Qt/Qt Designer (Version 3.x) GUI questions

qt-newbie107

All,

I have made the switch to Qt 4. However, I have scoured over Qt , TrollTech and Nokia pages, examples and web search resources to to attempt finding a Qt4 example tied to my application and I simply cannot find one.

I am in urgent need of a simple example showing the following (hand-code C++ would be OK):

A widget (on top) where a GIF file can be loaded and displayed within it (the GIF files are externally crafted, so that's not a problem)
Two push-buttons (below the widget in 1) ) horizontally placed. Each push-button loads a separate GIF:

push-button 1 loads GIF # 1 in 1)
push-button 2 loads GIF # 2 in 1)

Eddy: You mentioned using QSignalMapper in Qt 4 with setIcon and the smarts on QString to find the right GIF files. I cant' seem to locate it in the examples section of Qt 4. Can you show me a really simple example or send me the code you refer to ?

All: I really need your help.

Thank you very much,

Qt-Newbie

Eddy

this is the "link":http://doc.qt.nokia.com/4.7/qsignalmapper.html#details I gave you. It still works ;)
I know it's not exactly what you want to do but it gives you a good start.

What do you have so far?

loladiro

consider the following:
@
//in mylabel.h
class MyLabel : public QLabel
{
Q_OBJECT

public slots:
void setFileName(QString name)
{
setPixmap(name);
}
};

//in main.cpp
int main(int argc, char *argv[])
{
QApplication app(argc, argv);

 QSignalMapper mapper;
 MyLabel label;
 QPushButton b1;
 QPushButton b2;
 mapper.setMapping(&b1,"gif1.gif");
 mapper.setMapping(&b2,"gif2.gif");
 QObject::connect(&b1,SIGNAL(clicked()),&mapper,SLOT(map()));
 QObject::connect(&b2,SIGNAL(clicked()),&mapper,SLOT(map()));
 QObject::connect(&mapper,SIGNAL(mapped(QString)),&label,SLOT(setFileName(QString)));
 label.show();

 return app.exec&#40;&#41;;

}

@

qt-newbie107

Eddy, Loladiro,

Thanks very much for your replies.

Loladiro: I will start with your code and let you know how I fare.

Qt-Newbie

loladiro

There was a copy&paste error in my code.
I had
@
mapper.setMapping(&b2,"gif2.gif");
@
twice. It's fixed now.

qt-newbie107

Loladiro,

I took your code and made some mods to it so that it would compile without errors using Qt 4.2.1. Here they are:

mylabel.h

@
#ifndef MYLABEL_H
#define MYLABEL_H

#include <QLabel>

//in mylabel.h
class MyLabel : public QLabel
{
Q_OBJECT

public slots:
void setFileName(QString name)
{
setPixmap(name);
}
};

#endif
@

Also, made some mods to main.cpp:

@
#include <QApplication>
#include <QSignalMapper>
#include <QPushButton>

#include "mylabel.h"

//in main.cpp
int main(int argc, char *argv[])
{
QApplication app(argc, argv);

 QSignalMapper mapper;
 MyLabel label;
 QPushButton b1;
 QPushButton b2;
 mapper.setMapping(&b1,"gif1.gif");
 mapper.setMapping(&b2,"gif2.gif");
 QObject::connect(&b1,SIGNAL(clicked()),&mapper,SLOT(map()));
 QObject::connect(&b2,SIGNAL(clicked()),&mapper,SLOT(map()));
 QObject::connect(&mapper,SIGNAL(mapped(QString)),&label,SLOT(setFileName(QString)));
 label.show();

 return app.exec();

}
@

When I run the executable, I get a very small window. When I expand it, I am getting a pure grey background: No pushbuttons. No gifs displayed. Nothing.

Please help.

Thanks,
Qt-Newbie

loladiro

I though you would incorporate it into existing code, my mistake:
@
int main(int argc, char *argv[])
{
QApplication app(argc, argv);

 QWidget mainWidget;

 QSignalMapper mapper;
 MyLabel label;
 QPushButton b1(&mainWidget);
 QPushButton b2(&mainWidget);
 mapper.setMapping(&b2,"gif2.gif");
 mapper.setMapping(&b2,"gif2.gif");
 QObject::connect(&b1,SIGNAL(clicked()),&mapper,SLOT(map()));
 QObject::connect(&b2,SIGNAL(clicked()),&mapper,SLOT(map()));
 QObject::connect(&mapper,SIGNAL(mapped(QString)),&label,SLOT(setFileName(QString)));

 QVBoxLayout verticalLayout(&mainWidget);
 verticalLayout.addWidget(&label);
 QHBoxLayout horizontalLayout(&mainWidget);
 horizontalLayout.addWidget(&b1);
 horizontalLayout.addWidget(&b2);
 verticalLayout.addLayout(&horizontalLayout);

 mainWidget.show();

 return app.exec();

}
@

mlong

You're never calling show() on your buttons.

While, ideally, all the widgets should be children of another parent widget with a layout, etc., the code you have is sufficient to test out the mechanics of the QSignalMapper, but you currently need to show each widget.

Edit: Nevermind. You figured it out. :-)

loladiro

@
Edit: Nevermind. You figured it out. :-)
@
I would have included all that for the beginning, but I thought he wanted an example usage, not a complete app.

mlong

No worries. It all seems to have sorted itself out :-)

qt-newbie107

All,

The example worked ! Thank you all for your notes.

I have further questions:

The worked out example indicates the ability to do the sequence:
Push a Button --> signal/slot --> map a GIFn file --> display GIFn in mylabel

What I would need to do is:

a) Push a Button --> Query an interface --> Receive reply from interface --> signal/slot/map a GIF file based on interface reply --> display GIF in mylabel

Where would I put the stub code to accomplish this ? Is there a Qt 4 solution ?

b) Can I make system call functions in Qt 4 ? I am talking a "system()" type call to a Python 2.4 script I have already developed.

Please reply.

Thank you all,

Qt-Newbie

loladiro

[quote]
Push a Button —> Query an interface —> Receive reply from interface —> signal/slot/map a GIF file based on interface reply —> display GIF in mylabel

Where would I put the stub code to accomplish this ? Is there a Qt 4 solution ?
[/quote]
A little bit trickier, but like:
@

class MyMainWindow
{
QLabel *label;

public slots:
void buttonClicked(int nr)
{
label->setPixmap(queryInterface(nr));
}
};

//and the button creation like:
for(int i = 0; i < maxButtons; ++i)
{
QPushButton *b = new QPushButton(this);
mapper.setMapping(b,i);
connect(b,SIGNAL(clicked()),&mapper,SLOT(map()));
myLayout->addWidget(b);
}

@

Depending on how long it takes to query the interface, you might want to have a separate, slot to set the image that is being called once the interface is done.

[quote]
b) Can I make system call functions in Qt 4 ? I am talking a “system()” type call to a Python 2.4 script I have already developed.
[/quote]

Have a look at "QProcess":http://doc.qt.nokia.com/latest/qprocess.html

DISCLAIMER: The code shown is a use case example and neither complete nor intended for direct use in an application.

qt-newbie107

All,

How do I place text inside the pushbuttons ? I do not see any methods with the QPushButton class. Is it inherited ?

Please reply.

Thanks,
Qt-Newbie

loladiro

Yes, from "QAbstractButton":http://doc.qt.nokia.com/latest/qabstractbutton.html

qt-newbie107

Loladiro,

Thanks. I got the button text labels via the QAbstractButton class.

Please explain where "queryInterface(nr)" is defined. I am a bit confused. Do I need to write a class/method for this ? Is it a wrapper ?

Thanks,
Qt-Newbie

mlong

Qt-newbie, please start a new thread for new topics.

Eddy

I splitted it and used this title :
Can you please recommend a textbook on Qt4

loladiro

[quote author="qt-newbie" date="1313106592"]Loladiro,

Thanks. I got the button text labels via the QAbstractButton class.

Please explain where "queryInterface(nr)" is defined. I am a bit confused. Do I need to write a class/method for this ? Is it a wrapper ?

Thanks,
Qt-Newbie[/quote]

Since I have no idea what kind of interface you have I just put it there to indicate where you have to query your interface.