How to use addView to add view to layout?

I can't remember, but maybe there is any "refresh" method to load again the layout.

Try layout.invalidate();

You forgot to specify the LayoutParameters for the newly added view.

LinearLayout layout = (LinearLayout)findViewById(R.id.mainLayout);
    TextView text=new TextView(this);
    text.setLayoutParams(new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
    text.setText("test");
    layout.addView(text);

EDIT

The GridView with an id of @+id/gridview is defined with a layout height of fill_parent, leaving you with no space to add a new view. Changing its height to wrap_content may solve your problem.

Adding my comment to this post to help others easily verify the solution.