How do you add slots?

[rakkar]

In Visual Studio, I used File / New / QT4 Projects / Qt Application, and now have an application. In QT Designer I want a slot on my class that I can call from a button press. I tried going to the header file for the class (TestApp.h) and adding

public slots:
void MyNewSlot( void );

This compiled, but in QT Designer under Signal / Slot Editor, "MyNewSlot" wasn't added to the dropdown list under Slot(). Only the options that were already there show up (close(), update(), etc)

How do I get new slots to be selectable in the Signal / Slot editor?

Is there documentation on this somewhere? Everything I have seen assumes you are using text files only, and tends to be incomplete.

[franz]

You don't. Designer doesn't parse any cpp or h files.

[rakkar]

How would you ever get a callback in C++ when a button is pressed then?

[victor.fernandez]

Connect the signal to the slot in your code using QObject::connect() (http://qt.nokia.com/doc/4.5/qobject.html#connect-2). For example:

In the header file:


class MyClass : public QWidget, private Ui::MyWidget {
Q_OBJECT

public:
MyClass(QWidget *parent = 0);

public slots:
void mySlot();
}

In the source file:

MyClass::MyClass(QWidget *parent)
: QWidget(parent)
{
setupUi(this);

connect(m_button, SIGNAL(clicked()),
this, SLOT(mySlot()));
}

[Lykurg]

...or let Qt work for you:

slot: on_<object name>_<signalname>(), where you have to substitute <object name> and <signalname>.

[wysota]

... or add the slot directly in Designer.

[Archimedes]

How would you ever get a callback in C++ when a button is pressed then?

Keep in mind that the moc tool will generate a class based on what you've done in the designer.
Then you subclass it and add more functionality (slots, even new widgets, etc) in the new class.

[maurelio79]

Ok. I'm starting to use .ui (in this way is faster build a gui), but i'm not able to add an action to a mine button.

MainWindow.h



#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QtGui/QMainWindow>
#include <QtNetwork>

namespace Ui
{
class MainWindow;

}

class MainWindow : public QMainWindow
{
Q_OBJECT

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

private:
Ui::MainWindow *ui;

public slots:
void connectNet();
};


#endif // MAINWINDOW_H



MainWindow.cpp



#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::connectNet()
{
//Some Stuff;
}


In the MainWindow.ui i have a cancel button (no problem with, because i added a close() slot with gui), but if i want to add a myFunction to other button??

I tried different thing but usually i get:



/home/maurelio/pgm/qt-sdk/esercizi/FirstGui/mainwindow.h:21: error: ISO C++ forbids declaration of ‘connectAction’ with no type


Or i get


/home/maurelio/pgm/qt-sdk/esercizi/FirstGui/mainwindow.cpp:9: error: ‘connectButton’ was not declared in this scope


but connectButton is in the ui file.

[victor.fernandez]

In the MainWindow.ui i have a cancel button (no problem with, because i added a close() slot with gui), but if i want to add a myFunction to other button??

You would need to subclass the button in order to add a method. However, you normally don't need to, since you can just add myFunction to MainWindow and connect the clicked() signal to your slot.


/home/maurelio/pgm/qt-sdk/esercizi/FirstGui/mainwindow.h:21: error: ISO C++ forbids declaration of ‘connectAction’ with no type

This error usually happens when you forget to add an #include for the class. However, I don't think connectAction is a class but I guess it's an object, so you probably forgot to specify the class name. e.g.:


...
public slots:
void connectNet();

private:
QAction *connectAction;
...


/home/maurelio/pgm/qt-sdk/esercizi/FirstGui/mainwindow.cpp:9: error: ‘connectButton’ was not declared in this scope

This means there's no such connectButton in MainWindow. If you added it in Qt Designer, you would have to use ui->connectButton instead. You could make MainWindow a subclass of Ui::MainWindow. This way you could directly access connectButton without needing to add "ui->".


#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QtNetwork>
#include "ui_mainwindow.h"

class MainWindow : public QMainWindow, private Ui::MainWindow
{
Q_OBJECT

public:
MainWindow(QWidget *parent = 0);

public slots:
void connectNet();
};

#endif // MAINWINDOW_H


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

MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
setupUi(this);

connect(connectButton, SIGNAL(clicked()), this, SLOT(connectNet()));
}

void MainWindow::connectNet()
{
//Some Stuff;
}

[maurelio79]

Yes, you're right, i forgot to declare QAction.... sorry, but i'm try to learn both: C++ and Qt, no much time and for me is very difficult. Thanks very much.

Maybe i'm wrong, but it seems that using ui file, the application is a little bit slow, without ui file (using code to make gui) on my FreeRunner the application is faster.

Is it possible in your opinion?

[wysota]

sorry, but i'm try to learn both: C++ and Qt, no much time and for me is very difficult.
Save yourself pain and learn C++ first before taking on Qt.


Maybe i'm wrong, but it seems that using ui file, the application is a little bit slow, without ui file (using code to make gui) on my FreeRunner the application is faster.

Is it possible in your opinion?

No, it's not possible.