Android Web-View : Inject local Javascript file to Remote Webpage

Question

It has been asked many times before, I browsed through everything, no clear answers yet.

Question simplified: Is it possible to inject local Javascript file (from asset or storage) to remote webpage loaded in an Android Web-View? I know that it is possible to inject such files to local Webpages (Assets HTML) loaded in a Web-View.

Why do I need this to work? : To make browsing experience faster, by avoiding downloading of bigger files such as Js and CSS files every time. I want to avoid Web-View Caching.

Answer 1

loadUrl will work only in old version use evaluateJavascript

webview.evaluateJavascript("(function() { document.getElementsByName('username')[0].value='USERNAME';document.getElementsByName('password')[0].value='PASSWORD'; "+
"return { var1: \"variable1\", var2: \"variable2\" }; })();", new ValueCallback<String>() {
                @Override
                public void onReceiveValue(String s) {
                    Log.d("LogName", s); // Prints: {"var1":"variable1","var2":"variable2"}
                }
            });

Answer 2

Yes, you could use shouldInterceptRequest() to intercept remote url loading and return local stored content.

WebView webview = (WebView) findViewById(R.id.webview);

webview.setWebViewClient(new WebViewClient() {
    @Override
    public WebResourceResponse shouldInterceptRequest (final WebView view, String url) {
       if (url.equals("script_url_to_load_local")) {
           return new WebResourceResponse("text/javascript", "UTF-8", new FileInputStream("local_url")));
       } else {
           return super.shouldInterceptRequest(view, url);
       }
    }
});

Answer 3

Be careful using evaluateJavascript: if there is a syntax error or exception thrown in your javascript it will call your onReceiveValue with a null. The most common way to support both SDK 19 as well as lower seems to be like this:Fill form in WebView with Javascript

Also if you get terribly desperate for some kind of browser functionality (in my case, never could figure out how to get DRM to work well) you could use a bookmarklet within normal chrome, which works only if you type the bookmark name into the omnibox but does work and does inject javascript.

Also be aware that with the default WebView you can't use javascript alerts to test anything, they don't show. Also be aware that "video" by default (like html <video> tags) doesn't "really work" by default and also DRM video doesn't work by default, they're all configure options :\