Difference between revisions of "Development/Tutorials/First program"

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This [https://develop.kde.org/docs/getting-started/hello_world/ first program] page was move [https://develop.kde.org/docs/getting-started/hello_world/ here].
series=Beginner Tutorial|
name=Hello World|
pre=[http://mindview.net/Books/TICPP/ThinkingInCPP2e.html C++], [http://www.trolltech.com/products/qt/ Qt], [[Getting_Started/Build/KDE4|KDE4 development environment]]|
next=[[Development/Tutorials/Using_KXmlGuiWindow|Tutorial 2 - KXmlGuiWindow]]|
Your first program shall greet the world with a friendly "Hello World", what else? For that, we will use a {{class|KMessageBox}} and customise one of the buttons.
{{tip|To get more information about any class you come across, Konqueror offers a quick shortcut. So to look for information about KMessageBox, just type "kde:kmessagebox" into Konqueror and you'll be taken to the documentation.}}
You might want to use KDevelop for your projects, which does many nice things like code completition, easy access to API documentation or debugging support.
Read [[Getting_Started/Set_up_KDE_4_for_development#KDevelop|this tutorial]] to set up KDevelop correctly for this task. You probably want to check if the setup is working by testing opening an existing KDE 4 application with KDevelop first.
You still need to edit the CMake files by hand though.
==The Code==
All the code we need will be in one file, <tt>main.cpp</tt>. Create that file with the code below:
<code cppqt>
#include <QString>
#include <KApplication>
#include <KAboutData>
#include <KMessageBox>
#include <KCmdLineArgs>
int main (int argc, char *argv[])
  KAboutData aboutData( "tutorial1", "Tutorial 1",
                        "1.0", "KMessageBox popup",
                        KAboutData::License_GPL, "(c) 2006" );
  KCmdLineArgs::init( argc, argv, &aboutData );
  KApplication app;
  KGuiItem guiItem( QString( "Hello" ), QString(),
                    QString( "this is a tooltip" ),
                    QString( "this is a whatsthis" ) );
  KMessageBox::questionYesNo( 0, "Hello World",
                              "Hello", guiItem );
The first KDE specific code we come across in this program is {{class|KAboutData}}. This is the class used to store information about the program such as a short description, authors or license information. Pretty much every KDE application should use this class.
Then we come to {{class|KCmdLineArgs}}. This is the class one would use to specify command line switches to, for example, open the program with a specific file. However, in this tutorial, we simply initialise it with the {{class|KAboutData}} object we created so we can use the <tt>--version</tt> or <tt>--author</tt> switches.
On line 13 we create a {{class|KApplication}} object. This needs to be done exactly once in each program since it is needed for things such as [[Development/Tutorials/Localization/i18n|i18n]].
Now we've done all the necessary KDE setup, we can move on to doing interesting things with our application. We're going to create a popup box but we're going to customise one of the buttons. To do this customisation, we need to use a {{class|KGuiItem}} object. The first argument in the {{class|KGuiItem}} constructor is the text that will appear on the item (in our case, a button). Then we have an option of setting an icon for the button but we don't want one so we just give it <tt>QString()</tt>. Finally we set the tooltip (what appears when you hover over an item) and finally the "What's This?" (accessed through right-clicking or Shift-F1) text.
Now we have our item, we can create our popup. we call the <tt>KMessageBox::questionYesNo()</tt> function which, by default, creates a message box with a "Yes" and a "No" button. The second argument is the text that will appear in the middle of the popup box. The third is the caption the window will have and finally we set the KGuiItem for (what would normally be) the "Yes" button to the <tt>KGuiItem guiItem</tt> we created.
We're all done as far as the code is concerned. Now to build it and try it out.
If you set up your environment as described in [[Getting_Started/Build/KDE4|Getting_Started/Build/Unstable_Version]], you can compile this code with
gcc main.cpp -o tutorial1 \
-I/home/kde-devel/qt-copy/include/Qt \
-I/home/kde-devel/qt-copy/include/QtCore \
-I/home/kde-devel/qt-copy/include \
-I/home/kde-devel/kde/include/KDE \
-I/home/kde-devel/kde/include \
-L/home/kde-devel/kde/lib \
-L/home/kde-devel/qt-copy/lib -lQtCore -lQtGui -lkdeui -lkdecore
and then run it with
dbus-launch ./tutorial1
===Using CMake===
If that worked, you may want to use [[Development/Tutorials/CMake|CMake]], just like the rest of KDE. This will automatically locate the libraries and headers for KDE, Qt etc. and will allow you to easily build your applications on other computers.
Create a file named CMakeLists.txt in the same directory as main.cpp with this content:
project (tutorial1)
find_package(KDE4 REQUIRED)
include_directories( ${KDE4_INCLUDES} )
set(tutorial1_SRCS main.cpp)
kde4_add_executable(tutorial1 ${tutorial1_SRCS})
target_link_libraries(tutorial1 ${KDE4_KDEUI_LIBS})
The <tt>find_package()</tt> function locates the package that you ask it for (in this case KDE4) and sets some variables describing the location of the package's headers and libraries. In this case we will use the <tt>KDE4_INCLUDES</tt> variable which contains the path to the KDE4 header files.
In order to allow the compiler to find these files, we pass that variable to the <tt>include_directories()</tt> function which adds the KDE4 headers to the header search path.
Next we create a variable called <tt>tutorial1_SRCS</tt> using the <tt>set()</tt> function. In this case we simply set it to the name of our only source file.
Then we use <tt>kde4_add_executable()</tt> to create an executable called <tt>tutorial1</tt> from the source files listed in our <tt>tutorial1_SRCS</tt> variable. Finally we link our executable to the KDE4 kdeui library using <tt>target_link_libraries()</tt> and the <tt>KDE4_KDEUI_LIBS</tt> variable which was set by the <tt>find_package()</tt> function.
====Make And Run====
Again, if you set up your environment as described in [[Getting_Started/Build/KDE4|Getting_Started/Build/Unstable_Version]], you can compile this code with:
And launch it as:
==Moving On==
Now you can move on to [[Development/Tutorials/Using_KXmlGuiWindow|using KXmlGuiWindow]].

Latest revision as of 14:30, 8 September 2020

This first program page was move here.

This page was last edited on 8 September 2020, at 14:30. Content is available under Creative Commons License SA 4.0 unless otherwise noted.