Retrieve parent through a Drag & Drop from a QtreeWidget

mrjj

Hi
If you want better control you will subclass and override (make) the Drop functions and in there you can
get info for the QTreeWidget etc.

https://doc.qt.io/qt-5/dnd.html

I imagine its the QDragMoveEvent you want
so when user drag over some parent, you can read its value.

If first after user drop the item, then the QDropEvent

Can I ask what you need the parent value for ?

coilo

@mrjj said in Retrieve parent through a Drag & Drop from a QtreeWidget:

I imagine its the QDragMoveEvent you want
so when user drag over some parent, you can read its value.
If first after user drop the item, then the QDropEvent
Can I ask what you need the parent value for ?

Sorry if I wasn't clear.
Actually I want to retrieve the parent once my item has been dropped.

(My QtreeWidget is linked with a database, and i need the parent value to complete it because my database does the hierarchization of my tree)

So i should use the QDropEvent right for my case ?

coilo

As suggested i am trying to override the QDropEvent function.

So i wrote in my .h file this :

   void dropEvent(QDropEvent *event) override;

and i saw in the documentation that data are stored in a QMime so i have wrote this code to check if i can have the Parent information

void MainWindow::dropEvent(QDropEvent *event)
{
    const QMimeData *mimeData = event->mimeData();
    qDebug()<<mimeData->text();

}

But there is nothing displayed. I'm stuck :(, do you have any other ideas?
Thanks

mchinand

Did you set the mime data in your QDrag object like in the Drag and Drop example that mrjj linked to above?

coilo

@mchinand Hmmm what do you mean ?
I have set the mime data like this in my function :

void MainWindow::dropEvent(QDropEvent *event)
{
    const QMimeData *mimeData = new QMimeData;
    mimeData = event->mimeData();

    qDebug()<<mimeData->text();
 
}

eyllanesc

@coilo What is your object wanting to get the parent of the dragged QTreeWidget? Maybe there is another solution. I point this out since by default the dnd between QAbstractItemView (like the QTreeWidget) only sends data encoded in a special format and in that data there is no relationship or information to obtain the parent

SGaist

Hi,

@coilo said in Retrieve parent through a Drag & Drop from a QtreeWidget:

As suggested i am trying to override the QDropEvent function.

So i wrote in my .h file this :
   void dropEvent(QDropEvent *event) override;
and i saw in the documentation that data are stored in a QMime so i have wrote this code to check if i can have the Parent information
void MainWindow::dropEvent(QDropEvent *event)
{
    const QMimeData *mimeData = event->mimeData();
    qDebug()<<mimeData->text();

}
But there is nothing displayed. I'm stuck :(, do you have any other ideas?
Thanks

Unless MainWindow is your QTreeWidget it won't get called.

You need to subclass QTreeWidget if you want to alter its DND behavior.

coilo

@eyllanesc Hmmm i see, so there is no way to retrieve the parent's information once the item has been dropped ?

coilo

@SGaist said in Retrieve parent through a Drag & Drop from a QtreeWidget:

Unless MainWindow is your QTreeWidget it won't get called.

Hmmm yes my MainWindow is not my QTreeWidget.
What do you mean by subclassing my QTreeWidget ? What should i change ?

mrjj

@coilo

Hi
Subclassing means make a new class based on the mentioned class

class MyTreeWidget : public QTreeWidget {

public:
    explicit MyTreeWidget(QWidget* parent = nullptr) : QTreeWidget(parent) {}

};

so you want to add the dropXXX functions to that.

and then use MyTreeWidget instead of the plain QTreeWidget

coilo

@mrjj ah okay thank you I understand a bit better.

Hmmmm and what about the dropEvent function what should i change to retrieve the parent information ?

mrjj

Hi
Super. we need to create our own class (subclass) to change the default drop handlers as they are virtual function and
the is the c++ way to implement/change behavior.

Hmmmm and what about the dropEvent function what should i change to retrieve the parent information ?

Well Im not 100% sure that the default MimeData contains both row and col.

The standard mimeformat used can be read like this

https://stackoverflow.com/questions/1723989/how-to-decode-application-x-qabstractitemmodeldatalist-in-qt-for-drag-and-drop

so it might be enough.

If not, you need to handle the DragStart function also to include the information you need.