Using JavaScript in Android Webview

using javascript in android webview

You have to first register the JavaScriptInterface on your webview.
JavaScriptInterFace can be a inner class as shown below. This class will have a function that you can call from html page( via javaScript ) and inside this function you can write code to change activity.

Here is the working solution for you:

public class JavascriptInterfaceActivity extends Activity {
    /** Called when the activity is first created. */

    WebView wv;

    JavaScriptInterface JSInterface;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        wv = (WebView)findViewById(R.id.webView1);

        wv.getSettings().setJavaScriptEnabled(true);
        // register class containing methods to be exposed to JavaScript

        JSInterface = new JavaScriptInterface(this);
        wv.addJavascriptInterface(JSInterface, "JSInterface"); 

        wv.loadUrl("file:///android_asset/myPage.html");

    }

    public class JavaScriptInterface {
        Context mContext;

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

        @android.webkit.JavascriptInterface
        public void changeActivity()
        {
            Intent i = new Intent(JavascriptInterfaceActivity.this, nextActivity.class);
            startActivity(i);
            finish();
        }
    }
}

Here is the html page

<html>
<head>
<script type="text/javascript">
function displaymessage()
{
JSInterface.changeActivity();
}
</script>
</head>

<body>
<form>
<input type="button" value="Click me!" onclick="displaymessage()" />
</form>
</body>
</html>

Hope this helps...

Run JavaScript in Android webview

Well I replaced:

if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.KITKAT) {
    webview.evaluateJavascript(javascript, null);
} else {
    webview.loadUrl("javascript:(function(){" + javascript + "})()");
}

with

webview.setWebViewClient(new WebViewClient() {
    public void onPageFinished(WebView webview, String url) {
        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.KITKAT) {
            webview.evaluateJavascript(javascript, null);
        } else {
            webview.loadUrl("javascript:(function(){" + javascript + "})()");
        }
    }
});

and it just WORKS!

How to load a Javascript in WebView

You can do it like this :

private static class WC extends WebViewClient {
    Handler handler1 = null;
    WebView webView = null;
    byte[] b = null;

    public WC(Handler handler, WebView webView) {
        this.handler1 = handler;
        this.webView = webView;
    }

    @Override
    public void onPageFinished(final WebView view, String url) {
        super.onPageFinished(view, url);
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    injectScriptFromNetWork("http://192.168.216.254:4000/test.js");
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();

    }

    private void injectScriptFromNetWork(String urlStr) throws IOException {

        URL url = new URL(urlStr);
        HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
        int code = urlConnection.getResponseCode();
        if (code == 200) {
            InputStream inputStream = urlConnection.getInputStream();
            b = new byte[inputStream.available()];
            inputStream.read(b);
        }

        handler1.post(new Runnable() {
            @Override
            public void run() {
                String jsSource = Base64.encodeToString(b, Base64.NO_WRAP);
                webView.loadUrl("javascript:(function() {" +
                        "var parent = document.getElementsByTagName('head').item(0);" +
                        "var script = document.createElement('script');" +
                        "script.type = 'text/javascript';" +
                        "script.innerHTML = window.atob('" + jsSource + "');" +
                        "parent.appendChild(script)" +
                        "})()");
            }
        });
    }
}

MainActivity.java code like this:

handler = new Handler(getMainLooper());
webView.setWebViewClient(new WC(handler, webView));
webView.loadUrl("file:///android_asset/index.html");

Forgave me, this is my first time answering questions on stackoverflow.

JavaScript in WebView - Android Studio

allow javascript in your webview:

myWebView.getSettings().setJavaScriptEnabled(true);

Run javascript code in Webview

From kitkat onwards use evaluateJavascript method instead loadUrl to call the javascript functions like below

    if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.KITKAT) {
        webView.evaluateJavascript("var FunctionOne = function () {"
            + "  try{document.getElementsByClassName('test')[0].style.color='red';}catch(e){}"
            + "};", null);
    } else {
        webView.loadUrl("javascript:"
            + "var FunctionOne = function () {"
            + "  try{document.getElementsByClassName('test')[0].style.color='red';}catch(e){}"
            + "};");
    }

Enable Javascript for your webview by adding the following line

wb.getSettings().setJavaScriptEnabled(true);

Android - How to use Javascript in an Android WebView?

Based on the Binding JavaScript documentation

Note: The object that is bound to your JavaScript runs in another thread and not in the thread in which it was constructed.

You are starting the activity on non-UI thread. You should run it on UI thread as follows:

@android.webkit.JavascriptInterface
    public void changeActivity(){
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                 Intent i = new Intent(MainActivity.this, JavascriptInterfaceActivity.class);
                 i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                 startActivity(i);
                 finish();
            }
        });

    }

Alternatively you can also use Handler.

Using JavaScript in Android Webview