Porting to Qt 4

QPtrList<T>

QPtrList<T>, QPtrListIterator<T>, and QPtrListStdIterator<T> have been moved to the Qt3Support library. They have been replaced by the more modern QList and QLinkedList classes and their associated iterator classes.

When porting to Qt 4, you have the choice of using QList<T> or QLinkedList<T> as alternatives to QValueList<T>. QList<T> has an index-based API and provides very fast random access (QList::operator[]), whereas QLinkedList<T> has an iterator-based API.

The following table summarizes the API differences between QPtrList<T> and QList<T *>:

Remarks:

1. QPtrList::toVector(QGVector *) can be replaced by QVector::resize() and qCopy().

   For example, if you have code like

           QPtrList<QWidget> list;
           ...
           QPtrVector<QWidget> vector;
           list.toVector(&vector);

   you can rewrite it as

           QList<QWidget *> list;
           ...
           QVector<QWidget *> vector;
           vector.resize(list.size());
           qCopy(list.begin(), list.end(), vector.begin());

2. QPtrList::sort() relied on the virtual comparedItems() to sort items. In Qt 4, you can use qSort() instead and pass your "compare item" function as an argument.
3. QPtrList::find(const T *) returns an iterator, whereas QList::indexOf(T *) returns an index. To convert an index into an iterator, add the index to QList::begin().
4. QPtrList::removeFirst() and QPtrList::removeLast() return a bool that indicates whether the element was removed or not. The corresponding QList functions return void. You can achieve the same result by calling QList::isEmpty() before attempting to remove an item.

If you use QPtrList's auto-delete feature (by calling QPtrList::setAutoDelete(true)), you need to do some more work. You have two options: Either you call delete yourself whenever you remove an item from the container, or you can use QList<T> instead of QList<T *> (i.e. store values directly instead of pointers to values). Here, we'll see when to call delete.

The following table summarizes the idioms that you need to watch out for if you want to call delete yourself.

        list.replace(index, value);

        delete list[index];
        list[index] = value;

        list.removeFirst();

        delete list.takeFirst();

        list.removeLast();

        delete list.takeLast();

        list.remove(index);

        delete list.takeAt(index);

        list.remove(value);

        int i = list.indexOf(value);
        if (i != -1)
            delete list.takeAt(i);

        list.remove();

        QMutableListIterator<T *> i;
        ...
        delete i.value();
        i.remove();

        list.clear();

        while (!list.isEmpty())
            delete list.takeFirst();

        qDeleteAll(list);
        list.clear();

Be aware that QPtrList's destructor automatically calls clear(). If you have a QPtrList data member in a custom class and use the auto-delete feature, you will need to call delete on all the items in the container from your class destructor to avoid a memory leak.

QPtrList had the concept of a "current item", which could be used for traversing the list without using an iterator. When porting to Qt 4, you can use the Java-style QListIterator<T *> (or QMutableListIterator<T *>) class instead. The following table summarizes the API differences:

Be aware that QListIterator has a different way of iterating than QPtrList. A typical loop with QPtrList looks like this:

        QPtrList<QWidget> list;
        ...
        while (list.current() != 0) {
            do_something(list.current());
            list.next();
        }

Here's the equivalent QListIterator loop:

        QList<QWidget *> list;
        ...
        QListIterator<QWidget *> i(list);
        while (i.hasNext())
            do_something(i.next());

Finally, QPtrListIterator<T> must also be ported. There are no fewer than four iterator classes that can be used as a replacement: QList::const_iterator, QList::iterator, QListIterator, and QMutableListIterator. The most straightforward class to use when porting is QMutableListIterator<T *> (if you modify the list through the iterator) or QListIterator<T *> (if you don't). The following table summarizes the API differences:

Again, be aware that QListIterator has a different way of iterating than QPtrList. A typical loop with QPtrList looks like this:

        QPtrList<QWidget> list;
        ...
        QPtrListIterator<QWidget> i;
        while (i.current() != 0) {
            do_something(i.current());
            i.next();
        }

Here's the equivalent QListIterator loop:

        QList<QWidget *> list;
        ...
        QListIterator<QWidget *> i(list);
        while (i.hasNext())
            do_something(i.next());

Finally, QPtrListStdIterator<T> must also be ported. This is easy, because QList also provides STL-style iterators (QList::iterator and QList::const_iterator).

        queue.dequeue();

        delete queue.dequeue();

        queue.remove();

        delete queue.dequeue();

        queue.clear();

        while (!queue.isEmpty())
            delete queue.dequeue();

        qDeleteAll(queue);
        queue.clear();

        stack.pop();

        delete stack.pop();

        stack.remove();

        delete stack.pop();

        stack.clear();

        while (!stack.isEmpty())
            delete stack.pop();

        qDeleteAll(stack);
        stack.clear();

        vect.insert(i, ptr);

        delete vect[i];
        vect[i] = ptr;

        vect.remove(i);

        delete vect[i];
        vect[i] = 0;

        T *ptr = vect.take(i);

        T *ptr = vect[i];
        vect[i] = 0;

        vect.resize(n)

        while (n > vect.size())
            vect.append(0);
        while (n < vect.size() {
            T *ptr = vect.last();
            vect.remove(vect.size() - 1);
            delete ptr;
        }

        vect.clear();

        for (int i = 0; i < vect.size(); ++i)
            T *ptr = vect[i];
            vect[i] = 0;
            delete ptr;
        }

        qDeleteAll(vect);
        vect.clear();

        class VolumeControl : public QWidget, public QRangeControl
        {
            ...
        protected:
            void valueChange() {
                update();
                emit valueChanged(value());
            }
            void rangeChange() {
                update();
            }
            void stepChange() {
                update();
            }
        };

        class VolumeControl : public QAbstractSlider
        {
            ...
        protected:
            void sliderChange(SliderChange change) {
                update();
                if (change == SliderValueChange)
                    emit valueChanged(value());
            }
        };

        struct Shared
        {
            Shared() : count(1) {}
            void ref() { ++count; }
            bool deref() { return !--count; }
            uint count;
        };

    QVBox *vbox = new QVBox;
    QPushButton *child1 = new QPushButton(vbox);
    QPushButton *child2 = new QPushButton(vbox);

    QWidget *vbox = new QWidget;
    QPushButton *child1 = new QPushButton;
    QPushButton *child2 = new QPushButton;

    QVBoxLayout *layout = new QVBoxLayout;
    layout->addWidget(child1);
    layout->addWidget(child2);
    vbox->setLayout(layout);