Android UI How to - Execute Javascript in WebView

The following code shows how to Execute Javascript in WebView.

Example

Main layout xml file

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="hello"
    />
</LinearLayout>

Main Activity Java code

package com.java2s.myapplication3.app;
//from   w  w  w  .  j a v  a  2  s .  c  o  m
import android.annotation.TargetApi;
import android.app.Activity;
import android.content.SharedPreferences;
import android.os.Build;
import android.os.Bundle;
import android.text.TextUtils;
import android.webkit.JavascriptInterface;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;

public class MainActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        WebView webview = new WebView(this);
        webview.getSettings().setJavaScriptEnabled(true);
        webview.setWebViewClient(mClient);
        webview.addJavascriptInterface(new MyJavaScriptInterface(), "BRIDGE");

        setContentView(webview);

        webview.loadUrl("file:///android_asset/form.html");
    }

    private static final String JS_SETELEMENT = "javascript:document.getElementById('%s').value='%s'";
    private static final String JS_GETELEMENT = "javascript:window.BRIDGE.storeElement('%s',document.getElementById('%s').value)";
    private static final String ELEMENTID = "emailAddress";

    private WebViewClient mClient = new WebViewClient() {
        @Override
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            executeJavascript(view,String.format(JS_GETELEMENT, ELEMENTID, ELEMENTID) );
            return false;
        }

        @Override
        public void onPageFinished(WebView view, String url) {
            SharedPreferences prefs = getPreferences(Activity.MODE_PRIVATE);
            executeJavascript(view,String.format(JS_SETELEMENT, ELEMENTID, prefs.getString(ELEMENTID, "")) );
        }
    };

    private void executeJavascript(WebView view, String script) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
            view.evaluateJavascript(script, null);
        } else {
            view.loadUrl(script);
        }
    }
    class MyJavaScriptInterface {
        @JavascriptInterface
        public void storeElement(String id, String element) {
            SharedPreferences.Editor edit = getPreferences(Activity.MODE_PRIVATE).edit();
            edit.putString(id, element);
            edit.commit();
            if(!TextUtils.isEmpty(element)) {
                Toast.makeText(MainActivity.this, element, Toast.LENGTH_SHORT).show();
            }
        }
    }

}

\assets\form.html

<!DOCTYPE HTML>
<html>
<form name="input" action="form.html" method="get">
Enter Email: <input type="text" id="emailAddress" />
<input type="submit" value="Submit" />
</form>
</html>