White Bar occurs in the actionBar

I ran in to the same thing and did the following.

I opened the activity_main layout in the designer and deleted each item I didn't want (the bit white bar at the top and some email looking icon), which was accomplished by simply clicking on them to ensure they were highlighted and then and then clicked the delete button.

After this, I opened up the main_activity.java file and removed all methods with the exception of the onCreate method.

After doing this, I ran my app and had a completely blank full screen view.

I did so and it worked for me:

in XML design view I deleted objects, which I didn't want. in java file I deleted all things which was connected to this toolbar and fab:

   Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });

The problem, why bob had white screen was because you had no set content view and deleted it with onCreate method. That's why was no any contentView. I don't know Java, I learn everything from this tutorial, maybe there are some different solutions too, but this worked for me