[SOLVED] Access function in another class



  • Hello, I am trying to access function from another class. I've been googling quite a lot but have not found any useful tips... I know my question concerns C++ more than a Qt, but anyway...

    I have two classes... Class A is reading some data from files and should pass data to class B, and B should write that data to textEdit... How can I call function writeText in class B, from class A? I can not inherit class B or initialize it again, because that would cause mess with db connections in class B... Passing data to class B was successful using static function, but with static I can't access non-static objects, so can't write to textEdit...

    @class A
    {
    void readData();
    }

    void A::readData()
    {
    QString s;
    writeText(s);
    }

    class B
    {
    public:
    void writeText(QString s);
    }

    void B::writeText(QString s)
    {
    ui->textEdit->writePlainHTML(s);
    }@


  • Lifetime Qt Champion

    Hi,

    Since you are modifying a widget, it depends more on how you are triggering the read of class A. What is the use case ?



  • readData in class A is constantly reading file data (every second). When it gets certain data, it should trigger function writeText() from B class...

    For example:
    Reading some text...
    orange
    pineaple
    lemon // When readData reaches that line it should call writeText(lemon)
    apple

    I'd need vice versa "communication" as well... When user click button in class B, it should call getData() in class A...

    @A::QString getData()
    {
    return string;
    }@

    I will have several instances of class A (25-30) and each will process different file...



  • You can work with Signals/Slots of Qt to make it clean separation between Class A and B and still communicate each other.



  • Hi,

    In order to realize this, you have to use a signal/slot mechanism like this :

    @class A
    {

    void readData();

    //add this
    signals:
    writeText( QString );
    }

    void A::readData()
    {
    QString s;
    //writeText(s); replacing this line by :
    emit writeText ( s );
    }@

    and in class B :

    @class B
    {
    A a; // creating an object of A in B

    public slots : // this is a slot, not a ordinary method
    void writeTextB(QString s);

    QObject::connect( &a, SIGNAL (writeText( QString) ), this, SLOT( writeTextB ( QString)) );
    }

    void B::writeTextB(QString s)
    {
    ui->textEdit->writePlainHTML(s);
    }@



  • Could you give me an example?

    EDIT: You already added it, thanks.



  • Ok,

    Try it and give me updated for any further help.



  • It works only one way...

    @
    // This one works... When I emit signal from class B (mainwindow) it trigger function (writeTextA) in class A (character)
    character.h
    class Character : public QObject
    {
    Q_OBJECT
    public:
    Character(QString str);
    ~Character();

    public slots:
    void writeTextA(QString s);
    };

    character.cpp
    void Character::writeTextA(QString s)
    {
    qDebug() << s;
    }

    mainwindow.h
    class MainWindow : public QMainWindow
    {
    Q_OBJECT

    public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

    signals:
    void test(QString s);
    };

    mainwindow.cpp in constructor
    Character ch("test");
    connect(this, SIGNAL(test(QString)), &ch, SLOT(writeTextA(QString)));
    emit test("abce");
    @

    @
    // Does not work... It compile but nothing happens...
    character.h
    class Character : public QObject
    {
    Q_OBJECT
    public:
    Character(QString str);
    ~Character();

    signals:
    void testF(QString s);
    };

    character.cpp in constructor
    emit testF("test");

    mainwindow.h
    class MainWindow;
    }

    class MainWindow : public QMainWindow
    {
    Q_OBJECT

    public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

    public slots:
    void write(QString s);
    };

    mainwindow.cpp in constructor
    Character ch("test");
    connect(&cw, SIGNAL(testF(QString)), this, SLOT(write(QString)));

    void MainWindow::write(QString string)
    {
    qDebug() << string;
    }
    @



  • Added timer to class A and now works... I guess signal in A was emitted before class B initialized connection...

    @QTimer::singleShot(1100, this, SLOT(update()));

    void Character::update()
    {
    emit testF("test");
    }
    @


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