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Qt4 development

Revision as of 13:17, 8 April 2010

IMPORTANT: This page is for Fremantle PR 1.2 using Qt 4.6. If you want to develop for Diablo or use Qt 4.5 please have a look at the Qt4 Hildon Legacy Page.

File:Intro.png Introduction

To develop with Qt for Maemo, a working SDK installation is required. There are instructions on how to install the Maemo SDK, and you can watch the Maemo SDK in action. Alternatively, you may want to try MADDE, a cross-platform Maemo development tool, available as a technology preview.

File:Rocket.png Getting started

To start to develop with Maemo Qt, we need to install the Maemo SDK.

Since PR 1.2 release Qt 4.6 is available in public Fremantle repository To upgrade older scratchbox targets to use the latest packages execute the following commands:

fakeroot apt-get update
fakeroot apt-get dist-upgrade

You can install Qt with the command:

fakeroot apt-get install libqt4-dev

How to compile a Qt application in scratchbox

Qt applications are usually built using QMake. Project like KDE instead replaced QMake with CMake for more flexibility.

QMake

QMake is a tool from Trolltech that helps simplify the build process for development project across different platforms

You can build your Maemo Qt application in 3 simple steps:

1. Generating project file (Required if there is no .pro file into the app source tree)
   

   qmake -project

2. Generating Makefile from the QMake project file:
   

   qmake file.pro

3. make

CMake

CMake projects usually have a CMakeLists.txt file instead of:

1. .pro file used by QMake projects
2. Makefile.am used by Autotools projects (standard in Unix/Linux)

Using CMake to build the project is extremely easy. In the directory containing CMakeLists.txt, supply the following two commands, where path is the path to the source code.

cmake path
make

Note: CMake is not installed by default in scratchbox. You can install it with the command:

fakeroot apt-get install cmake

Running a Qt application in:

Scratchbox

Diablo and Fremantle Qt applications can run into the device as into scratchbox.

First step to run a Qt application is starting the SDK UI:

1. Run Xephyr. It is able to run a X Server inside another X Server.
   

   Xephyr :2 -host-cursor -screen 800x480x16 -dpi 96 -ac -kb

2. Set display for application that runs inside scratchbox:
   

   export DISPLAY=:2

3. You can now run the SDK UI. A Diablo or Fremantle desktop will appear in your Xephyr window:
   

   af-sb-init.sh start

4. Now you are ready to run any Maemo or Maemo Qt application with:

   run-standalone.sh ./qtapps

Note: run-standalone.sh sets some variable needed by Qt to use the Hildon style.

Device

Maemo Qt applications are Linux binaries. They can run on the device without any problem if you copy them to "partitions" mounted with exec flag. (for example, /home/user or /opt in Fremantle).

Fore example, if we want to run quassel (Qt IRC Client) we have to launch it with:

su -c ./quassel user

File:Hammer.png Porting Qt applications to Maemo

Porting a Qt desktop application to Maemo requires very little effort. This is because the Maemo Qt libraries will take care of giving the Hildon look & Feel and enabling the virtual input methods for your application.

Overriding the Qt Maemo changes

Maemo Style

Hildon Style is the default Qt application style. Other style available are:

• QCleanLooks
• Windows
• Plastique

Qt application can use other Qt styles;

• Running your application with the style flag:

./qt-test-application -style windows

• Using QApplication::setStyle( QStyle * style )

• If you want to change the style of a widget:QWidget::setStyle( QStyle * style )

Showing the status bar

Hildon applications don't have a status bar. Qt for Maemo hides the status bar by default.

You can show it again by using method statusBar()->show() in your class derived from QMainWindow.

Using the Kinetic Finger Scrolling (cf Gtk's PannableArea)

See Finger Scrolling

Adding Maemo changes to a Qt Application

Some methods of Qt for Maemo are not available in the "standard" Qt libs, so a Qt application with specific Maemo Qt code can't be built outside the Maemo SDK. To avoid this issue, the developer can use the preprocessor directives:

In the source code:

#ifdef Q_WS_MAEMO_5
   //specific hildon/maemo5 code here
#endif

In the project file:

maemo5 {
   message("Hello Hildon")
   SOURCE += hildon.cpp
   HEADER += hildon.h
   FORMS   += hildon.ui
}

Home widget interaction

Limitations

Currently Qt Maemo lacks full support for Hildon widgets introduced in Maemo 5.

At the moment, creating a Qt application that follows Maemo 5 UI Style requires using custom Qt widgets, coded within the application itself.

There is work ongoing to provide Qt Hildon widgets for Maemo 5, see Qt Hildon Widgets

To get the benefits of the ongoing Maemo 5 hildon integration work in Qt, you must get the latest Qt source code and compile it yourself. See Building Qt from GIT repository.

File:Bug.png Debugging a Qt application

Note: Fremantle Gdb 6.8 crashes in x86 and gives messed up backtraces on the device. Using gdb 7.0 is recommended. You can get gdb 7.0 sources from http://ftp.de.debian.org/debian/pool/main/g/gdb/gdb_7.0.orig.tar.gz, compile it (./configure && make) inside X86 and armel scratchbox targets. Here you can find GDB7 for fremantle x86 and armel.

/usr/local/bin/gdb7 ./myapp

File:Chart.png Profiling a Qt application

OProfile

Valgrind

File:Package.png Packaging a Qt application for Maemo

File:Helmet.png Maemo Qt API Reference

Maemo Qt is based on Qt for X11. It shares same APIs avoiding API breaks. In this way every Qt application that runs in other platforms (Windows, Mac OS X, Linux, S60, etc.) can run in Maemo devices as well. To Develop a Qt application you can use the Official Qt 4.6 for Maemo API documentation and the list below to see what are the Maemo changes.

Here are examples that show several maemo5 Qt widgets in Qt 4.6.

http://qt.nokia.com/doc/qt-maemo-4.6/examples-maemo5.html

http://qt.gitorious.org/+qt-developers/qt/x11-maemo/trees/986340bb5e4b69ceb0a959c2a067a1ed5e504d50/examples/maemo5/widgets

Finger Scrolling

Kinetic scrolling is present by default in most scrolling widgets, eg. QTextBrowser, QTableView. If you want to tweak the kinetic scrolling parameters like inertia and acceleration then you can instaniate a QAbstractKineticScroller object like this:

QAbstractKineticScroller ks =  
  scrollArea->property("kineticScroller").value<QAbstractKineticScroller *>();

where scrollArea could be QScrollArea with some widgets added to it, or you could use implementations like QTextBrowser.

You can tweak scrolling like this:

ks->setDragInertia( (double)value / 100.0)
ks->setMode(QAbstractKineticScroller::PushMode)

etc., refer to the examples here for details: http://qt.gitorious.org/+qt-developers/qt/x11-maemo/blobs/4.6-fremantle/examples/maemo5/kineticscroller/main.cpp

Orientation

Official documentation

Maemo5 Readme file

There is a README file in Qt 4.6 source tree.

File:Helmet.png Contributing to the Maemo Qt Project

Maemo Qt is a community project. Contributing to the forum, sending us patches, give us feedbacks, tracking bugs are all activities that help us to improve the quality of our work.

Here there is a list of things that every person interested in helping us should read.

Stay updated

Any Maemo Qt developer should be updated and should participate to the discussions, for that he must join the Mailing list. BTW the mailing list is not for Maemo Qt Developers but it's open to Maemo Qt application developers too.

Introduction to Git

If you are a git newbie you maybe find interesting these links:

• http://www.sourcemage.org/Git_Guide
• http://www.gitcasts.com/
• http://www.gnome.org/~newren/eg/git-for-svn-users.html
• Using the git protocol through a HTTP CONNECT proxy: http://www.emilsit.net/blog/archives/how-to-use-the-git-protocol-through-a-http-connect-proxy/

Understanding the structure of our Git repository

Preparation

Make sure each scratchbox target has

 fakeroot apt-get build-dep libqt4-gui

(you may need to apt-get install libgl-dev too as it's not in the Build-Depends: yet)

Building Qt from Git repository

1. Clone the repository:
   

   git clone git://gitorious.org/+qt-maemo-developers/qt/qt-maemo.git

   
   or if you are a member of our team:
   

   git clone git@gitorious.org:+qt-maemo-developers/qt/qt-maemo.git

2. Change dir:
   

   cd qt-maemo

3. Copy the remote 4.5 branch in your working copy:
   

   git checkout -b 4.5 origin/4.5

4. Checkout ONE of these branches:
   

   git checkout -b qt-diablo origin/qt-diablo

   
   

   git checkout -b qt-n900+w34 origin/qt-n900+w34

   
   

   git checkout -b qt-mer origin/qt-mer

5. Build the packages:
   

   dpkg-buildpackage -rfakeroot -b

Merging branches changes in the mainline [OLD]

Before to merge your changes in the mainline, the code must be full working, cleaned and tested. A review from another developer is also needed in order to reduce the possibility to add errors.

QML

QML is a GUI interface building scripting language for Qt. Check out the QML calculator example.

File:Help-contents.png F.A.Q.

I'm trying to compile a Qt application for ARMEL, but I got the error below. What's wrong?

/targets/FREMANTLE_X86/usr/include/qt4/QtCore/qatomic_i386.h:127: error: impossible constraint in 'asm'

You are using x86 include files, then you have to update your Makefile. Running qmake before make will be solve this issue.

I'm trying to compile a Qt packcage for x86, but I got the error below. What's wrong?

In file included from maemo/gconfsymbols.cpp:41:

Your scratchbox does not have /bin/sh, so when calling pkg-config from qmake, CFLAGS and LIBS are not set correctly. Running ln -s /scratchbox/tools/bin/sh /bin/sh will be solve this issue.

I'm trying to compile a diablo Qt package, so I just created a symbolic link, debian, for debian.diablo, and then run dpkg-buildpackage command, but I got a build error because the symbolic link was deleted

When running dpkg-buildpackage, all symbolic links will be deleted, so need to rename the folder from debian.diablo to debian to make a build of diablo Qt package.

I installed Qt (libqt4-dev) to scratchbox and tried to build a sample application, but I got the error because some header files such as qhildonstyle.h, and qvfbhdr.h etc. were missing

libqt4-dev should copy all header files, but now, at least in 4.5.2-1maemo1, some files are missing. Please download file below and extract to your scratchbox system.

http://qt4.garage.maemo.org/patches/qt4-missing-header.tgz