Android JS in WebView.loadUrl()

Issue

I want to load a webpage in WebView but remove parts of the webpage. So, I created a custom WebViewClient. And, in onPageFinished(), I did some javascript to remove some elements. Then, I made the WebView visible.

However, when I run it, it sets the view visible, and then I see the elements being removed. It is as if the JS is running in the background very slowly. It creates a poor viewing experience because it flashes the full page and then the desired partial page.

Here is my onPageFinished()

@Override
public void onPageFinished(WebView view, String url) {

    view.loadUrl("javascript:"
            + "document.getElementsByClassName('header')[0].style.display='none';"
            + "document.getElementById('section_0').style.display='none';"
            + "document.getElementById('page-actions').style.display='none';"
            + "document.getElementsByClassName('languageSelector')[0].style.display='none';"
            + "document.getElementById('mw-mf-last-modified').style.display='none';"
            + "document.getElementById('footer').style.display='none';");

    loadingView.setVisibility(View.INVISIBLE);
    view.setVisibility(View.VISIBLE);
}

Any ideas on how to fix this?

Solution

In onPageFinished():

view.loadUrl("javascript:"
            + "var FunctionOne = function () {"
            + "  var r = $.Deferred();"
            + "  try{document.getElementsByClassName('header')[0].style.display='none';}catch(e){}"
            + "  try{document.getElementById('section_0').style.display='none';}catch(e){}"
            + "  try{document.getElementById('page-actions').style.display='none';}catch(e){}"
            + "  try{document.getElementsByClassName('languageSelector')[0].style.display='none';}catch(e){}"
            + "  try{document.getElementById('mw-mf-last-modified').style.display='none';}catch(e){}"
            + "  try{document.getElementById('footer').style.display='none';}catch(e){}"
            + "  setTimeout(function () {"
            + "    r.resolve();"
            + "  }, 2500);"
            + "  return r;"
            + "};"
            + "var FunctionTwo = function () {"
            + "  window.CallToAnAndroidFunction.setVisible();"
            + "};"
            + "FunctionOne().done(FunctionTwo);");

In MainActivity.onCreate():

this.webView.addJavascriptInterface(new JsObject(webView, loadingView), "CallToAnAndroidFunction");

In MainActivity():

public class JsObject {
    private View loadingView;
    private View view;
    JsObject(View view, View loadingView){this.view = view;this.loadingView = loadingView;}
    @JavascriptInterface
    public void setVisible(){
        runOnUiThread(new Runnable() {

           @Override
           public void run() {
               view.setVisibility(View.VISIBLE);  
                loadingView.setVisibility(View.INVISIBLE);               
           }
       });
    }
}

So, it was a combination of making a JavascriptInterface and making a JS function to wait for the JS calls to finish before calling the interface (with the visibility settings).

Answered By - Eric Cochran