Override current Javascript functions with Android Webview

Question

I'm porting my website to Android, and using an Webview to show the content to user. There are a lot of Javascript functions in my website, and I want to intercept them. I already seen a "solution" here.

However, I think there should be a more proper way, using Javascript Interface:

this.webView.addJavascriptInterface(this.webJavascriptInterface, "Android");

This way, I have to modify my website to call both myFunction() and Android.myFunction(). I tried to leave a blank String in the interface:

this.webView.addJavascriptInterface(this.webJavascriptInterface, "");

but the result was as I guess, it couldn't work. Is there a way to override current Javascript functions in Webview?

Answer 1

// android
webView.setWebViewClient(new WebViewClient() {
    @Override
    public void onPageFinished(WebView view, String url) {
        super.onPageFinished(view, url);
        webView.loadUrl("javascript:function inputClick(val){native.abcd(val);}");     // override js function
    }
});

webView.loadUrl("file:///android_asset/test.html");

webView.addJavascriptInterface(new Object() {
    @JavascriptInterface
    public void abcd(int val) {
        Log.e(TAG, "#js abcd" + val);
    }
}, "native");

<!-- html -->
<input type="button" onclick="inputClick(2)" value="button">

== add some explain at Sep 07,2015

because javascript function could be override, so you can override javascript function while page finished.

if not, normal implement maybe like this:

// js code
function inputClick(val) {
    native.abcd(val); // native and abcd defined in WebView method addJavascriptInterface
}

but this normal implement is seems not work in iOS(Object-C), and must edit HTML page. is just move the java-javascript bridge code from HTML to Java. (see method onPageFinished in example code)

Answer 2

You can do this by injecting a new javascript that redefines old function, basically you can override existing function with this.

For example, to override window.print() function, I use this

webView.loadUrl("javascript:window.print = function() {Android.printPage();}")