Defining QString to be used in several classes

gabor53

Hi,
How can I define a QString variable to be able to use it in several classes?
Thank you.

mrjj

Hi
Best design is with signals and slots.

The QString class lives in one class and when changed, the owner class emits the string to the other classes.
They can then keep a copy.

Globals variables are not a good idea.

gabor53

@mrjj
If I assign a value to a variable in the program, is there a signal I can use to send the value to the other class?

DRoscoe

@gabor53 you need to define one

mrjj

@gabor53
No really, you should just define a new signal.
If you use a setter function , you can emit there.
pseudo code:

class MyStrOwner  : QObject {
Q_OBJECT
private:
QString Name; // let just say its name
signals;
void NameChanged( QString );
public;
void setName( QString  NewName) {  
  Name=NewName;
  emit NameChanged(Name);
}
}

Then if u say anywhere

MyStrOwner oneclass;
oneclass.setName("hello");

it will auto emit

gabor53

@mrjj
Thank you!

SGaist

Hi,

Just a fix to @mrjj code. In the setName slot:

void setName( QString  newName) {  
    if (newName == name) {
        return;
    }
  name = newName;
  emit nameChanged(name);
}

Otherwise you can trigger a signal storm if you connect the nameChanged signal to an object that has a connection to the setName slot following the same approach.

Wurgl

@mrjj what about QSharedData or similar from that QShared* classes. Well, the signal might still be needed for detecting a change, but you do not need to copy the data …

mrjj

@Wurgl said in Defining QString to be used in several classes:

QSharedData

You are right. That would be the right way if programmer
want to share and update same data.

I just saw "be able to use it in several classes?" and though
about global variables and how not to do it :)

@SGaist
Thank you. :)