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 ?