I got it wrong, can't compile

[been_1990]

Sorry about it, terrible mistake. I confused myself.
About the uninitialized variable, this is how the ICS video wrote the code:

ListDelegate delegate;
    QListView view;
    view.setItemDelegate(&delegate);
    view.show();

ListDelegate delegate;
    QListView view;
    view.setItemDelegate(&delegate);
    view.show();

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Which does not compile and outputs:

F:\Documents\QT Projects\QListView_test/main.cpp:8: undefined reference to `ListDelegate::ListDelegate(QObject*)'
:-1: error: collect2: ld returned 1 exit status

F:\Documents\QT Projects\QListView_test/main.cpp:8: undefined reference to `ListDelegate::ListDelegate(QObject*)'
:-1: error: collect2: ld returned 1 exit status

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And the ListDelegate class is written exactly as the video. But you are definitely right about my C++ skills...