Qt - mainwindow class object in another class doesn't work well

void MyAnotherClass::mySlot(){
MainWindow window;
window.myFunction();}

void MainWindow::myFunction(){

qDebug() << "THIS qDebug works well but ui do NOT";

ui->textEdit->setText("Why i do not working?");
}

Why qDebug in this situation works fine, but ui->... doesn't? How to fix it?

EDIT: Solution: `QPlainTextEdit *pointer; MainWindow constructor{ pointer=ui->qPlainTextEdit;}

Some Another's class method{ pointer->appendPlainText("It works"); }`

You create new instance of MainWindow class inside MyAnotherClass::mySlot(). When this slots ends this instance is deleted. So you can't see any changes.

void MyAnotherClass::mySlot() {
    MainWindow window;  //new instance created
    window.myFunction();
} //here this instance deleted

Instead of this you should have pointer to your main window somewhere inside your MyAnotherClass:

MyAnotherClass
{
     .......   
    private slots:
        void mySlot();

    private:
        MainWindow* _mainWindow;
      ...............
};

and then you can do somethins like this:

void MyAnotherClass::mySlot() {
    _mainWindow->myFunction();
}

Of course you should somehow init this pointer before you can use it.