Rendering Android webview to bitmap, html5 javascript , callback issue

Question

I have an activity with a button and an image and a webview. My goal is to load a page, then execute javascript on it to draw graphics using HTML5 etc.

The height of the image drawn by the html5 is unknown/variable , but the width should always be the same as the phone's width/or browser window.

I have a javascript interface to get a callback containing info that it has now finished calling the drawing function, and it is giving me the height.

Here is the setup of the web-view

mWeb = (WebView) findViewById(R.id.webView1);
mWeb.clearCache(true);
mWeb.addJavascriptInterface(new IJavascriptHandler(), "cpjs");

mWeb.getSettings().setJavaScriptEnabled(true);

mWeb.loadUrl(" http://theURL.com ");
mWeb.setInitialScale(100);
mWeb.getSettings().setDefaultZoom(WebSettings.ZoomDensity.FAR);


mWeb.setWebViewClient(new WebViewClient() {
            public void onPageFinished(WebView view, String url){
                mWidth = mWeb.getWidth();
                mHeight = mWeb.getHeight();

                view.loadUrl("javascript: Tools.adjustWidth(" + mWidth + " )");

                String javaCouponRender = "renderCoupon(" + kupongJson + ", 0); void(0)";
                view.loadUrl("javascript: " + javaCouponRender);

            }
             });



        }

And the button I have in my view, I have used to initiate render my webview to a texture with this function:

void renderCoupon(int width,int height){


    bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    final Canvas c =new Canvas(bitmap);
    mWeb.draw(c);
    imgView.setMinimumWidth(width);
    imgView.setMinimumHeight(height);
    imgView.setImageBitmap(bitmap);
    imgView.setVisibility(View.VISIBLE);
}

This works. Pressing the button, renders the drawn content to the texture and the imageview has a correct result. The only cavaet is I have to wait until the page has loaded/drawn before pressing the button.

Now, I have implemented the callback I get from javascript like this:

final class IJavascriptHandler {
       IJavascriptHandler() {
       }

       public void couponRenderedCallback(final int height){

           mHasGotRenderCallback = true;
           mHeight = height;
              Toast t = Toast.makeText(getApplicationContext(), "see if it helps sleeping", 2000);
              t.show();
              try{
                Thread.sleep(5000);
            }
            catch(InterruptedException ex){

            }
              runOnUiThread(new Runnable() {
                    @Override
                    public void run() {

                        Toast t2 = Toast.makeText(getApplicationContext(), "and now we render to texture", 2000);
                        t2.show();       
                        renderCoupon(mWidth, mHeight);
                    }
                });

       }

    }

And every time, this callback function renders a white page. The funny thing is that if I physically press the render-to-texture button as soon as I see this callback is called, it shows the expected result. Is it runOnUiThread that is failing somehow?

The sleep is something I added to see if there was some sort of funny delay of the webview rendering and the callback I get from javascript.

I have also tried moving the sleep into the runOnUiThread , which also did not help.

I hope someone knows in what direction I should look to solve this problem. Any help is appreciated.

Answer 1

Found a solution, which was to change the renderCoupon to this:

void renderCoupon(final int width,final int height){

    mWeb.postDelayed(new Runnable() {

        @Override
        public void run() {
            // TODO Auto-generated method stub
            bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
            final Canvas c =new Canvas(bitmap);
            mWeb.draw(c);

            imgView.setMinimumWidth(width);
            imgView.setMinimumHeight(height);
            imgView.setImageBitmap(bitmap);
            imgView.setVisibility(View.VISIBLE);
        }
    }, 100);
}

And of course I removed the Sleep stuff in my callback. Thanks to my collegue who tipped me about this. :)