Struggle to insert a QListWidgetItem at his old position ...

ademmler

Hi everybody,

I have a QListWidget (Qt 5.15.16 MacOS - C++). I use Drag&Drop to reorder the list items.
I want to put a "moved" item back to its origin position if a certain condition is not matched.
I can Drag&Drop works, programatically "take" the item works also and gets removed.
But inserting the same item back at his origin row fails. Here is sample code:

void MainWindow::slotListWidgetOrderChanged(const QModelIndex &, int from, int, const QModelIndex &, int to)
{	
    qDebug() << "ListWidget order changed from " << from << "to" << to;
    
    if(! mycondition) {
        //Put item back to origin location ...		
        QListWidgetItem* myItem = ui->listWidget->takeItem(from);
        ui->listWidget->insertItem(from, myItem);
        return;
        
    } else {
        
        //Do something else ....
    }
    
}

ChrisW67

@ademmler said in Struggle to insert a QListWidgetItem at his old position ...:

But inserting the same item back at his origin row fails.

What fails about it?

Seems to me, that this moves nothing.

QListWidgetItem* myItem = ui->listWidget->takeItem(from);
ui->listWidget->insertItem(from, myItem);

For example, with from == 1
List widget items: A B C D
Take index 1: myItem = B
List widget items: A C D
Insert at index 1
List widget items: A B C D

SGaist

Hi,

Why not forbid the move if the condition is met ?
That way there's no surprise move of the item.

JonB

@ademmler
As @SGaist says it would be best if you can prevent a move in the first place.
As @ChrisW67 says your code is incorrect. You have omitted to use the to parameter....

ademmler

Thx for your help.

@SGaist: How can I forbid a move, when the item has been moved already.
To explain: item 1,2,3 should not be moved, item 4,5,6,7 ... can be moved.

@ChrisW67: I want to move the taken item back to its old position.
Isn't "from" the old position? Does the position be changed while "dragging" or afterwards?

The aim is: User picks an element, which should not be moved. He drags it to a new position. Now this item should jump back to its old position. and finally the user gets a dialog telling him why this is not possible.

SGaist

Take a look at this part of the model view programming documentation. It describes how to handle drag and drop.

JonB

@ademmler said in Struggle to insert a QListWidgetItem at his old position ...:

@ChrisW67: I want to move the taken item back to its old position.
Isn't "from" the old position? Does the position be changed while "dragging" or afterwards?

I would guess it only changes after the drag/drop. But in any case these two lines

QListWidgetItem* myItem = ui->listWidget->takeItem(from);
ui->listWidget->insertItem(from, myItem);

take an item out at from and immediately put it back in at from so that's just a NOOP.