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Thread: Get signal sender

  1. #1
    Join Date
    Oct 2019
    Qt products

    Default Get signal sender


    I use PureBasic, which uses Qt for its GUI implementation on Linux. While PureBasic provides access to a measure of the Qt API, it doesn't give everything I need, so I'm developing a shared library I can use with my program to make use of more of what it offers.

    I connect signals to the PureBasic 'gadgets' like this:
    Qt Code:
    1. qApp->connect(header, &QHeaderView::sectionClicked, header, &ListIconHeaderClicked)
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    In this example, I am trying to detect when the header of PureBasic's ListIconGadget, which uses QTreeWidget, is clicked.

    I'm not sure how I could use classes in this situation, since I know you can use QObject::sender() to get the signal sender. Is there a way I can find out which widget send the signal in the ListIconHeaderClicked(int logicalIndex) function?

    Thank you.

  2. #2
    Join Date
    Jan 2008
    Alameda, CA, USA
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    Qt products

    Default Re: Get signal sender

    qApp->connect(header, &QHeaderView::sectionClicked, header, &ListIconHeaderClicked)
    This is incorrect syntax for a connect() statement. The first half is OK - you are saying you want to connect to an instance of the QHeaderView class ("header") and its sectionClicked() signal. The second half is wrong for two reasons: first, if you want to handle that signal in some other class that you have implemented, then you put the instance pointer for that class as the third argument (not "header"); and second, the next argument must be the address of a method for the class you used as the third argument:

    Qt Code:
    1. connect( header, &QHeaderView::sectionClicked, myClass, &MyClass::onSectionClicked ); // or whatever you call your class and slot
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    Calling connect() through a qApp pointer is not necessary unless you are doing it from some code that is not in a class derived from QObject. QObject implements the connect() methods and all derived classes inherit them. Your slot definition should look like this:

    Qt Code:
    1. class MyClass : public SomeClassDerivedFromQObject
    2. {
    3. Q_OBJECT
    5. // constructor, destructor, etc.
    7. public slots:
    8. void onSectionClicked( int logicalIndex );
    9. };
    11. void MyClass::onSectionClicked( int logicalIndex )
    12. {
    14. // do whatever you want with the header and index.
    15. // If you need the pointer to the QHeaderView:
    17. QHeaderView * pView = qobject_cast< QHeaderView * >( sender() );
    18. if ( pView != nullptr )
    19. {
    20. // Safe to use the pView pointer
    21. }
    22. }
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    Last edited by d_stranz; 5th November 2019 at 21:24.
    <=== The Great Pumpkin says ===>
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