How to access QMainWindow from another class - c++

Question

// mainwindow.h
#include "ui_MainWindow.h"
#include "parseTextFile.h"
class MainWindow:public QMainWindow
{
Q_OBJECT
public:
MainWindow(void);
private:
Ui_mainWindow ui;
parseFile *fileParse;
public slots:
int onOkButtonClick();
};
// mainwindow.cpp
MainWindow::MainWindow(void)
{
ui.setupUi(this);
connect(ui.OkButton,SIGNAL(clicked()),this,SLOT(onOkButtonClick()));
}
int MainWindow::onOkButtonClick()
{
fileParse = new parseFile(this);
fileParse->parseTextFile();
return 0;
}
int main(int argc,char* argv[])
{
QApplication app(argc,argv);
MainWindow *mainWindow = new MainWindow();
mainWindow->show();
return app.exec();
}
// parseTextFile.h
class parseFile
{
public:
parseFile(QWidget *parent =0);
~parseFile();
int parseTextFile( );
};
// parseTextFile.cpp
#include "parseTextFile.h"
#include <QMessageBox>
parseFile::parseFile(QWidget *parent)
{
}
parseFile::~parseFile()
{
}
int parseFile::parseTextFile( )
{
QMessageBox::information(this,"a","b");
return 0;
}
I can able to access parseTextFile method but i am getting error in QMessageBox. Is it the right way?
How to print QMessageBox in parseTextFile class?
anything needs to add in parseTextFile constructor?

Answer 1

Pass this to QMessageBox::information as a parent is not a valid argument because parseFile is not a QWidget derived class.
For simple, just pass nullptr instead of this :
QMessageBox::information(nullptr ,"a","b");
In this case, the message box belongs to no one. It's will be closed by the user or when the application exits.
PS: you should release the memory after using fileParse to avoid memory leaks.
There are several ways to like with the main window (static pointer, singleton, top widgets enumeration,etc.) but the simplest one, that I thinks you intend to do, is to make parseFile class as QObject derived class and QMainWindow its parent.
class parseFile: public QObject
{
Q_OBJECT
public:
parseFile(QWidget *parent =0);
~parseFile();
int parseTextFile();
};
parseFile::parseFile(QWidget *parent)
:QObject(parent)
{
}
int parseFile::parseTextFile()
{
QWidget * parentWidget = qobject_cast<QWidget *>( parent() ); //<-- QMainWindow instance
QMessageBox::information( parentWidget, "a", "b");
return 0;
}
int MainWindow::onOkButtonClick()
{
fileParse = new parseFile(this);
fileParse->parseTextFile( );
//fileParse should be released by:
//fileParse->deleteLater();
return 0;
}