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

Wieland

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 ?