (optional - it is used to differentiate pages that you want to react to keys from pages that is not necessary to). A sample:

    #if ANDROID using Android.Views; #endif namespace KeyboardTest { public interface IOnPageKeyDown { #if ANDROID /// <summary> /// Called when a key is pressed. /// </summary> /// <param name="keyCode">The code of pressed key.</param> /// <param name="e">Description of the key event.</param> /// <returns> /// Return true to prevent this event from being propagated further, /// or false to indicate that you have not handled this event and it should continue to be propagated. /// </returns> public bool OnPageKeyDown(Keycode keyCode, KeyEvent e); #endif } }

2. Implement this interface to every page you want to react to keys. Sample:

    #if ANDROID using Android.Views; #endif // Your code here namespace KeyboardTest { public partial class TestPage: ContentPage, IOnPageKeyDown { #if ANDROID public bool OnPageKeyDown(Keycode keyCode, KeyEvent e) { switch (keyCode) { case Keycode.DpadUp: // Your code here return true; case Keycode.DpadDown: // Your code here return true; case Keycode.Enter: // Your code here return true; default: return false; } } #endif } }

3. Override "OnKeyDown" in Platforms/Android/MainActivity.cs. Sample:

    using Android.App; using Android.Content.PM; using Android.OS; using Android.Runtime; using Android.Views; using AndroidX.Core.View; namespace KeyboardTest; // Your code here public class MainActivity: MauiAppCompatActivity { // Your code here public override bool OnKeyDown([GeneratedEnum] Keycode keyCode, KeyEvent e) { Page p = Shell.Current.CurrentPage; if (p is IOnPageKeyDown) { bool handled = (p as IOnPageKeyDown).OnPageKeyDown(keyCode, e); if (handled) return true; else return base.OnKeyDown(keyCode, e); } else return base.OnKeyDown(keyCode, e); } }

I hope that helps.