How to remove item from QQueue at index i.
Being that QQueue is based on and will work like a std::queue, which is a FIFO (First-in First-out container), it seems you may need to rethink your usage of QQueue.
To remove the head item, use
QQueue::dequeue()
To remove an item at index i (using QList inherited functions)
QQueue::removeAt( int i )
If you need to do this, rethink your QQueue usage please.
(see Qt Documentation)
QQueue inherits QList<T>, so you can use void QList::removeAt(index) inherited method.
Qt documentation for,
T QQueue::dequeue ()
states that, Removes the head item in the queue and returns it. This function assumes that the queue isn't empty.
Hope it helps.
Edit:
If you want to remove item from a specific index, use QList instead.
There are functions like,
void QList::removeAt ( int i )
and
T QList::takeAt ( int i )
which you can make use depending upon your need..
Related
I have read some topics here about signals and slots and its parameters but found nothing about following problem:
I am working with Qt 5.7
I simply have 2 classes, inside 1st, I want to emit signal with string message and location(or specific object) where to display it.
Now it is like this: I have 1st class where I emit signal :
emit signalWriteToTextEdit("hallo","textEdit_3");
What I want to do is somehow pass as the second argument an object like textEdit. No QString as its now.
Inside 2nd class is the slot:
void writeToTextEdit(QString info, QString where){
where.append(info); //I would like to do something like this
}
Just dont know how to consider that second parameter "where" as accessible object for example textEdit, so I could change its content.
I am thinking also if this is possible:
Is there some method for Ui object like finding elements by name?
Is it possible to go with foreach over all elements in ui and check their names...? I tried but dont know how to go through that.
If its not clear, I will explain more
After a little digging, I came across the QObject::findChild function. This will allow a string lookup recursively through the UI, those I am unsure of performance.
Edit for more detail:
Returns the child of this object that can be cast into type T and that is called name, or 0 if there is no such object. Omitting the name argument causes all object names to be matched. The search is performed recursively.
If there is more than one child matching the search, the most direct
ancestor is returned. If there are several direct ancestors, it is
undefined which one will be returned. In that case, findChildren()
should be used.
Just use QWidget* or QObject* (if it is not always a widget) as the argument type
signals:
void writeToTextEdit(const QString &what, QWidget *where)
or if it is always a QTextEdit even more specifically
signals:
void writeToTextEdit(const QString &what, QTextEdit *where)
Though it is not clear why the code needs to emit a signal if it has access to the target object, it could simply call setText directly
I want to delete a row which has children from a QTreeView. I use QAbstractItemModel's removeRow ( int row, const QModelIndex & parent = QModelIndex() ) method，pass the row and parent index of the deleted row. But this method returns false.
How can I delete a row which has children? Do I need write a method to recursively delete rows?
You should look at this: removeRow
This is a convenience function that calls removeRows(). The QAbstractItemModel implementation of removeRows() does nothing.
And here in QAbstractItemModel::removeRows():
The base class implementation does nothing and returns false.
If you implement your own model, you can reimplement this function if you want to support removing. Alternatively, you can provide your own API for altering the data.
I know I'm a bit late to the party, but I wanted to document this because I can't seem to find any good answer to the original question.
You need to implement QAbstractItemModel::removeRows in your model. There is a Qt example, Editable Tree Model, that shows how this should be done. The basic procedure is to call beginRemoveRows, delete the item(s), then call endRemoveRows.
Your tree item class should have a method for deleting a range of its child items. You call this method on the parent item from within your reimplementation of removeRows. The tree item class should be set up to delete its children when it is destroyed. The Qt example does this through the destructor, though with C++11 and later this is best done by storing children in a container of smart pointers so they get automatically deleted when the container goes out of scope.
You do not need to account for child items being collapsed or expanded in the tree view - QTreeView knows whether or not child items are visible or not and will update the view accordingly. In other words, if you delete a tree item with a few child items that were visible in the tree view, they will be automatically removed from the view. This is something that I can't find documented anywhere, but from personal experience I can say that it works (as long as you call beginRemoveRows and endRemoveRows correctly).
For QGraphicsScene::drawItems the reference says:
Reimplement this function to provide custom painting of all items for the scene; gaining complete control over how each item is drawn.
But this function is marked as obsolete.
Is there any new equivalent method?
QGraphicsView::paintEvent() now calls
d->scene->d_func()->drawItems()
which means the method is part of class QGraphicsScenePrivate which you cannot override afaik.
If you need to change the way your items are drawn, first try to think of another way (i.e. a solution which does not require stepping into the drawItems() method). If you can't find any solution like that, your only chance is reactivating the pre-4.6-behaviour by setting
QGraphicsView::setOptimizationFlag( QGraphicsView::IndirectPainting )
i noticed that QObject::children() method return a const reference to QObjectList, that contains the children of the qobject. Will it be safe to cast away the constness and sort the list with qSort?
Thanks
Anton
No, you should not do this. This is the definition of QObject::children():
inline const QObjectList &children() const { return d_ptr->children; }
This means you directly get the reference of the internal objectlist.
And the documentation says:
Note that the list order changes when
QWidget children are raised or
lowered. A widget that is raised
becomes the last object in the list,
and a widget that is lowered becomes
the first object in the list.
It looks like a bad idea to mess with this list.
Maybe. But why risk it? Can't you just copy the QObjectList and sort your local copy?
I am using QT4 and dynamically adding entries to a QMenu. Is it possible to sort the entries in the QMenu without deleting it and creating a new one?
I originally thought there was a function to insert at a specific location so I could sort on insert, but I have not been able to locate it.
Once added, I don't think you can reorder. While you are creating though you could use the QWidget::insertAction method to place it exactly where you want it.
void QWidget::insertAction ( QAction * before, QAction * action )
Otherwise you could use QWidget::addActions. Create your list of Actions and sort it before adding to the QMenu.
void QWidget::addActions ( QList<QAction *> actions )
In one of my codes, I save the QActions into a separate List and generate the menus and submenus on demand. In theory, I can add "weight" to the items and have them re-ordered, but I have not implemented this yet.
Project page is available here: http://code.google.com/p/qtedit4/wiki/qmdilib
Please note that the actions of QWidget (and QMenu) are stored as a QList which can be "read", using QWidget::actions() . Remember that the list is copied, so you can modify the actions but not the list itself. (I hope I am not mistaking...)