How to call an object created in another function.

[ronyNS]

Hello

I want to call an object of class QLabel in another function . I know this is basic C++ ,but its confusing in Qt .

in my mainwindow.cpp i have created a function

void createlbl(){

QLabel *lbl1 = new QLabel("Hello");

}

void Mainwindow :: resizeEvent(QResizeEvent *evt){


}

i need to call the label object (lbl1) in the resizeEvent function to resize it.
I also need to call the object in other functions in my program.
I tried different ways but i am not getting the right way to call it and use in different functions.
Please tell me what parameters should i pass and how i should call the class or the function in which the class is created to use in different functions.

Thank you

[mrjj]

hi
Object in other functions are not accessible to others unless used as parameter.
The trick is to declare the object in the .h file for the class.
so
QLabel *lbl1; shoud live in mainwindow.h in the class. (public)

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
QLabel *lbl1; //<<<< < this is shared in all functions
};

then it all works out for you.

void createlbl(){
lbl1 = new QLabel("Hello");
}

void Mainwindow :: resizeEvent(QResizeEvent *evt){
lbl1 -> xxx
}

[ronyNS]

@mrjj
Thank you so much!

[mrjj]

@ronyNS
super :)
just a note:
you can get label to fit window automatically- if you use layouts.

[ronyNS]

Yes i am aware of that , but this is the problem https://forum.qt.io/topic/69999/how-to-add-a-label-on-a-layout-that-covers-the-entire-window/2
This is the reason i am using resizeEvent.

[mrjj]

@ronyNS
ok :)
Still not sure why layout wont work but resize event will then.
You just want qLabel to cover all mainwindow ?

[ronyNS]

Yes , like i want to cover my login form , but when i drag the label on the ui it resizes according to the layout.
I used size policy , but when i run it , the main window size is fixed and cannot be reduced.
If there is an easy way , please tell me :)

[mrjj]

@ronyNS
ok, sounds like i dont understand the full setup then.
Maybe resize event will just be easier :)

[ronyNS]

Yes , Thank you ! :)

[ronyNS]

Hey now i am getting 'Expected specifier before Qlabel' error . Please help

[mrjj]

@ronyNS said:

Expected

show line where it says it :)

did u include <QLabel>
in mainwindow. h?

if its for the line
QLabel *lbl1;

[ronyNS]

void createlbl(){
lbl1 = new QLabel("Hello");
}

Error is for this line only when i use lbl1 in other functions. Yes i have included Qlabel in .h file

[mrjj]

@ronyNS
well u are not in mainwindow method..

void XXXX::createlbl(){

XXXX should be mainwindow

when there is no NAME:: in front, its NOT a member function. just a plain function.

[ronyNS]

@mrjj
Still the same error

void MainWindow:: createlbl(){
    lbl1 = new Qlabel();
}

'expected type-specifier before QLabel

[mrjj]

but it should work. ?

show mainwindow.h

here is sample that does so
https://www.dropbox.com/s/i0qj2e9mxbggymt/mylabel.zip?dl=0

[ronyNS]

my mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include<QLabel>
#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

protected:
    void resizeEvent(QResizeEvent *evt) override;

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

my mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include<QLabel>

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

void MainWindow:: createlbl(){
    lbl = new Qlabel();
}

void MainWindow :: resizeEvent(QResizeEvent *evt)
{
    MainWindow::setCentralWidget(lbl);
    lbl->setStyleSheet("Background-color:pink");

    QMainWindow::resizeEvent(evt); //call base implementation
}

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

[mrjj]

@ronyNS said:

lbl = new Qlabel();

misspelled ?
its QLabel ?

lbl = new QLabel();
big L ?