Need advise on memory management/garbage collection in QAbstractListModel

[scotryder]

Hi there,

I'm very new to QT and coming from java memory management is overwhelming for me.

Here is my plan

im going to make a QAbstractListModel model, ill use a QList<MyVOObject*> where ill new MyVOObject() and add back to QList. That QList will be use as "source" qlist and ill filter objects from this list and put them in a second list that will appear on ListView. For example show all objects or objects by a single country.

My question is what pointer should i use? i read somewhere about QSharedPointer but then somewhere i heard that use C++ shared_ptr

Please advise
Thanks

[sierdzio]

@scotryder said in Need advise on memory management/garbage collection in QAbstractListModel:

That QList will be use as "source" qlist and ill filter objects from this list and put them in a second list that will appear on ListView. For example show all objects or objects by a single country.

You can use QSortFilterProxyModel for that.

My question is what pointer should i use? i read somewhere about QSharedPointer but then somewhere i heard that use C++ shared_ptr

It does not matter which you choose, pick one that you prefer. QSharedPointer has an advantage of being a Qt class with nice API. shared_ptr is slightly more performant and you'll learn standard C++ API when you use it.

[scotryder]

@sierdzio
Thank you very much :)
I might have questions regarding integrating it in QML but will post a new question.

[VRonin]

@scotryder said in Need advise on memory management/garbage collection in QAbstractListModel:

I might have questions regarding integrating it in QML

In this case, don't implement QAbstractListModel which is fairly hard, declare MyVOObject as a meta type (if it's not a QObject) and use QStandardItemModel. see this wiki page for an example

[scotryder]

@VRonin Thanks will look into that :)

[sierdzio]

@VRonin said in Need advise on memory management/garbage collection in QAbstractListModel:

In this case, don't implement QAbstractListModel which is fairly hard

It's just a matter of reimplementing data(), roleNames() and setData(), nothing too taxing ;-) Anyway, cool link with QStandardItemModel, thanks for sharing.

[VRonin]

@sierdzio and insertRows() and removeRows() (using begin and end methods) and buddy() (the one I always forget about)

[sierdzio]

@VRonin said in Need advise on memory management/garbage collection in QAbstractListModel:

@sierdzio and insertRows() and removeRows() (using begin and end methods) and buddy() (the one I always forget about)

These do not need to be implemented, unless you actually need them for something. Model will work fine without these methods.

Anyway, we're derailing the topic a bit, sorry @scotryder :D

[scotryder]

@sierdzio

Ok i created a child class of QSortFilterProxyModel and exposed it to QML, but how do i assign my DataModel (already exported to QML as Class)?

ListView{

model: MySortProxy{

//which property to assing my dataModel

}

}

Sorry, its sourceModel

[VRonin]

@sierdzio I like derailing. I think you still need rowCount() reimplemented and I'm not sure you can live without buddy()

@scotryder

child class of QSortFilterProxyModel

Not sure what you mean by "child" here.

[scotryder]

Ok thanks to you both, i finally managed to make my FilterProxyRun (without overrding any methods obviously :P )

Now my main problem is, how do i apply filters based on multiple fields of my Person class?
for example, i want to filter list of people by applying filters on age, name, location etc.

So which method should i override and how i apply multiple filters on roles at once.

Thanks

[sierdzio]

This might help https://doc.qt.io/qt-5/qsortfilterproxymodel.html#filtering

[VRonin]

Base Class: header, source

This requires all filters to be satisfied:

#include "MultipleFilterProxy.h"
class AndFilterProxy : public MultipleFilterProxy
{
    Q_OBJECT
    Q_DISABLE_COPY(AndFilterProxy)
public:
    explicit AndFilterProxy(QObject *parent = Q_NULLPTR) : MultipleFilterProxy(parent)
{}
protected:
    bool filterAcceptsRow(int source_row, const QModelIndex & source_parent) const Q_DECL_OVERRIDE{    
        for (int i = 0; i < sourceModel()->columnCount(source_parent); ++i) {
            QModelIndex currntIndex = sourceModel()->index(source_row, i, source_parent);
            for (auto dateRngIter = m_dateRangeFilter.at(i).constBegin(); dateRngIter != m_dateRangeFilter.at(i).constEnd(); ++dateRngIter) {
                const QDate testDate = currntIndex.data(dateRngIter.key()).toDate();
                if (!((testDate >= dateRngIter.value().first || dateRngIter.value().first.isNull()) && (testDate <= dateRngIter.value().second || dateRngIter.value().second.isNull())))
                    return false;
                
            }
            for (auto boolIter = m_boolFilter.at(i).constBegin(); boolIter != m_boolFilter.at(i).constEnd(); ++boolIter) {
                const bool testBool = currntIndex.data(boolIter.key()).toBool();
                if (testBool != boolIter.value())
                    return false;
            }
            for (auto regExpIter = m_regExpFilter.at(i).constBegin(); regExpIter != m_regExpFilter.at(i).constEnd(); ++regExpIter) {
                if (regExpIter.value().first.match(currntIndex.data(regExpIter.key()).toString()).hasMatch() != regExpIter.value().second)
                    return false;
            }
        }
    return true;
}
};

This requires any filter to be satisfied:

#include "MultipleFilterProxy.h"
class OrFilterProxy : public MultipleFilterProxy
{
    Q_OBJECT
    Q_DISABLE_COPY(OrFilterProxy )
public:
    explicit OrFilterProxy(QObject *parent = Q_NULLPTR) : MultipleFilterProxy(parent)
{}
protected:
    bool filterAcceptsRow(int source_row, const QModelIndex & source_parent) const Q_DECL_OVERRIDE{    
        for (int i = 0; i < sourceModel()->columnCount(source_parent); ++i) {
            QModelIndex currntIndex = sourceModel()->index(source_row, i, source_parent);
            for (auto dateRngIter = m_dateRangeFilter.at(i).constBegin(); dateRngIter != m_dateRangeFilter.at(i).constEnd(); ++dateRngIter) {
                const QDate testDate = currntIndex.data(dateRngIter.key()).toDate();
                if (((testDate >= dateRngIter.value().first || dateRngIter.value().first.isNull()) && (testDate <= dateRngIter.value().second || dateRngIter.value().second.isNull())))
                    return true;
                
            }
            for (auto boolIter = m_boolFilter.at(i).constBegin(); boolIter != m_boolFilter.at(i).constEnd(); ++boolIter) {
                const bool testBool = currntIndex.data(boolIter.key()).toBool();
                if (testBool == boolIter.value())
                    return true;
            }
            for (auto regExpIter = m_regExpFilter.at(i).constBegin(); regExpIter != m_regExpFilter.at(i).constEnd(); ++regExpIter) {
                if (regExpIter.value().first.match(currntIndex.data(regExpIter.key()).toString()).hasMatch() == regExpIter.value().second)
                    return true;
            }
        }
    return false;
}
};

[scotryder]

@VRonin Thank you very much for such a detailed reply, u r a life saver :)