在onpostexecute（）中打开浏览器

Question

我想从asynctask中打开onpostexecute中的浏览器。但是在开始我的活动时我得到了一个nullpointerexception：

我的代码：

@Override
    protected void onPostExecute(String file_url) {
            AlertDialog alertDialog = new AlertDialog.Builder(context).create();
    alertDialog.setTitle("Details");

        ScrollView scrollview = new ScrollView(context);
        LinearLayout lila1= new LinearLayout(context);
        lila1.setOrientation(1); //1 is for vertical orientation;

        lila1.setBackgroundColor(android.graphics.Color.BLACK);
        scrollview.setBackgroundColor(android.graphics.Color.BLACK);

            final Button adv1 = new Button(context);
            adv1.setOnClickListener(new View.OnClickListener() {

@Override
                public void onClick(View v) {
                     Uri uriUrl = Uri.parse("http://androidbook.blogspot.com/");
                 Intent launchBrowser = new Intent(Intent.ACTION_VIEW, uriUrl);
                startActivity(launchBrowser); //<- does not work

                }
            });
            lila1.addView(adv1);