QListView & item movement

SGaist

Can you share how you setup your QListView ?

shahriar25

@SGaist
I create a queueModel and set the listView's model to queue model. the Items in queueModel have a few userRole data. this is the slot that connets to doubleClicked signal on a track that I have in my trackModel:

for (int i=0; i<trackModel->rowCount(); ++i)
{
queueModel->setItem(i, trackModel->item(i)->clone());

    const QPixmap *artWork = new QPixmap;
    artWork = ui->trackArtLabel->pixmap();
    queueModel->item(i)->setIcon(QIcon(*artWork));

    QString itemTitle=QString("%1\n%2\n%3")
            .arg(queueModel->item(i)->data(Qt::UserRole+3).toString())
            .arg(queueModel->item(i)->data(Qt::UserRole+4).toString())
            .arg(queueModel->item(i)->data(Qt::UserRole+6).toString());

    queueModel->item(i)->setText(itemTitle);
}

for (int i=0; i<queueModel->rowCount(); ++i)
{
    mediaPlayer.playlist()->addMedia(QMediaContent(QUrl::fromLocalFile(queueModel->item(i)->data(Qt::UserRole+1).toString())));
}

playQueue(item.data(Qt::UserRole+7).toInt());

SGaist

You have a memory leak here. You allocate artWork on the heap and then directly replace its value by the one from trackArtLabel's pixmap. There's no need for that allocation.

Is your queueModel a custom model ?

shahriar25

@SGaist
yes you are right. I'm using QStandardItemModel

shahriar25

Any help would be appreciated.

SGaist

Again, can you show how you initialize your QListView and your model ?

shahriar25

Hi, @SGaist I'm sorry I didn't get the question in the first place
the QListview is initialized from the ui with these

queueView->setObjectName(QStringLiteral("queueView"));
queueView->setEnabled(true);
queueView->setFrameShape(QFrame::NoFrame);
queueView->setFrameShadow(QFrame::Plain);
queueView->setSizeAdjustPolicy(QAbstractScrollArea::AdjustIgnored);
queueView->setEditTriggers(QAbstractItemView::NoEditTriggers);
queueView->setDragEnabled(false);
queueView->setDragDropMode(QAbstractItemView::InternalMove);
queueView->setDefaultDropAction(Qt::TargetMoveAction);
queueView->setAlternatingRowColors(false);
queueView->setSelectionBehavior(QAbstractItemView::SelectItems);
queueView->setIconSize(QSize(150, 150));
queueView->setMovement(QListView::Snap);
queueView->setResizeMode(QListView::Adjust);
queueView->setSpacing(0);
queueView->setViewMode(QListView::ListMode);
queueView->setModelColumn(0);

and the model:

QStandardItemModel *queueModel;

queueModel = new QStandardItemModel(this);

ui->queueView->setModel(queueModel);

asanka424

Ideally you want the dragged item to be placed between existing items, right? You can change standard item flags to disable drops. (ItemIsDropEnabled).

And for getting new index perhaps you can use itemChanged signal?

shahriar25

Hi @asanka424
I tried the Qt::itemIsDropEnabled but the Items in the model get disabled. what should I do?

asanka424

@shahriar25
Hi,
Did you disable drops in QStandardItem or ListView? You have to disable drops in QStandardItem not in the view
setDropEnabled(false)

BTW if you want to implement more custom behaviours I encourage to use QAbstractItemModel where you have more control over these operations.

Thanks

shahriar25

@asanka424
Hi,
I did this in a "for" for every Item:

queueModel->item(i)->setFlags(Qt::ItemIsDropEnabled);

And also I used QStandardModel in my app a lot but if this thing that I want can't be done in QStandardModel I will have to change the model. And also note that QListWidget doesn't have this problem

asanka424

this will enable drops in each item in your model. what you should do is disabling it like this

item->setFlags(item->flags() ^ Qt::ItemIsDropEnabled)

shahriar25

Hi @asanka424 @SGaist
I was able to set the item flags correctly but now I'm having problem with item changed signal.
How do I know where was the Item (it's row) before it was moved? (I can set the item's data to hold the current row but isn't there a better way?)

And also I was searching the QStandardItemModel's signals to find something useful and I found QStandardItemModel::rowsMoved(...) and QStandardItemModel::rowsAboutToBeMoved(...) and I tried them but they don't ge triggred when an item is moved. why is that?

asanka424

You can try dataChanged signal but it won't identify moves explicitly.

BTW does drag and drop work as you expected now?

shahriar25

Hi @asanka424
Yes it does. if it won't work then I will have to set the user data every time an item moves. but I think there has to be another way.

kshegunov

@asanka424

what you should do is disabling it like this

item->setFlags(item->flags() ^ Qt::ItemIsDropEnabled)

Beware of such handling of flags!

It's a very wrong way to do it. If the flag is not set you'll actually enable it, additionally it doesn't work with compound flags! Suppose you have (in binary) a = 010 and b = 110, then a ^ b == 100 which is very different from the expected 000.

The proper way to remove a set of bits is to AND the inversion: a & ~b == 000
/and this can be rigorously proven to be different from a ^ b if you expand the xor in the other basic operations a ^ b = (a & ~b) | (~a & b)/

shahriar25

Hi @kshegunov . Thank you for correcting that I cahnged my code.
I tried the item changed flag and the data of item but it didn't work. I really don't know what to do

kshegunov

@shahriar25
Well I don't know, I can't spot anything plainly wrong, although there isn't much code to begin with. However, this line:

queueView->setDragEnabled(false);

does look suspicious, have you removed it as it had been suggested, because it's not clear from your answer to @asanka424's question.

asanka424

@kshegunov
Yes agree with you. I just replied for the context where I knew the flag is set.

shahriar25

Hi @asanka424 @kshegunov
Sorry for replying late.
an interesting thing happened:
when I set the flags of the items to
queueModel->item(i)->setFlags(queueModel->item(i)->flags() & !Qt::ItemIsDropEnabled);
the items get disabled!
bot when I do:
queueModel->item(i)->setFlags(queueModel->item(i)->flags() ^ Qt::ItemIsDropEnabled);
the is no problem. I think I'm doing something wrong.

ANd I will try:
queueView->setDragEnabled(false);
and get back with a result. thank all of you for answering again. I love this from and the people who answer the questions