Accessing label from function gives error

Imran Hassan

Hi everyone,

I am new to QT. I created an application by a wizard. Its UI backend was created as below.

MainWindow::MainWindow(QWidget *parent)
:QmainWindow(parent)
,ui(new UI::MainWindow) {
}

I placed a label on UI with name lbl. I created a timer and a function called myFunc() to update the time on label (lbl). I want to update the label (lbl) with time on every 1 sec tick of timer. I connected the timer signal with slot (myFunc). In myFunc I want to access the label to update the text with correct time but it gives me error.

I want to know two things, in this auto creation of MainWindow class how can I declare private and public data and member functions and second how can I access this lbl from myFunc().

Help will be appreciated.

jsulm

@Imran-Hassan said in Accessing label from function gives error:

it gives me error

What error?!

"how can I declare private and public data and member functions and second how can I access this lbl from myFunc()" - C++ basics? Is myFunc member of your MainWindow?

You should really post your MainWindow code...

Imran Hassan

Let me paste the full code. In TimerSlot() function it is giving error "Use of undeclared identifier ui"

QTimer *timer; // NEW
void TimerSlot(); // NEW slot
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)

, ui(new Ui::MainWindow)

{
//saveSetting();
loadSettings();
ui->setupUi(this);
// this->layout()->setSizeConstraint(QLayout::SetFixedSize);
const QString time = QDateTime::currentDateTime().toString();
ui->currentDateTime->clear();
ui->currentDateTime->setText(time);
timer = new QTimer(this); // create it
connect(timer, &QTimer::timeout, this, TimerSlot); // connect it
timer->start(1000); // 1 sec timer
}

void TimerSlot()
{

ui->lbl.setText(QDateTime::currentDateTime().toString());
}

jsulm

@Imran-Hassan said in Accessing label from function gives error:

void TimerSlot()

Shouldn't it be

void MainWindow::TimerSlot()

?

JonB

@Imran-Hassan

void TimerSlot()

This is simply a global function. You need it to be a member of MainWindow, at least if you expect it to access ui.

Imran Hassan

@jsulm and @JonB Yes it should be but in this auto-created code, I am not able to know how to declare public and private member functions and data.

Can you guide me in this particular scenario? I mean using this above code. I can if I create new application and declare my own class of MainWindow but I have already done a lot of work to create GUI so I want to fix in this code.

Secondly this QT is now allowing me to reply within 10 minutes without earning a reputation.

JonB

@Imran-Hassan said in Accessing label from function gives error:

Yes it should be but in this auto-created code, I am not able to know how to declare public and private member functions and data.

The auto-generated code goes into a file named ui_mainwindow.h in your debug/release directory. This is not a file you see or edit in Creator, and you should not edit this file. You have your own mainwindow.cpp/.h which #includes that file. There you declare your own MainWindow class which inherits from Ui::MainWindow. This file is generated initially by Creator, but thereafter is not altered. You can & should make your own changes in your own mainwindow.cpp/.h files.

Imran Hassan

@Imran-Hassan I got the answer .... To help other here is the answer

can do that in the mainwindow.h file.

class MainWindow {
//...
private slots:
void TimerSlot();
};

Imran Hassan

@JonB Thanks a lot dear.. For such nice help. Can you upvote this question so that I can gain reputation to ask questions frequently

Anyway thanks again for such nice help