Development/Tutorials/KDE3/Qt Designer and KDevelop 3.0 for Beginners

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To get us started doing something useful with Qt Designer, we are going to build a simple program that will show you the power of Qt Designer and KDevelop. I hope that this will help you to create your first "real" KDE application.

KDevelop will help you to build a complete KDE application. The KDE project uses the autoconf and automake tools for KDE 3.x, and KDevelop will provide you with all the necessary files (admin directory, Makefile.cvs,,...).


How to Get Qt Designer

From your Distribution

Qt Designer is part of the qt-3.2.x package and above. If you have an older Qt on your system, you should get at least this version. At the time of writing, Qt latest version is 3.3.2.

Please remember to check if you have all the qt-related packages installed. You need the qt headers in order to compile this tutorial application. These headers usually come in the devel package. You also need to be sure you have designer. In some distributions, it comes in a separate package.

To check if you have everything, do a:

locate qstring.h

If you get something like /usr/lib/qt3/include/qstring.h then you can set your QTDIR variable to /usr/lib/qt3/. In bash environment, this is done by typing:

export QTDIR= /usr/lib/qt3

Tarball or Anonymous Subversion

You can download the tarball from the Trolltech website, or get the qt-copy module from SVN. Please note that Qt for Linux is GPL.

For an explanation for how to use anonymous SVN, get the qt-copy and kde modules and compile them, please see a great documentation at Using Subversion with KDE.

You must then set the QTDIR environment variable. This should point to the directory into which you installed Qt. In bash, for example, you would type:

export QTDIR= /usr/local/qt

provided that /usr/local/qt is the directory into which you installed Qt. Please read the INSTALL file for more details.

You then compile by issuing the following commands, here is the recommended compile line:

./configure -system-zlib -qt-gif -system-libpng -system-libjpeg \ -plugin-imgfmt-mng -thread -no-exceptions -debug -fast make

The command make install is not needed.

Qt Designer is located in the bin directory of your Qt installation directory. You can run it by typing: /usr/local/qt/bin/designer in a console.

To compile Qt from source, please see Trolltech's Qt/X11 Open Source Edition page.

How to get KDevelop 3

From your Distribution

KDevelop 3 should be part of your distribution. Pre 3 versions of KDevelop were nicknamed Gideon, but they are obsolete now.

From Tarball

KDevelop can be downloaded from the KDevelop website, under the Quick download heading.

To compile KDevelop 3, you need qt-3.1.0 or higher and kdelibs-3.1.0 or higher. The environment variables QTDIR and KDEDIR should point to those directories.

Don't forget to set up the KDE and Qt paths. The most common errors while using KDevelop come from the environment variables not set up properly. Check in a console by issuing the command set to see all your environment variables. You should set your PATH variable as follow as well as your LD_LIBRARY_PATH:


If you have any problem getting KDevelop running, please refer to the KDevelop Forum to find the answer to your problem.

If you never used KDevelop before, try to create a new project and to compile it to get used to the interface and the icons.


Please refer to KDevelop - HEAD Download and HEAD Branches SVN Compiling.


  • Widget: a widget is an element of an graphical interface such as a container window, a button or a field for entering text.
  • Layout management: this term describes the way in which widgets are arranged in a window. In its simplest form, an element may be placed at a specific position and given a specific height and width. But when the user resizes the window, the widgets should stay in their position and change their size accordingly. Linux allows to do that by using layouts to place the widgets in.
  • Signal and Slots: Signals and slots are used for communication between objects. The signal/slot mechanism is a central feature of Qt. Signals are emitted by objects when they change their state in a way that may be interesting to the outside world. Slots can be used for receiving signals, but they are normal member functions. You can connect as many signals as you want to a single slot, and a signal can be connected to as many slots as you desire. Please see the TrollTech documentation on signals and slots for more details. In the excellent online documentation that comes with Qt, you'll find the signals and the public slots that go with each class. You can then implement your own slots.

Creating the Application

Starting the project

Creating the framework with KDevelop

The framework in which our program will sit in (i.e. the main window) can be done easily and quickly by using KDevelop. Start KDevelop and select New Project in the Project menu. The Application Wizard appears then. Choose a C++ -> KDE -> Simple KDE Application. Fill in the blank lines with the project name SigCreate, your name as author, and your email. Refer to this screen shot as a reference.

Click on Next. Have a look to the CVS option and the header templates. Then click on Finish on the last screen. KDevelop creates all the files that you need to compile your project. You can use the file selector to view the code of the 3 files which are main.cpp, sigcreate.cpp and sigcreate.h, as shown here.

Once the Application Wizard has created your application, compile it to ensure that everything is fine. To do that, select Build -> Run automake & friends then Build -> Run configure. The Messages output window should say

" Good - your configure finished. Start make now

  • *** Success ***

so you can run make with Build -> Build Project (or using the F8 shortcut). Then Build -> Install. Then Build -> Execute program (or F9). The result is shown here.

  • NOTE - If KDevelop does not recognize your QTDIR and KDEDIR variables, you can set them in Project -> Project Options... in Configure Options, as shown.

Using Qt Designer

Qt Designer is a tool for designing and implementing user interfaces. It helps you arranging your widgets on a form and adding a proper layout so your interface can be resized properly. I recommend that you read the Qt Designer manual to know everything about Qt Designer. Qt Designer includes a code editor but we'll use KDevelop to edit and modify all code.

We will now create the interface of our application using Qt Designer. A form from Qt Designer is saved with a .ui extension because it is then processed by the uic program to generate a .h and .cpp files. KDevelop takes care of that, the only thing we need to do is to create the form.

  • Note - Each time you add or remove a file (now we will add a .ui file) in your KDevelop project, the will be changed. KDevelop does that itself but you will need to Run automake & friends after such changes.

In KDevelop, click on File -> New and fill the dialog window that appears. First write the file name: sigcreatedlg and select what new file you want in the combobox: here we want a Widget (.ui). Please be sure that Add to project is checked, this ensures that the is updated. Refer to this screen shot.

Click the OK button. The Automake manager dialog then pops up. Click the OK button for this dialog as well.

If the new file sigcreatedlg.ui is not open in Qt Designer, open the Automake Manager, right-click on the file and select Open With, then Qt Designer. Qt Designer will open.

  • Note - About the names: it is a good idea to finish a dialog name or a form name by dlg to ensure a nice visibility for people who want to have a look at the code. sigcreatedlg says that it is a dialog, i.e an interface class, only.

The Qt Designer interface is essentially split into three areas. On the left is the toolbox, where you can select your widgets. On the right, several dialogs can be selected. I'll keep only the Property Editor dialog (I close the 2 others). Your widgets can be fine tuned to behave how you want them to. You can choose the size of the widget, its background color (palette), and so on. Between those 2 windows is the Form, your program window, within which you will design your user interface.

  • Note - After adding the sigcreatedlg.ui file, you will have to run Automake & friends and Run configure before building the program. This ensures that the updated is now read.

In Short

Make the translations for a simple kde project

A few general tips

Generating the source (alternate)

Credits and License

Content is available under Creative Commons License SA 4.0 unless otherwise noted.