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Thread: Inheriting QListViewItem

  1. #1
    Join Date
    Feb 2006
    Qt products
    Qt3 Qt4
    Unix/X11 Windows

    Default Inheriting QListViewItem

    I have a class which inherits QListViewItem.
    class myItem : public QListViewItem
    void somefunction();
    now I create a list view "mainList" from Qt Designer and add my items in this way
    myItem *item=new myItem(mainList,"label");
    however when I try to fetch the item by iterating the listview why wouldn't the following code work
    myItem *item=mainList->firstChild();
    //this creates an error : InValid conversion from QListViewItem to myItem

    but if I do
    QListViewItem *item=mainList->firstChild();
    then it is ok but I can't call someFunction() which is inside myItem
    I know the working solution is :
    myItem *item=(myItem *) mainList->firstChild();
    but I am wondering if myItem inherits QListViewItem then it "is a" QListViewItem why do we still need to typecast. Shouldn't the "is a " relationship of inheritence hold true here ?

    Thank you to anyone who would like to solve this small query.
    Humans make mistake because there is really NO patch for HUMAN STUPIDITY

  2. #2
    Join Date
    Mar 2006
    The Netherlands
    Thanked 29 Times in 29 Posts
    Qt products
    Qt3 Qt4

    Default Re: Inheriting QListViewItem

    It is true that myItem is a QListViewItem. But not necessarily the other way around. The QListView holds QListViewItems, and knows nothing about myItems. So you have to downcast. It might be a good idea to subclass QListView also, to support myItems, so you won't have to cast from the outside.
    "The strength of a civilization is not measured by its ability to wage wars, but rather by its ability to prevent them." - Gene Roddenberry

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