setPlainText/setText simply won't run

[RandomNobodyEU]

I have made a simple text editor similar to notepad, with some simple functions. I have spent the entire day making a 'load file' dialog, and when everything finally worked, "ui->textEdit->setPlainText();" started failing on me. I think this might actually be a bug, as I can't for the life of me figure out what the problem is.

Anyway, here's the relevant code:

SaveLoad.cpp

QFile myFile(rPath);
#include "mainwindow.h"
 
void SaveLoad::load()
{
    qDebug() << endl << "rPath in SaveLoad.h: " << rPath;
 
    QFile myFile(rPath);
    if (myFile.open(QIODevice::ReadOnly))
    {
        QTextStream textStream(&myFile);
        text = textStream.readAll();
 
        myFile.close();
 
        MainWindow obj;
        obj.setTextFile(text);
    } else{
        qDebug() << "The file didn't open properly";
    }
}

QFile myFile(rPath);
#include "mainwindow.h"

void SaveLoad::load()
{
    qDebug() << endl << "rPath in SaveLoad.h: " << rPath;

    QFile myFile(rPath);
    if (myFile.open(QIODevice::ReadOnly))
    {
        QTextStream textStream(&myFile);
        text = textStream.readAll();

        myFile.close();

        MainWindow obj;
        obj.setTextFile(text);
    } else{
        qDebug() << "The file didn't open properly";
    }
}

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MainWindow.cpp

void MainWindow::setTextFile(QString x)
{
    qDebug() << endl << "This code runs in MainWindow.cpp" << endl << "fullText's content is:" << x << endl;
    ui->textEdit->setText(x);
    qDebug() << "This code(1) runs" << endl;
}

void MainWindow::setTextFile(QString x)
{
    qDebug() << endl << "This code runs in MainWindow.cpp" << endl << "fullText's content is:" << x << endl;
    ui->textEdit->setText(x);
    qDebug() << "This code(1) runs" << endl;
}

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Tell me if that's not enough, then I'll post the entire code or the project file. Anyway, all the qDebugs run as they should. in the qDebug, QString x in void setTextFile(QString x) displays "Hello World!" as it should. The only problems is the line

ui->textEdit->setText(x);

ui->textEdit->setText(x);

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I have tried replacing x with "Hello World!" but that didn't work either so the variable is not the problem. The entire program runs without errors or issues.
The only 'oddity' I noticed was that every variable I stored in SaveLoad.h or any variable in MainWindow.h that I tried to change from SaveLoad.cpp returned to null immediately after running the code.

(If I had, say, QString x in MainWindow.h, and I changed it in SaveLoad.cpp using:

MainWindow object;
object.x = "Hello World!"

MainWindow object;
object.x = "Hello World!"

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then qDebug() << object.x; would return "Hello World!" but if I ran qDebug() << x; in MainWindow then it would return "".

[Lesiok]

How is obj (line 17 in first code) initialised ?

[RandomNobodyEU]

Well I include MainWindow.h in SaveLoad.cpp:
#include "mainwindow.h"

then I create an object:
MainWindow obj;

and then I run the function setTextFile with parameter (text)
obj.setTextFile(text);

I don't think I initialized it anywhere else than in SaveLoad.cpp

Also to add to the OP, nothing in this function runs except for qDebug:

void MainWindow::setTextFile(QString x)
{
    qDebug() << endl << "This code runs in MainWindow.cpp" << endl << "fullText's content is:" << x << endl;
    ui->textEdit->setText(x);
    qDebug() << "This code(1) runs" << endl;
}

void MainWindow::setTextFile(QString x)
{
    qDebug() << endl << "This code runs in MainWindow.cpp" << endl << "fullText's content is:" << x << endl;
    ui->textEdit->setText(x);
    qDebug() << "This code(1) runs" << endl;
}

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I tried setting a global variable equal to x but that didn't work either.

edit: tried

MainWindow *obj = new MainWindow;
obj->setTextFile(text);

MainWindow *obj = new MainWindow;
obj->setTextFile(text);

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but this had the same issue

[wysota]

What is the type of ui->textEdit?

[Lesiok]

OK, You create MainWindow object obj in line 16 (first source), in next line You put text on obj and then obj is destroyed because it is on stack.

[RandomNobodyEU]

Thank you very much everyone! After 24 hours I somehow fixed it!

I still don't know what was wrong with my initial code but I did a workaround.