Invalid use of incomplete type 'class Ui::MainWindow' in default Qt Creator Hello world with QTabWidget added to mainwindow.ui

[enjoysmath]

To recreate:

1. Create a new Qt Widgets application with a mainwindow.ui form and class etc.
2. Add a QTabWidget from the form designer to the canvas (QMainWindow)
3. Right-click on the QTabWidget and Layout > On a Grid.
4. The default name is tabWidget as you can see in the properties panel. Leave the name alone.
5. Create a member function in your QMainWindow class (the class template was already generated by Qt in step 1).
6. Within that function, call ui->tabWidget.

The line should be highlighted red indicating errors but you can also see it when you build in the build error output panel.

invalid use of incomplete type 'class Ui::MainWindow'

Is the first error, and other places when they don't say this will say that tabWidget is not a member of ui. So how do you access ui's members as created in the form designer?

[enjoysmath]

This post is deleted!

[enjoysmath]

Found reason: You can't do that addTabWidget definition in the class declartion, because of C++ limitation of forward class declarations I can only call ui->tabWidget in a .cpp defined function.

[JonB]

@enjoysmath
Please paste (not screenshot) the .cpp file you show, at least up to line #20. We need to see the i#includes at the start.

Similarly, paste from your mainwindow.h, at least up to line #22-ish.

[VRonin]

@enjoysmath said in Invalid use of incomplete type 'class Ui::MainWindow' in default Qt Creator Hello world with QTabWidget added to mainwindow.ui:

Found reason: You can't do that addTabWidget definition in the class declartion, because of C++ limitation of forward class declarations I can only call ui->tabWidget in a .cpp defined function.

This is not accurate, you can use it wherever you want but you have to #include "ui_mainwindow.h" first

[nokede2571]

This post is deleted!