Javascript Interface for Android and Javascript communication

The following is an example of two way communication between Android code and Javascript in a WebView.

Enable internet permission and register the WebViewActivity class

The layout for the WebViewActivity class

The WebAppInterface.java for communcating between Android and javascript.

import android.content.Context;
import android.os.Build;
import android.webkit.JavascriptInterface;
import android.widget.Toast;

public class WebAppInterface {
    Context mContext;

    // Instantiate the interface and set the context
    WebAppInterface(Context c) {
        mContext = c;
    }

    // Show a toast from the web page
    @JavascriptInterface
    public void showToast(String toast) {
        Toast.makeText(mContext, toast, Toast.LENGTH_SHORT).show();
    }

    @JavascriptInterface
    public int getAndroidVersion() {
        return android.os.Build.VERSION.SDK_INT;
    }

    @JavascriptInterface
    public void showAndroidVersion(String versionName) {
        Toast.makeText(mContext, versionName, Toast.LENGTH_SHORT).show();
    }

}

The WebView class WebViewActivity.java

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.webkit.JsResult;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class WebViewActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_webview);

        WebView webView = (WebView) findViewById(R.id.webview);
        webView.loadUrl("file:///android_asset/index.html");

        webView.addJavascriptInterface(new WebAppInterface(this), "AndroidInterface"); // To call methods in Android from using js in the html, AndroidInterface.showToast, AndroidInterface.getAndroidVersion etc
        WebSettings webSettings = webView.getSettings();
        webSettings.setJavaScriptEnabled(true);
        webView.setWebViewClient(new MyWebViewClient());
        webView.setWebChromeClient(new MyWebChromeClient());
    }


    private class MyWebViewClient extends WebViewClient {
        @Override
        public void onPageFinished (WebView view, String url) {
            //Calling a javascript function in html page
            view.loadUrl("javascript:alert(showVersion('called by Android'))");
        }
    }

    private class MyWebChromeClient extends WebChromeClient {
        @Override
        public boolean onJsAlert(WebView view, String url, String message, JsResult result) {
            Log.d("LogTag", message);
            result.confirm();
            return true;
        }
    }
}

The html file in assets folder, index.html

Complete example in Github