How do I access widgets from another class?

[A Former User]

Hello,
since my project has become very complex I'd like to put some functions into different classes (e.g. a .h and .cpp for all functions that manage one specific QListWidget).
I am not totally new to OOP but a little bit lost here.

I have made a new Qt-project and put a pushButton and a label in the UI. Then I created a class called SecondClass and added the secondclass.h and secondclass.cpp to the project.
Now I'd like declare the void on_pushButton_clicked(); function inside the secondclass.h and use it in the secondclass.cpp to edit the label's text.

I have tried several things but always got compilation errors.

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private slots:

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

QObject *uix = Q_NULLPTR;

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    uix = this;
}

MainWindow::~MainWindow()
{
    delete ui;
}

secondclass.h

#ifndef SECONDCLASS_H
#define SECONDCLASS_H
#include <QMainWindow>

class SecondClass
{
public:
    SecondClass();

private slots:
    void on_pushButton_clicked();

private:


};

#endif // SECONDCLASS_H

secondclass.cpp

#include "secondclass.h"


SecondClass::SecondClass()
{

}

void SecondClass::on_pushButton_clicked()
{
    ui->label->setText("text changed"); //error here
}

Any idea?

[mrjj]

Hi
To use signals and slot in a new class it must be a QObject class, meaning it must have that as baseclass
and also contain Q_OBJECT macro.

So to use signals/slots in your class it must be

class SecondClass : public QObject {
Q_OBJECT
...

make sure to clean build folder and do build all after adding it .

---

void SecondClass::on_pushButton_clicked()
{
ui->label->setText("text changed"); //error here
}

Second Class do not have an UI, so what are you trying here ?
do you mean, UI from mainwin ?

For that you should use signal & slots.
like let SecondClass emit signal NewText(text)
and have that hooked up in mainwin to a SLOT
that uses the text.
SecondClass should not directly fiddle with other class UI :)

[A Former User]

Thank you =)
I have cleaned the build and ran qmake.
And yes, by ui->label->setText("text changed"); I meant to access the widget of the mainwindow.ui.

I have updated the class now:

class SecondClass
{
    Q_OBJECT

How do I hook up to the mainwindow now?

[mrjj]

@SnuggleKat

Well you define a new signal.
like

signals:
void MyNewTxt(QString x ) ;

and then in mainwinow

you connect an instance of SecondClass
to some slot in mainwin

like
connect( SECONDCLASSINSTANC, SIGNAL(MyNewTxt(QString), this, SLOT( SOMESLOT IN MAINWIN) );

then in
SecondClass you can
do
emit MyNewTxt("HELLO");

and it will be sent to mainwins slot

[A Former User]

By using

signals:
    void new_text(QString x);

I get the following error: :-1: Fehler: [debug/moc_secondclass.cpp] Error 1

same when I ass Q_OBJECT to the class

[Tirupathi Korla]

@SnuggleKat you have to inherit second class from qobject..
‘’’class SecondClass:public QObject’’’