Qt Mobility Quickstart App

After successfully (though somewhat painfully) building Qt Mobility 1.0 Tech Preview 2, I'm ready to write and run my first Qt Mobility Application.

Okay... technically not my app, but the app from the Qt Mobility Quickstart example.

Building Qt Mobility Quickstart App

1. Make sure to install Qt Mobility and set LD_LIBRARY_PATH environment variable to point to your Qt Mobility install/lib folder.
2. Create a new Qt GUI Project. If you need help here, refer to Hello World Qt GUI App.
3. Paste the following code into main.cpp :
   
   
   

   #include <QApplication>
   #include <QLabel>
   
   #ifdef Q_OS_SYMBIAN
   #include <qsysteminfo.h>
   #else
   #include <QSystemInfo> //(1)
   #endif
   using namespace QtMobility; //(2)
   
   int main(int argc, char *argv[])
   {
       QApplication app(argc, argv);
       QSystemInfo s;
       QLabel *label = new QLabel(QObject::tr("hello ").append(s.currentCountryCode()));
       label->show();
       label->resize(100,30);
       return app.exec();
   }
   

   
   
   
4. Qt Mobility Quickstart tutorial tells you to add this to your project's .pro file:
   
   
   

   CONFIG += mobility
   MOBILITY += systeminfo
   

   
   
   
5. Build the project...
6. At this point I get this error with QNetworkInterface:
   
   
   

   g++ -c -pipe -g -Wall -W -D_REENTRANT -DQT_GUI_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/local/Trolltech/Qt-4.6.0/mkspecs/linux-g++ -I. -I/usr/local/Trolltech/Qt-4.6.0/include/QtCore -I/usr/local/Trolltech/Qt-4.6.0/include/QtGui -I/usr/local/Trolltech/Qt-4.6.0/include -I/usr/local/Trolltech/Qt-4.6.0/include/QtSystemInfo_tp -I/opt/qt-mobility-src-1.0.0-tp2/install/include -I. -o main.o main.cpp
   In file included from /opt/qt-mobility-src-1.0.0-tp2/install/include/QSystemInfo:1,
   from main.cpp:7:
   /opt/qt-mobility-src-1.0.0-tp2/install/include/qsysteminfo.h:50:29: error: QNetworkInterface: No such file or directory
   In file included from /opt/qt-mobility-src-1.0.0-tp2/install/include/QSystemInfo:1,
   from main.cpp:7:
   /opt/qt-mobility-src-1.0.0-tp2/install/include/qsysteminfo.h:183: error: ‘QNetworkInterface’ does not name a type
   make: Leaving directory `/home/ceefour/Sandbox/quickstart-mobility'
   make: *** [main.o] Error 1
   Exited with code 2.
   Error while building project quickstart-mobility
   When executing build step 'Make'
   

   
   
   
7. Seems like Qt Mobility tutorial writer forgot to add dependency to network module that provides QNetworkInterface. Add the following to your .pro file:
   
   
   

   QT       += network

   
   
   
8. Run the project.

Qt Mobility Quickstart in Action

The Quickstart project displays the following very simple dialog:

It looks very simple and harmless, yet it's so powerful.

Why powerful? Because you can build this very same app for all platforms supported by Qt Mobility, and it'll work just as well... that is, displaying the current locale.

Don't believe me? Build and run exactly the same source code on Windows (no changes whatsoever) and voila!

For those who have programmed in Java, this is similar to Java Mobile Edition (J2ME). The primary benefits are:

• It's natively compiled. Therefore, the app runs optimally in all devices and platforms.
• It uses the same underlying library: Qt library and Qt GUI widget toolkit. Unlike Java where you'll use Swing or SWT on the desktop, and Java ME widgets on the client. In all Qt Mobility platforms, you use Qt GUI.
• No need for a Java Runtime Engine (JRE). Most Qt applications are dynamically linked with Qt shared libraries for size and other reasons. You can also statically link Qt libraries for platforms that doesn't have Qt preinstalled. In that regard, Qt app (therefore, Qt Mobility app) is indistinguishable from that platform's native apps.
  

About LD_LIBRARY_PATH

If you don't set LD_LIBRARY_PATH properly, your app still builds successfullly. However, you will encounter the following error when running the app:

/home/ceefour/Sandbox/quickstart-mobility/quickstart-mobility: error while loading shared libraries: libQtSystemInfo_tp.so.1: cannot open shared object file: No such file or directory

Error messages on Windows are slightly different, but same meaning: it cannot find the required binary library files.

c:/qt/2009.05/mingw/bin/../lib/gcc/mingw32/4.4.0/../../../../mingw32/bin/ld.exe: cannot find -lQtSystemInfo_tpd
collect2: ld returned 1 exit status

To resolve this problem, either add the following to $HOME/.bashrc and restart your computer:

# Qt Mobility
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/opt/qt-mobility-src-1.0.0-tp2/install/lib

or, set LD_LIBRARY_PATH from your project settings (not recommended):

1. Switch to Projects mode (Ctrl+4).
2. Choose your project.
3. Under Build Environment, click Show Details.
   
   
   
   
   
   
   
   
4. Select LD_LIBRARY_PATH, click Edit, and append (separated by colon ":") your Qt Mobility path there, e.g. :/opt/qt-mobility-src-1.0.0-tp2/install/lib
   

Run the app now and it should work fine.