Qt5 Tutorial Main Window and Action - 2020

In this tutorial, we will learn how to setup the action from the menu and toolbar of the Main Window class.

File->New File or Project...

Applications->Qt Gui Application->Choose...

We keep the class as MainWindow as given by default.

Hit Next.

Hit Finish.

Here is the main.cpp:

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    
    return a.exec();
}

From the highlight line, we have an incident of the MainWindow class.

Here is the header file: mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
    
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
    
private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

Note that we have a namespace UI, and our MainWindow is under the UI scope. Also, in the header, we declared a pointer to the UI::MainWindow as a private member, ui.

Let's open up Designer by double-clicking the mainwindow.ui to put menu bar and action. Type in "File" at the top menu, and "New Window..." under the "File" menu. We need to press Enter to make a real change in the menu. Notice that at the bottom, in the Action Editor, a new action called actionNew_Window has been created.

We can also drag the actionNew_Window action menu and drop in the toolbar:

Now, we have two places to trigger actionNew_Window action.

Click the action on the Action Editor, and select "Go to Slot...".

It allows us to trigger an event. Select triggered() and hit OK.

Then, Creator will show the changes in the code (mainwindow.cpp) automatically:

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_actionNew_Window_triggered()
{
    
}

So, whenever we click either toolbar item or menu item, this event will be triggered.

If we run the code, we get:

When we click the New Window, nothing happens. This is because we haven't put anything into the MainWindow::on_actionNew_Window_triggered() method.

Right click on MainWindowAction project->Add New->Qt->Qt Designer Form Class->Dialog without Buttons

New files related to our new dialog have been created:

Let's put the proper code for the triggered event.
We'll open up the new dialog in two types: modal and modaless.

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "mydialog.h"
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_actionNew_Window_triggered()
{
    MyDialog mDialog;
    mDialog.setModal(true);
    mDialog.exec();
}

If we run it, we get the modal type dialog:

To get modeless, we editted the mainwindow.cpp as below:

void MainWindow::on_actionNew_Window_triggered()
{
    MyDialog mDialog;
    /*
    mDialog.setModal(false);
    mDialog.exec();
    */
    mDialog.show();
}

But it disappears as soon as it is created. That's because unlike modal type dialog, modaless gives control to the main app, the stack variable goes away when it gets out of on_actionNew_Window_triggered(). So, we need to set a pointer as a member of the MainWindow class:

mainwindow.cpp:

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "mydialog.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_actionNew_Window_triggered()
{
    mDialog = new MyDialog(this);
    mDialog->show();
}

mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

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

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
    
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
    
private slots:
    void on_actionNew_Window_triggered();

private:
    Ui::MainWindow *ui;
    MyDialog *mDialog;
};

#endif // MAINWINDOW_H

Now, modeless dialog does not disappear.

Qt 5 Tutorial

1. Hello World
2. Signals and Slots
3. Q_OBJECT Macro
4. MainWindow and Action
5. MainWindow and ImageViewer using Designer A
6. MainWindow and ImageViewer using Designer B
7. Layouts
8. Layouts without Designer
9. Grid Layouts
10. Splitter
11. QDir
12. QFile (Basic)
13. Resource Files (.qrc)
14. QComboBox
15. QListWidget
16. QTreeWidget
17. QAction and Icon Resources
18. QStatusBar
19. QMessageBox
20. QTimer
21. QList
22. QListIterator
23. QMutableListIterator
24. QLinkedList
25. QMap
26. QHash
27. QStringList
28. QTextStream
29. QMimeType and QMimeDatabase
30. QFile (Serialization I)
31. QFile (Serialization II - Class)
32. Tool Tips in HTML Style and with Resource Images
33. QPainter
34. QBrush and QRect
35. QPainterPath and QPolygon
36. QPen and Cap Style
37. QBrush and QGradient
38. QPainter and Transformations
39. QGraphicsView and QGraphicsScene
40. Customizing Items by inheriting QGraphicsItem
41. QGraphicsView Animation
42. FFmpeg Converter using QProcess
43. QProgress Dialog - Modal and Modeless
44. QVariant and QMetaType
45. QtXML - Writing to a file
46. QtXML - QtXML DOM Reading
47. QThreads - Introduction
48. QThreads - Creating Threads
49. Creating QThreads using QtConcurrent
50. QThreads - Priority
51. QThreads - QMutex
52. QThreads - GuiThread
53. QtConcurrent QProgressDialog with QFutureWatcher
54. QSemaphores - Producer and Consumer
55. QThreads - wait()
56. MVC - ModelView with QListView and QStringListModel
57. MVC - ModelView with QTreeView and QDirModel
58. MVC - ModelView with QTreeView and QFileSystemModel
59. MVC - ModelView with QTableView and QItemDelegate
60. QHttp - Downloading Files
61. QNetworkAccessManager and QNetworkRequest - Downloading Files
62. Qt's Network Download Example - Reconstructed
63. QNetworkAccessManager - Downloading Files with UI and QProgressDialog
64. QUdpSocket
65. QTcpSocket
66. QTcpSocket with Signals and Slots
67. QTcpServer - Client and Server
68. QTcpServer - Loopback Dialog
69. QTcpServer - Client and Server using MultiThreading
70. QTcpServer - Client and Server using QThreadPool
71. Asynchronous QTcpServer - Client and Server using QThreadPool
72. Qt Quick2 QML Animation - A
73. Qt Quick2 QML Animation - B
74. Short note on Ubuntu Install
75. OpenGL with QT5
76. Qt5 Webkit : Web Browser with QtCreator using QWebView Part A
77. Qt5 Webkit : Web Browser with QtCreator using QWebView Part B
78. Video Player with HTML5 QWebView and FFmpeg Converter
79. Qt5 Add-in and Visual Studio 2012
80. Qt5.3 Installation on Ubuntu 14.04
81. Qt5.5 Installation on Ubuntu 14.04
82. Short note on deploying to Windows