JavascriptInterface in Xamarin.Android is obsolete and cant invoke C# from Javascript

Question

few months ago I had a custom Xamarin.Android renderer for a webview based on the sample code in https://learn.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/custom-renderer/hybridwebview

Javascript code was perfectly invoking my C# code however recently after the latest updates, the WebView control is no longer able to invoke the C# action, (to be more precise, if I am targeting Android 9.0 (API level 28) or higher) using API level 27 still works fine

after more investigation, I figured out that the compiler gives a warning on [JavascriptInterface] is being obsolete! https://learn.microsoft.com/en-us/dotnet/api/android.webkit.javascriptinterface?view=xamarin-android-sdk-9 and they advised to use the (IJavascriptInterface) instead

here is the code to be reviewed

[JavascriptInterface]
[Export ("invokeAction")]
public void InvokeAction (string data)
{
    HybridWebViewRenderer hybridRenderer;
    if (hybridWebViewRenderer != null && hybridWebViewRenderer.TryGetTarget (out hybridRenderer))
    {
        hybridRenderer.Element.InvokeAction (data);
    }
}

Does anyone know how to implement this properly to fix that and get Javascript to invoke my C# code again.

Answer 1

it still works in my Xamarin.Android project with [JavascriptInterface]

this is part of my sample :

var webview = FindViewById<WebView>(Resource.Id.webView1);
WebSettings settings = webview.Settings;
settings.JavaScriptEnabled = true;
// load the javascript interface method to call the foreground method
webView.AddJavascriptInterface(new MyJSInterface(this), "CSharp");
webview.SetWebViewClient(new WebViewClient());

MyJSInterface class :

class MyJSInterface : Java.Lang.Object
{
  Context context;

 public MyJSInterface (Context context)
  {
    this.context = context;
  }

 [JavascriptInterface]
 [Export]
 public void ShowToast (string msg)
  {
    Toast.MakeText(context, msg, ToastLength.Short).Show();
  }
}

and in html :

<button type="button" onClick="CSharp.ShowToast ('Call C#')">Call C#</button>

you could refer to https://stackoverflow.com/a/54069075/10768653