[Qt-interest] can not set Layout correctly

[Tony Rietwyk]

Hi Bo and Yangzhi, 

This line is still going to cause problems, if the ancestor class has
already set a layout: 

> mHLayout = new QHBoxLayout(this);

Normally, I would do:

mHLayout = new QHBoxLayout();
...

delete layout();
setLayout( mHLayout );

But in this strange case, Yangzhi needs to do: 

setLayout( 0 );
setLayout( mHLayout );


Yangzhi - your first example should have shown a Qt warning for not being
able to set the second layout.  Do not ignore Qt warnings!  

Tony.