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

Eddy

The link to the QSignalmapper docs I gave you has an example that is similar to what you want. I suggest you start with it and then use the setIcon method later on.

You can ask specific questions as you proceed. If you show us some code of what you accomplished it's easier to help.

goetz

Then please switch to Qt4. You can always get the sources from the "Qt download pages":http://qt.nokia.com/downloads/downloads#qt-lib (get the as tar.gz) and compile Qt yourself, it's only a matter of a

@
./configure
make
sudo make install
@

combo.

Qt3 is outdated and definitely not recommended for new projects - only use it if you absolutely must. Qt5 is in a rise already!

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.