Best way to access members in MainWindow from a child class?

[dmginc]

In my MainWindow class, I'm creating a class and passing QLabels like so:

new_class = new NewClass(QLabel1, QLabel2);

new_class = new NewClass(QLabel1, QLabel2);

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NewClass constructor:

NewClass::NewClass(QLabel *qLabel1, QLabel *qLabel2) : qLabel1(qLabel1), qLabel2(qLabel2)
{
}

NewClass::NewClass(QLabel *qLabel1, QLabel *qLabel2) : qLabel1(qLabel1), qLabel2(qLabel2)
{
}

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NewClass definition

class NewClass : public QObject
{
    Q_OBJECT
 
public:
    NewClass(QLabel *qLabel1, QLabel *qLabel2);
private:
    QLabel *qLabel1;
    QLabel *qLabel2;
}

class NewClass : public QObject
{
    Q_OBJECT

public:
    NewClass(QLabel *qLabel1, QLabel *qLabel2);
private:
    QLabel *qLabel1;
    QLabel *qLabel2;
}

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The above method works fine and I am able to access and directly modify the QLabels in the main window from new_class. However, I am wondering if there is a better way to do this?

I believe this method will get quite tedious when I may need to access and modify many more objects contained in the MainWindow (as I will have to pass every single widget!).

Can I just pass a reference to the entire MainWindow?

Any help or insight would be kindly appreciated

[stampede]

Assuming that you only want to update label's text, maybe better approach could be not passing any single widget pointer at all ?
MainWindow owns the labels, so better design IMHO would be to define a class / struct for data modified in NewClass:

typedef struct{
QString labelText1;
QString labelText2;
QWhatever otherData;
} data_to_pass;

typedef struct{
QString labelText1;
QString labelText2;
QWhatever otherData;
} data_to_pass;

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Then define slot in MainWindow:

void MainWindow::updateData(const data_to_pass& newData);

void MainWindow::updateData(const data_to_pass& newData);

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and signal in NewClass:

signals:
void sendNewData(const data_to_pass& newData);

signals:
void sendNewData(const data_to_pass& newData);

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Then you could add new data just by modifying the struct and MainWindow's updateData slot implementation.

You can just modify the struct slightly to get control over more label's parameters ( size, position, text color ect. )

[wysota]

I'd say that you should never need to pass pointers to widgets to some other widgets. Either use signals and slots directly or delegate the access to the widget to a class that owns the widget. In your case MainWindow should be the only class accessing the labels directly.

[dmginc]

Assuming that you only want to update label's text, maybe better approach could be not passing any single widget pointer at all ?
MainWindow owns the labels, so better design IMHO would be to define a class / struct for data modified in NewClass:

typedef struct{
QString labelText1;
QString labelText2;
QWhatever otherData;
} data_to_pass;

typedef struct{
QString labelText1;
QString labelText2;
QWhatever otherData;
} data_to_pass;

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Then define slot in MainWindow:

void MainWindow::updateData(const data_to_pass& newData);

void MainWindow::updateData(const data_to_pass& newData);

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and signal in NewClass:

signals:
void sendNewData(const data_to_pass& newData);

signals:
void sendNewData(const data_to_pass& newData);

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Then you could add new data just by modifying the struct and MainWindow's updateData slot implementation.

You can just modify the struct slightly to get control over more label's parameters ( size, position, text color ect. )

That's a nice idea.
However, I am actually using setPixmap() to show frames in the QLabel

i.e.

qLabel1->setPixmap(QPixmap::fromImage(frame));

qLabel1->setPixmap(QPixmap::fromImage(frame));

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So I would like to work DIRECTLY with qLabel1 within new_class.

@wysota: So passing a reference to QLabel to new_class isn't a good idea?

[wysota]

@wysota: So passing a reference to QLabel to new_class isn't a good idea?

No, it isn't. If you want to show frames of an animation then either use QMovie or emit frames with a signal and connect them to a slot in QLabel.