如何从另一个类读取结构成员

Question

I have a struct in my mainwindow class:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include "dialog.h"
#include <QMainWindow>

namespace Ui {
  class MainWindow;
}

class MainWindow : public QMainWindow
{
  Q_OBJECT

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

    struct properties{
      int ID = -1;
    };

    properties ret_func();
  private slots:
    void on_btn1_clicked();

  private:
    Ui::MainWindow *ui;
    properties _properties;
    Dialog *_dialog;
};

#endif // MAINWINDOW_H

I set value to it's memeber in mainwindow.cpp by clicking on btn1 :

MainWindow::properties MainWindow::ret_func()
{
  return _properties;
}

void MainWindow::on_btn1_clicked()
{
  _properties.ID = ui->lineEdit->text().toInt();
  qDebug()<<_properties.ID;
  _dialog->exec();
}

by clicking on btn1 another window is opened and I want to read the struct member value by clicking on btn2 . This is my code:

void Dialog::on_btn2_clicked()
{
    qDebug()<<MainWindow::ret_func().ID;//->this line has error
}

Error:

error: cannot call member function 'MainWindow::properties 
MainWindow::ret_func()' without object
 qDebug()<<MainWindow::ret_func().ID;
                                ^

I have read some threads having similar problems but couldn't find solution please help me

Answer 1

MainWindow::ret_func() is not a static member, this is why the compiler says error: cannot call member function .. without object

You need to have the instance of MainWindow to apply ret_fun on it.

If you have only one MainWindow you can modify that class to be a singleton to be able to do MainWindow::instance().ret_func().ID;MainWindow::ret_func().ID;