select multiple items(dragable and non-dragable) causing the non-dragable items to disappear

[CP71]

@Darren Hi
I admit I didn't read the article for absence of time, I'm sorry, but I found this link:

https://stackoverflow.com/questions/43283252/when-dragging-multiple-items-from-qlistwidget-non-draggable-items-get-removed

I hope it help you

[Darren]

@CP71 Thank you Cp71. I read this link previously but do not understand what they mean by creating QMimeData and QDrag objects in your source list widget's mouseMoveEvent.
Secondly, is this a valid bug in QT? why aren't they solve this bug?

[CP71]

@Darren Hi,
Sorry but I don’t understand, don’t worry, depend of my English isn’t good ;), if you didn't fix your problem or if fixed and are requiring further information (but I think you fixed your issue).

The fix is the flag you pass at setDefaultDropAction function, Qt::MoveAction moves the items, Qt::CopyAction copies the items.

I quickly read the article. About the QMineData and QDrag (if I don’t mistake, objects for data transfer via clipboard and drag and drop) mentioned in the article, I did not investigate in depth but I suppose writer says you that Qt manages them and you mustn't delete them.

For me this isn’t a bug of Qt.

Anyway I quickly created a simple example that is based on example in the link, I tried it and works well:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    ui->listWidget->setDragDropMode(QAbstractItemView::DragDrop);
//    ui->listWidget->setDefaultDropAction(Qt::MoveAction);
    ui->listWidget->setDefaultDropAction(Qt::CopyAction);
    ui->listWidget->setSelectionMode(QAbstractItemView::ExtendedSelection);


    ui->listWidget_2->setDragDropMode(QAbstractItemView::DragDrop);
//    ui->listWidget_2->setDefaultDropAction(Qt::MoveAction);
    ui->listWidget_2->setDefaultDropAction(Qt::CopyAction);
    ui->listWidget_2->setSelectionMode(QAbstractItemView::ExtendedSelection);

    fillListWidget(ui->listWidget, 8, "someItem");
    fillListWidget(ui->listWidget_2, 4, "anotherItem");
}

void MainWindow::fillListWidget(QListWidget *listWidget, int numItems, QString txt)
{
    QString newTxt;
    for ( int i=0; i< numItems; i++ )
    {
        QListWidgetItem *item = new QListWidgetItem();
        newTxt = QString("%1_%2").arg(txt).arg(i);

        if ( i % 2 )
        {
            item->setFlags(Qt::ItemIsSelectable | Qt::ItemIsEnabled);
        }
        else
        {
            // If the item is draggable, indicate it with a *
            newTxt += ' *';
            item->setFlags(Qt::ItemIsSelectable | Qt::ItemIsEnabled | Qt::ItemIsDragEnabled );
        }
        item->setText(newTxt);
        listWidget->addItem(item);
    }
}

[Darren]

@CP71 My application needs a MOVE action. Not a COPY action. If you try
ui->listWidget_2->setDefaultDropAction(Qt::MoveAction)
this will cause the non-dragable items to be DELETED.

[CP71]

@Darren Hi
Ok, now I understand your problem.
Sorry.

[Christian Ehrlicher]

Please provide a simple, compilable example so we can take a deeper look on your problem.

[mrjj]

Hi
Using @CP71 (thanks :) code as base it was fast to make sample.
It does seems it does not honor movable if multiple is selected
and after the drop ( which only shows the correct ones) , it seems to delete/remove
all of selection even some were not dropped. ( those without *)

Read to run project
https://www.dropbox.com/s/urt1pwfvqs3xmbj/DragDropFail.zip?dl=0

(tested on win 10, Qt5.12)

[Christian Ehrlicher]

@mrjj : Thx for the reproducer. will take a look on soon.
Since there is no bugreport about this (at least I'm not aware of one) - can someone please create them :)

[Christian Ehrlicher]

Here a first shot: https://codereview.qt-project.org/251888
As a workaround you can override QAbstractItemView::startDrag() and adjust the selected items to only contain the ones which are also dragable.

[mrjj]

Hi
Damn, you are fast :)
Do we still need a bug report ?

[Christian Ehrlicher]

@mrjj It would be nice to have a bug report to get an official bug so it can be better documented later on. I also need to create another testcase for QTreeView and esp. for QListView in icon mode since there is a special handling.

[mrjj]

@Christian-Ehrlicher
https://bugreports.qt.io/browse/QTBUG-73465
Please let me know if i need to change something.