QT拖放-使用qobject_cast创建临时QLabel

Question

I'm trying to give a custom class that inherits from QLabel to be draggable. Towards that end, I'm trying to create a temporary copy of the class at the current mouse position using the following code inside of the class' mousePressEvent:

QLabel *child = qobject_cast{QLabel*}(this->childAt(event->pos()));

NOTE: this line has carrots instead of brackets, but stack overflow interprets it and takes it out if (!child) return;

 NOTE: this line has carrots instead of brackets, but stack overflow interprets it and takes it out if (!child) return; 

The child is never created, and I can't figure out why. Any ideas?

Answer 1

If your code is within your QLabel -derived class, childAt() is not the right function. That would return a child widget contained within your label. It doesn't sound like that is what you are trying to do, but correct me if I am misunderstanding.

The object you want to copy is this , but "copy" can have many meanings in c++, and I am not sure exactly you are trying to do. You will probably have to implement it yourself, perhaps with a method called clone() that creates a new instance of your class and populates the values you need to reproduce.

I suspect, though, that there is a better way to implement the drag and drop functionality you are looking for without a copy.