Android WebView showToast onButtonClick

You can solve your problem by implementing a simple JavaScript interface. Below is a simple sample.

assets/button_demo.xml

<html>
<head></head>
<body style="margin:0; padding:0;">
<style type="text/css">
    #demo {
    height: 100%;
    width: 100%;
    margin-left: auto;
    margin-right: auto;
    overflow: auto;
    }
    #demo a {
    font-family: sans-serif;
    font-size: 8pt;
    width: 95%;
    height: 35px;
    display: block;
    margin-left: auto;
    margin-right: auto;
    text-align: center;
    padding: 5px;
    margin: 1px;
    border: 1px solid blue;
    text-decoration: none;
    color: blue;
    word-wrap: break-word;

    }
</style>
<script type="text/javascript">

    function showToast(str){
        Android.showToast(str);
    }

</script>
<div id="demo">
    <a href="javascript: showToast('test')">button</a>
</div>
</body>
</html>

activity_main.xml

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <WebView
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:id="@+id/webView"
        android:layout_centerVertical="true"/>

</RelativeLayout>

MainActivity.java

import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.text.TextUtils;
import android.util.Log;
import android.webkit.JavascriptInterface;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;

import java.lang.ref.WeakReference;


public class MainActivity extends ActionBarActivity {

    private static final String TAG = MainActivity.class.getSimpleName();
    private WebView webView;

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

        webView = (WebView) findViewById(R.id.webView);
        WebSettings webSettings = webView.getSettings();
        webSettings.setJavaScriptEnabled(true);
        webView.setWebViewClient(new MyWebClient());
        webView.addJavascriptInterface(new WebInterface(MainActivity.this), "Android");
        webView.loadUrl("file:///android_asset/button_demo.html");
    }

    private class MyWebClient extends WebViewClient {


        /**
         * It is a good idea to let proper web browsers handle URLs you don't know otherwise
         * you could be putting your users to danger by injecting JavaScript interface
         */


        @Override
        public boolean shouldOverrideUrlLoading(WebView view, String url) {

            //return super.shouldOverrideUrlLoading(view, url);
            Uri uri;

            try {
                uri = Uri.parse(url);
            } catch (NullPointerException e) {
                // let Android deal with this
                return true;
            }

            String host = uri.getHost(); //Host is null when user clicked on email, phone number, ...

            if (host != null && host.equals("stackoverflow.com")) {
                // This is my web site, so do not override; let my WebView load the page
                return false;
            }
            else {
                // Otherwise, the link is not for a page on my site, so launch another Activity that handles URLs or anything else (email, phone number, ...)
                Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
                startActivity(intent);
                return true;
            }
        }

        @Override
        public void onPageFinished(WebView view, String url) {
            Log.d(TAG, "Page finished loading");
            super.onPageFinished(view, url);
        }

        @Override
        public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
            // No connection or HTTP error e.g. 404
            Log.d(TAG, "Received webview error: " + errorCode + " - " + description + " ; " + failingUrl);
        }
    }

    private final class WebInterface {
        /**
         * Caution: If you've set your targetSdkVersion to 17 or higher, you must
         * add the @JavascriptInterface annotation to any method that you want
         * available to your JavaScript (the method must also be public). If you do
         * not provide the annotation, the method is not accessible by your web page
         * when running on Android 4.2 or higher.
         */

        private WeakReference<Activity> mContextRef;
        private Toast toast;

        public WebInterface(Activity context) {
            this.mContextRef = new WeakReference<Activity>(context);
        }

        @JavascriptInterface
        public void showToast(final String toastMsg) {

            if (TextUtils.isEmpty(toastMsg) || mContextRef.get() == null) {
                return;
            }

            // JavaScript doesn't run on the UI thread, make sure you do anything UI related like this
            // You don't need this for the Toast, but otherwise it's a good idea
            mContextRef.get().runOnUiThread(new Runnable() {
                @Override
                public void run() {

                    if (toast != null) {
                        toast.cancel();
                    }

                    toast = Toast.makeText(mContextRef.get(), toastMsg, Toast.LENGTH_SHORT);
                    toast.show();
                }
            });

        }


    }
}

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