That's a bad idea. Each tab should be in each own class.
I agree totally with you. I am just saying that if you use Qt Designer to build GUI, you get only one GUI class for all tabs when using QTabWidget. So there is a way to assign different classes to different tabs?
I think that I must do following then:

1. Make GUI class for each desired tab.
2. Design GUI part of each class (can be done with Designer too).
3. Then assign these GUI classes to each tabs (I think this must be done with code, because Designer doesnt support it).

Am I correct here?