Issue with programming a function template to list the QWidgets in a QDialog with a specific type

[PALYGAP]

In the creator function of my Qdialog class, I got that code to work find :

QList<QComboBox *> CombList2;
   QString QCBName;
   for(int i=1;; i++ )
   {
       QCBName = "comboBox_" + QString::number(i);
       if( ui->gridLayoutWidget->findChild<QComboBox *>( QCBName ) != NULL )
       {
           CombList2.append(ui->gridLayoutWidget->findChild<QComboBox *>( QCBName ) );
       }
       else {
           break;
       }
   }

It constructs an ordered Qlist with QComboBox that are in my UI. The name of the QComboBox in the ui are comboBox_1, comboBox_2 ... and the comboBox numbers have been set to match the ordered fashion in which they appear in the UI.

This actually replaces this :

   QComboBox *l_TheComboBoxs[NUMofKNOBS_BCR2000] = { ui->comboBox_1, ui->comboBox_2, ui->comboBox_3, ui->comboBox_4, ui->comboBox_5, ui->comboBox_6, ui->comboBox_7, ui->comboBox_8,
                                     ui->comboBox_9, ui->comboBox_10, ui->comboBox_11, ui->comboBox_12, ui->comboBox_13, ui->comboBox_14, ui->comboBox_15, ui->comboBox_16,
                                     ui->comboBox_17, ui->comboBox_18, ui->comboBox_19, ui->comboBox_20, ui->comboBox_21, ui->comboBox_22, ui->comboBox_23, ui->comboBox_24,
                                     ui->comboBox_25, ui->comboBox_26, ui->comboBox_27, ui->comboBox_28, ui->comboBox_29, ui->comboBox_30, ui->comboBox_31, ui->comboBox_32
                                    };

I wanted to build a function that would do the same for deferent widgets QComboBox, QLabel, QDial, QSlidder ..

I tried with this :

template <class T>
void fillQWidgetList(QList<T> *QWidgetList, QWidget *gridLayoutWidget, Q_Widget_Type qwidgettype, QRegExp *QWidgetName)
{
    QString QCBName;
    for(int i=1;; i++ )
    {
        //QCBName = &QWidgetName + QString::number(i);
        if( qwidgettype == Q_Combo_Box || gridLayoutWidget->findChild<T *>( QCBName ) != NULL )
        {
            QWidgetList->append( gridLayoutWidget->findChild<T *>( QCBName ) );
        }
        else {
            break;
        }
    }
}

but compiler issue an error when I call the function for QDialogBox

fillQWidgetList<QComboBox>( &CombList2, ui->gridLayoutWidget, Q_Combo_Box, &Exp);

error : no matching function for call to 'BCR2000::fillQWidgetList(QList<QComboBox*>, QWidget&, Q_Widget_Type, QRegExp*)'
fillQWidgetList<QComboBox>( &CombList2, ui->gridLayoutWidget, Q_Combo_Box, &Exp);
^
I not sure what this means "QWidget*&". Anybody has experience with function template an this kind of issue

[A Former User]

Hi!
@PALYGAP said in Issue with programming a function template to list the QWidgets in a QDialog with a specific type:

template <class T>
void fillQWidgetList(QList<T> *QWidgetList, QWidget *gridLayoutWidget, Q_Widget_Type qwidgettype, QRegExp *QWidgetName)

First thing: Don't give your own parameters / variables etc names starting with a "q" or "Q". In the context of a Qt based program that's highly misleading. E.g. you have a parameter named QWidgetList. Everyone would think that this is a Qt class (it looks similar to QListWidget).

Second thing: Don't pass arguments by raw pointer unless you have a reason to do so. So, instead of QList<T> *widgetList better use a reference: QList<T> &widgetList.

Third thing:
You have a typo: void fillQWidgetList(QList<T> ... has to be void fillQWidgetList(QList<T*>.

[PALYGAP]

Thanks @Wieland for the advices.

I've cleaned up the code and use references in the function call, and got a version of the code that compiles :

****FUNCTION CALL****
    QString widgetName = "comboBox_";
    QList<QComboBox *> CombList;
    fillWidgetList<QComboBox>( &CombList, &ui->gridLayoutWidget, &widgetName);

****FUNCTION****
template <class T>
void MIDIControllerGenericDialog::fillWidgetList( QList<T *> *dialogWidgetList, QWidget **gridLayoutWidget, QString *widgetName )
{
    QString QCBName;
    for(int i=1;; i++ )
    {
        QCBName = *widgetName + QString::number(i);
        if( (*gridLayoutWidget)->findChild<T *>( QCBName ) != NULL )
        {
            dialogWidgetList->append( (*gridLayoutWidget)->findChild<T *>( QCBName ) );
        }
        else {
            break;
        }
    }
}

but there is a linking issue " error : undefined reference to `void MIDIControllerGenericDialog::fillWidgetList<QComboBox>(QList<QComboBox*>, QWidget**, Widget_Type, QString)'

The calling calling function is in the constructor of my BCR2000 class and the BCR2000 class inherit from the MIDIControllerGenericDialog class where the fillWidgetList is defined :

class MIDIControllerGenericDialog : public QDialog
{
    Q_OBJECT

public:
    explicit MIDIControllerGenericDialog(QWidget *parent = 0);
    ~MIDIControllerGenericDialog();

    void storeGeom(void);

    template <class T>
    void fillWidgetList( QList<T *> *dialogWidgetList, QWidget **gridLayoutWidget, Widget_Type widgetType, QString *widgetName );

Putting the function in the BCR2000 class solves the linking issue. Weird and problematic since I want to move functions from the BCR2000 class to the MIDIControllerGenericDialog class.

[PALYGAP]

Solved the linking problem. Template function definition has to be in the header file (.h) so that the linker works properly. Seems a fairly common issue : see THIS for the explanation.

Thanks again @Wieland for the help.

[PALYGAP]

One thing I am wondering now : wouldn't it be better to use a single function that takes a QList of QObject :

void MIDIControllerGenericDialog::fillWidgetList( QList<QObject *> *dialogWidgetList, QWidget **gridLayoutWidget, QString *widgetName )

since the important function used in the fillWidgetListfunction is QObject::findchild() (and it works on QObjects)
and feed it with casted reference (or pointer ) like so :

    QString widgetName = "comboBox_";
    QList<QComboBox *> CombList;
    fillWidgetList( (QObject>) &CombList, &ui->gridLayoutWidget, &widgetName);

Not sure if that would work. Anybody tried that ?

[jsulm]

@PALYGAP Did you try it?
It will not compile because QList<QObject *> is not the same as QList<QComboBox *>.

[PALYGAP]

No I haven't.

ctually if the both the function call and the function definition uses QObject instead of QComboBox it should compile, shouldn't it ?