QPushButton and connect problem(((

[make]

hi! I am new to qt and now I have a little problem((

int main(int argc, char *argv[])
{
  QApplication app(argc, argv);
 
  QWidget wnd;
  wnd.resize(200, 100);
  wnd.setWindowTitle("w3.cpp");
  wnd.show();
 
  QPushButton *btn = new QPushButton("Press Me", &wnd);
  QObject::connect(btn, SIGNAL(clicked()), btn, SLOT(setText("hi!")));
  btn->move(50, 40);
  btn->show();
 
  return app.exec();
}

int main(int argc, char *argv[])
{
  QApplication app(argc, argv);
  
  QWidget wnd;
  wnd.resize(200, 100);
  wnd.setWindowTitle("w3.cpp");
  wnd.show();
  
  QPushButton *btn = new QPushButton("Press Me", &wnd);
  QObject::connect(btn, SIGNAL(clicked()), btn, SLOT(setText("hi!")));
  btn->move(50, 40);
  btn->show();

  return app.exec();
}

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i just want to do such thing - after clicking button its text changes to "hi"))
where is my mistake??? help please((

[Lesiok]

Signal void my_signal() must be connected to slot void my_slot(). Read about QSignalMapper

[wysota]

http://www.qtcentre.org/faq.php?faq=...ot_with_values

[Zlatomir]

There are a lot of issues there:
1) the signature of signal must match with the one of the slot (or the slot must be available to be called with the arguments of the signal - in case the slot has default values for arguments)
2) on the connect statement you don't pass variable names, you don't pass variable values - you can write there only type names

What you want it can be done by inheriting your own button from QPushButton and write it a slot SetDefaultText and code the string parameter to have a default value.

You can read more about signals and slots here

[make]

i've rewritten my code a bit but it still does not work((

//w3.cpp
#include <mybutton.h>
#include <QObject>
 
int main(int argc, char *argv[])
{
  QApplication app(argc, argv);
 
  mybutton *btn = new mybutton("Press me)))");
  QObject::connect(btn, SIGNAL(clicked()), btn, SLOT(setTxt("hi!")));
  btn->show();
 
  return app.exec();
}

//w3.cpp
#include <mybutton.h>
#include <QObject>

int main(int argc, char *argv[])
{
  QApplication app(argc, argv);
  
  mybutton *btn = new mybutton("Press me)))");
  QObject::connect(btn, SIGNAL(clicked()), btn, SLOT(setTxt("hi!")));
  btn->show();

  return app.exec();
}

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//mybutton.h
#include <QtGui>
#include <QString>
 
class mybutton : public QPushButton
{
  public:
    mybutton();
    mybutton(QString txt);
 
  public slots:
    void setTxt(QString txt);
};

//mybutton.h
#include <QtGui>
#include <QString>

class mybutton : public QPushButton
{
  public:
    mybutton();
    mybutton(QString txt);
    
  public slots:
    void setTxt(QString txt);
};

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//mybutton.cpp
#include <mybutton.h>
 
mybutton::mybutton()
{
}
 
mybutton::mybutton(QString txt)
{
  setText(txt);
}
 
void mybutton::setTxt(QString txt)
{
  setText(txt);
  emit clicked();
}

//mybutton.cpp
#include <mybutton.h>

mybutton::mybutton()
{
}

mybutton::mybutton(QString txt)
{
  setText(txt);
}

void mybutton::setTxt(QString txt)
{
  setText(txt);
  emit clicked();
}

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what should i do??

[wysota]

Follow the link I gave you. Pay attention to how your signal/slot connection looks like.

[make]

Can someone tell me what should i do with signals and slots to make my app working??? because i just do not know what to to((( please....

[Zlatomir]

In your class declaration you forgot some things:
1) the Q_OBJECT macro (you need that for signals and slots to work)
2) you didn't put a default parameter for the slot. (slot declaration should be something like: public slots: void setTxt(QString txt = "Hi!"); ) and connect doesn't have anything else but type - no variable name, no value

//don't forget to Rebuild after you add the Q_OBJECT macro (maybe clean all then run qmake and rebuild)

And also you might want to take a QWidget* as a parent and pass it to the QPushButton constructor (so that you won't have memory leaks in your class)

[make]

i have finally done that/ but it still does not work((( maybe there are new mistakes??

//mybtn.h
#ifndef MYBTN_H
#define MYBTN_H
 
#include <QtGui>
#include <QString>
 
class mybtn : public QPushButton
{
  Q_OBJECT
 
  public:
    mybtn(QString txt);
 
  public slots:
    void setTxt(QString txt = "hi!");
};
 
#endif

//mybtn.h
#ifndef MYBTN_H
#define MYBTN_H

#include <QtGui>
#include <QString>

class mybtn : public QPushButton
{
  Q_OBJECT
  
  public:
    mybtn(QString txt);
    
  public slots:
    void setTxt(QString txt = "hi!");
};

#endif

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//mybtn.cpp
#include <mybtn.h>
 
mybtn::mybtn(QString txt)
{
  setText(txt);
}
 
void mybtn::setTxt(QString txt)
{
  setText(txt);
  emit clicked();
}

//mybtn.cpp
#include <mybtn.h>

mybtn::mybtn(QString txt)
{
  setText(txt);
}

void mybtn::setTxt(QString txt)
{
  setText(txt);
  emit clicked();
}

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//w3.cpp
#include <mybtn.h>
#include <QApplication>
#include <QObject>
 
int main(int argc, char **argv)
{
  QApplication app(argc, argv);
 
  mybtn *btn = new mybtn("Press me))");
  QObject::connect(btn, SIGNAL(clicked()), btn, SLOT(setTxt(QString)));
  btn->show();
 
  return app.exec();
}

//w3.cpp
#include <mybtn.h>
#include <QApplication>
#include <QObject>

int main(int argc, char **argv)
{
  QApplication app(argc, argv);
  
  mybtn *btn = new mybtn("Press me))");
  QObject::connect(btn, SIGNAL(clicked()), btn, SLOT(setTxt(QString)));
  btn->show();
  
  return app.exec();
}

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the application compiles successfully but the button does not change its text((

[Lesiok]

Did You read my previous post ? I think : NO.
This is a warning from Qt when Yout try make connection :

QObject::connect: Incompatible sender/receiver arguments
mybtn::clicked() --> mybtn::setTxt(QString)

[make]

so what should i do with signal clicked()?? i just do not understand((

[wysota]

Look, here is your connect statement:

QObject::connect(btn, SIGNAL(clicked()), btn, SLOT(setTxt(QString)));

QObject::connect(btn, SIGNAL(clicked()), btn, SLOT(setTxt(QString)));

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It says -- whenever btn emits signal clicked(), call method setTxt() on btn, passing it a QString argument. Now the basic question is, what argument (value) should Qt pass to the setTxt() call in this particular situation? Do you think your statement makes sense? Why? If not, what needs to be changed for it to make sense?

[make]

but i thought that:

2) on the connect statement you don't pass variable names, you don't pass variable values - you can write there only type names

so i have written the default value in class implementation...