Is it possible to hook into Hardware keyboard events at an Application level?

Question

I am developing a Xamarin.Forms application for iOS, Android and UWP.

I would like to hook into hardware keyboard

Answer 1

I needed to allow numeric input + an enter at the end in my XamForms app. Here's how I solved it in Xamarin Forms 3.0.0.482510 / Xamarin.iOS 11.10 (it's a little different than Kevin's answer above because I wanted to handle it in the XamForms shared xaml project, not in the iOS project):

In your iOS project (with a Xamarin Forms shared project in the solution named 'MobileProject' for example), create a new class:

using Foundation;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;

[assembly: ExportRenderer(typeof(MobileProject.MainPage), typeof (com.YourCompany.iOS.KeyboardHookRenderer))]
namespace com.YourCompany.iOS
{
public class KeyboardHookRenderer : PageRenderer
{
    private string _RecvValue = string.Empty;

    public override bool CanBecomeFirstResponder
    {
        get { return true; }
    }

    protected override void OnElementChanged(VisualElementChangedEventArgs e)
    {
        base.OnElementChanged(e);
        string key = string.Empty;
        var selector = new ObjCRuntime.Selector("KeyRecv:");
        UIKeyCommand accelerator1 = UIKeyCommand.Create((NSString)"1", 0, selector);
        AddKeyCommand(accelerator1);
        UIKeyCommand accelerator2 = UIKeyCommand.Create((NSString)"2", 0, selector);
        AddKeyCommand(accelerator2);
        UIKeyCommand accelerator3 = UIKeyCommand.Create((NSString)"3", 0, selector);
        AddKeyCommand(accelerator3);

        ... etc as many as you need or use a loop based on key id...
    }

    [Export("KeyRecv:")]
    public void KeyRecv(UIKeyCommand cmd)
    {
        if (cmd == null)
            return;
        var inputValue = cmd.Input;
        if (inputValue == "\n" || inputValue == "\r")
        {
            ((MobileProject.MainPage) Element)?.HandleHardwareKeyboard(_RecvValue);
            _RecvValue = string.Empty;
        }
        else
        {
            _RecvValue += inputValue;
        }
    }
}
}

Then, in your shared app in MainPage.xaml.cs, you just need:

/// 

/// Handle hardware keys (from KeyboardHookRender.cs in iOS project)
/// 
/// Keys sent, including trailing Cr or Lf
public void HandleHardwareKeyboard(string keys)
{
    SomeTextbox.Text = keys;
    // Whatever else you need to do to handle it
}