Qt designer: How to add widget to a layout in the designer when the layout appears infinitely thin ?

Add widget to a layout in the designer:

  By choosing the layout and drop the widget is used to  select item in the Object of controller pane. And to  select the layout on the actual form  and the object is  auditor pane.

The alternative answer is :

They used to  select the  workaround to display the structure board and to  select the layout  the top or bottom margins  value 20  and then drag the  basic into the layout .