Updating text of a local QLabel as data is altered in C++ - c++

Question

I have the following code, which initializes a label to match an object's id.
for (int i = 0; i < inputVal; ++i)
{
QLabel *newLabel = new QLabel(p0[i]->id, page);
connect(p0, &Npc::setID, [&]
{ newLabel->text() = p0[i]->id; });
layout->addWidget(newLabel);
}
I'm trying to use the above connect to refresh the value of the label any time I change the value of the object's id. However, this doesn't work due to the label going out of scope and its value becoming inaccessible. Is there any way to access the label's value without declaring it outside of this scope?
This also hinges on the slot executing after the signal function does, which I would assume is the case. If it's not, is there any other way to update dynamic labels as object values change?

Answer 1

You can change your code as follows:
for (int i = 0; i < inputVal; ++i)
{
auto *obj = p0[i];
QLabel *newLabel = new QLabel(obj->id, page);
connect(obj, &Npc::setID, [obj, newLabel]
{ newLabel->setText(obj->id); });
layout->addWidget(newLabel);
}
Explanation: even though the pointer newLabel does indeed go out of scope after the loop iteration is finished, the actual QLabel it points to does not - it is created on the heap so it won't be deleted until something deletes it - in your case the layout would take care of it. So you can capture newLabel pointer by value (the address it points to would just be copied into the lambda) as well as the pointer to your object. You'd also need to use proper setText setter method of QLabel to assign new text to it; text method is a getter, it returns a copy of the text stored within the label, not a reference to it.