How to run a JavaScript function and get return in Android?

Question

I\'m working on a project in Xamarin C# and I\'m having trouble running some Java Script. Is there currently a way to call a specific JS function and receive its return value?

Answer 1

you could do like this

Js calls methods in C#

Configure the OnCreate method in the Activity :

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());

Create a C# 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 then it's called in JS ：

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

You can refer to this document：https://github.com/xamarin/recipes/tree/master/Recipes/android/controls/webview/call_csharp_from_javascript

C# calls a method in JS and gets the callback value

webView.EvaluateJavascript("javascript: callJS();", new EvaluateBack());

class EvaluateBack : Java.Lang.Object,IValueCallback
    {

        public void OnReceiveValue(Object value)
        {

            Toast.MakeText(Android.App.Application.Context, value.ToString(), ToastLength.Short).Show();// you will get the value "100"
        }
    }

in JS :

<script>
      function callJS(){
        return 100;
      }
</script>