Drag and Drop in ItemView dependant on Item

gde23

Hello,

I have a QTreeView with a model where I want to be able to drag and drop Items of type A onto Items of type B, and also Items of type C onto items of type D.

I've implemented drag and drop for items of type A to B by returning Qt::ItemIsDragEnabledflags for A and Qt::ItemIsDropEnabled flags for B.

However I do not know how I can switch the Qt::ItemIsDropEnabled flag depending on the item that is currently dragged around? What would be the right way to implement this?

VRonin

You should implement a method to change the Qt::ItemIsDropEnabled flag for an index in the model (e.g MyModel::setFlags(const QModelIndex&,Qt::ItemFlags) basically the same as QStandardItem::setFlags for QStandardItemModel) then do something like this:

class MyView : public QTreeView {
    Q_OBJECT
    Q_DISABLE_COPY(MyView)
public:
    MyView(QWidget *parent = nullptr) 
        : QTreeView (parent)
    {}
protected:
    void dragMoveEvent(QDragMoveEvent *event) override{
        const QModelIndex index = indexAt(event->pos());
        const bool canBeDropped = checkIfItemDraggedCanBeDroppedOnIndex(index); // this depends on your logic
        const Qt::ItemFlags oldFlags = model()->flags(index);
        MyModel* mdl = nullptr;
        if(!canBeDropped && index.isValid() && (oldFlags & Qt::ItemIsDropEnabled)){
            mdl = dynamic_cast<MyModel*>(model());
            Q_ASSERT(mdl);
            mdl->setFlags(index,oldFlags & ~Qt::ItemIsDropEnabled);
        }
        QTreeView::dragMoveEvent(event);
        if(mdl)
            mdl->setFlags(index,oldFlags);
    }
};

gde23

Thanks, that brought me a step further, but I still don't get how I find the item that is currently drag and dropped inside checkIfItemDraggedCanBeDroppedOnIndex(index) because the results depends on the type of that item.

VRonin

index is the model index of the destination item if what you don't know what the source item is then you can access its data as described here

gde23

Yeah, I mean the source item.
Since I didn't want to mess around with the mime data I now ended up with another approach:
In the mimeData() method of my model I set a boolen flag on the item that is currently the one that is dragged around. Now in the flags() method I get the flagged item from the model and look what type it is and depending on that I can decide whether drops are enabled on the underlying item or not. This works fine, however it still looks like a bit of a hack.