Qt4 development

Contents

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.

Maemo platform

The Maemo platform is the software stack for Nokia Internet Tablets, which includes the Maemo operating system and the Maemo SDK. The Maemo Platform is mostly based on open source code, and has been developed by the Maemo Software department within Nokia in collaboration with many open source projects such as the Linux kernel, Debian, Hildon and GNOME.

Read more about the Maemo platform and a developer overview.

File:Rocket.png Getting started

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

Installing Qt packages in Scratchbox

Maemo Qt developers offers a set of Qt packages for Fremantle (Maemo5 - OS2009) and Diablo (Maemo4.1 - OS2008).

Fremantle

You do not need to add any extra repository for Fremantle since Qt packages are already available in the SDK. You can install Qt with the command: 

fakeroot apt-get install libqt4-dev

Using Qt 4.6 in Fremantle

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

Diablo

Diablo Qt packages are into the official Extras repository. In order to start to develop with those packages you need to add extras repository to your repository list, and then install Qt packages in the terminal: 

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

Because of some issue with CMake, Diablo CMake packages are currently useless since CMake segfaults (on the device at least). This issue has been solved in Fremantle and CMake packages that comes from Fremantle SDK work nicely.

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:

Qt application can use other Qt styles;

  • Running your application with the style flag: 
./qt-test-application -style windows

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, for example:

  • Qt 4.5 (Diablo and Fremantle) 
#ifdef Q_WS_HILDON
   //Specific hildon/Maemo5 code here 
#endif

Qt project files can load hildon files using: (check qmake ref guide for more info about qmake options) 

contains(QT_CONFIG, hildon): {
   message("Hello Hildon")
   SOURCE += hildon.cpp
   HEADER += hildon.h
   FORMS   += hildon.ui

}

  • Qt 4.6 (Fremantle)

Q_WS_HILDON has been replaced by Q_WS_MAEMO_5 in Qt 4.6 and Qt 4.5 "contains(QT_CONFIG, hildon):{}" does same job of Qt 4.6 "maemo5 {}". 

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

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

Home widget interaction

Main article: Qt4 and Hildon 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

Main article: Documentation/Maemo_5_Developer_Guide/Kernel_and_Debugging_Guide/Maemo_Debugging_Guide


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

Main article: Documentation/devtools/maemo5/oprofile


Valgrind

Main article: Documentation/devtools/maemo5/valgrind



File:Package.png Packaging a Qt application for Maemo

Main article: Packaging a Qt application


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 4.5 API documentation and the list below to see what are the Maemo changes.

Diablo

 QString QDesktopServices::storageLocation(StandardLocation type) returns specific Maemo locations for these types:
 - DesktopLocation:   QDir::homePath() + QLatin1String("/MyDocs"),            instead of QDir::homePath() + QLatin1String("/Desktop")
 - DocumentsLocation: QDir::homePath() + QLatin1String("/MyDocs/.documents"), instead of QDir::homePath() + QLatin1String("/MyDocs/.documents")
 - PicturesLocation:  QDir::homePath() + QLatin1String("/MyDocs/.images"),    instead of QDir::homePath() + QLatin1String("/Pictures")
 - MusicLocation:     QDir::homePath() + QLatin1String("/MyDocs/.sounds"),    instead of QDir::homePath() + QLatin1String("/Music")
 - MoviesLocation:    QDir::homePath() + QLatin1String("/MyDocs/.videos"),    instead of QDir::homePath() + QLatin1String("/MyDocs/.videos")

 QTabletEvents are able to get the pressure value from the touchscreen.
  - The eventdeviceType is for the touchscreen is set to QTabletEvent::Stylus.
  - QTabletEvents won't be used anymore in Fremantle
 
 Finger poke is emulated in scratchbox by the Middle Mouse button (NOTE: There is no Fullscreen VKB in scratchbox)

 QInputEvents don't move the cursor. 
 It's mandatory to get working the HIM moving the cursor via QInputMethodEvents.
 Why is it mandatory?  
 Because if the user select text with the finger from the right to the left, we are able to remove the highlighted text, but the
 cursor will be moved on the last char instead to stay on the first one.
  
 To do that some changes has been added to some widget function like: widget::inputMethodEvent(QInputMethodEvent *e).
 Modifing that function in some custom widgets may be necessary.
 Don't reimplementing that function will break some fullscreen virtual keyboard features.
 
 Hardcoded Keys:
 In the QMainWindow:
 - F6 - Toggle fullscreen the application
 - F4 - Shows/Hides the application context menu
 - Zoom in  - is a standard key sequence QKeySequence::ZoomIn
 - Zoom out - is a standard key sequence QKeySequence::ZoomOut

 Input Method:
 Maemo Qt uses the Hildon IM as default Input method.
 Each kind of widget can set the IM mode. This allows the input method to focus on the type of input that the application is expecting.
 Eg: spinboxes can receive only numeric characters (1-9).
 
 NOTE: Qt widgets like QTextEdit, QLineEdit... set the right input method mode automatically. 
 
 A developer can change it by using:
   void QInputContext::setInputMode(int mode);
 It will update immediately the Hildon Input method to use the selected IM mode.  
 
 HIC Modes:
   HILDON_GTK_INPUT_MODE_ALPHA 	alphabetical characters and whitespace
   HILDON_GTK_INPUT_MODE_NUMERIC 	numbers 0-9 and the '-' character
   HILDON_GTK_INPUT_MODE_SPECIAL 	special characters
   HILDON_GTK_INPUT_MODE_HEXA 	hexadecimal characters; numbers 0-9, characters a-f, and A-F
   HILDON_GTK_INPUT_MODE_TELE 	telephone numbers; numbers 0-9, whitespace, and the characters "pwPW/().-+*#?,"
   HILDON_GTK_INPUT_MODE_FULL 	unrestricted entry mode, combination of the alpha, numeric and special modes.
   HILDON_GTK_INPUT_MODE_MULTILINE 	the client contains multiple lines of text or accepts linebreaks in the input.
   HILDON_GTK_INPUT_MODE_INVISIBLE 	do not echo or save the input in the IM when entering sensitive information such as passwords.
   HILDON_GTK_INPUT_MODE_AUTOCAP 	automatically capitalize the first letter at the start of a sentence.
   HILDON_GTK_INPUT_MODE_DICTIONARY 	enable predictive dictionaries and learning based on the input.
  
 Example:
   For a password field we need to set a specific IM mode:
   int mode = HILDON_GTK_INPUT_MODE_FULL | HILDON_GTK_INPUT_MODE_INVISIBLE
   QInputContext *qic = widget->inputContext();
   qic->setInputMode(mode);
 
 If you are developing a Custom widget able to receive input text, you can instruct your widget to use the right IM Mode just returning
 the mode.
 
 - How does it work?
 The Hildon IM sends a XMessage to pop up the "Virtual Keyboard" (or better the Main HIM UI) when an input widget receive the focus.
 The IM before to raise the VKB, makes an inputMethodQuery to the widget retrieving the IM mode.
 If the developer of the custom widget doesn't set the mode property, the IM will use HILDON_GTK_INPUT_MODE_FULL (the default mode) for that widget.
 
 Setting the ImMode is quite easy. Check the code below for more understanding.
 
 #ifdef Q_WS_HILDON
 #include <QInputContext>
 #endif
 
 QVariant QAbstractSpinBox::inputMethodQuery(Qt::InputMethodQuery query) const
 {    
   Q_D(const QAbstractSpinBox);
   switch(query) {
       case Qt::ImMode:{
           int mode = HILDON_GTK_INPUT_MODE_NUMERIC;
           return QVariant(mode);
       }
       default:
           return d->edit->inputMethodQuery(query);
   }
 }

FREMANTLE (Qt 4.5)

Kinetic scrolling

Kinetic scrolling is enabled by default in QListWidgets and is supported by any Qt widget that inherits QScrollArea. Any item view widgets (QTreeView/QTreeWidget, QListView, QTableView/QTableWidget...) can use fingerscroll if it has "FingerScrollable" dynamic property set to true. Eg: 

 QTableWidget *table = new QTableWidget(this);
 table->setProperty("FingerScrollable", true);

NOTE: Available in Qt > 4.5.3-xxxxx-maemo4

Hildon-Desktop widgets

Main article: /Qt Hildon Widgets


They are supported by Qt. An example (qt-example-hildondesktopwidget) is available in extras-devel.

Hildon menus

Maemo5 menus are created using QActions available in menu bar. Hidden, disabled, separators and widget actions won't shown. (Same in Qt 4.6)

  • qt-4.5.3-xxxx-maemo4 packages - needs QActions in a "fremantle" menu.
  • Pkgs > qt-4.5.3-xxxx-maemo4 shows Maemo5 menus automatically

Note: Maemo5 policy doesn't allow application to have more than 10 items.

Stackable windows

http://maemomm.garage.maemo.org/docs/tutorial/figures/stackable-window.png Are supported by Qt. To create them you need to create a MainWindow child of another Main window. 

QMainWindow *fistStackableWindow = new QMainWindow;
QMainWindow *secondStackableWindow = new QMainWindow(fistStackableWindow);

// you need the below line to see the back button on the top right hand corner of the stacked window instead of a cross 

secondStackableWindow->setAttribute(Qt::WA_Maemo5StackedWindow);


Note: this is not entirely accurate, see

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

Raise a Qt application in background

QWidget::activateWindow() does the job.

Implemented in Qt packages >= qt-4.5.3-xxxx-maemo6

How to minimize a Qt application? 

QDBusConnection c = QDBusConnection::sessionBus();
QDBusMessage m = QDBusMessage::createSignal("/","com.nokia.hildon_desktop","exit_app_view");
c.send(m);

Portrait mode and listening for orientation changes

If you want to run your application in portrait mode then you can add these lines to your application. The code goes in your main widget constructor. 

#ifdef Q_WS_HILDON
//Includes for portrait mode support
# include <X11/Xlib.h>
# include <X11/Xatom.h>
# include <QtGui/QX11Info>
#endif

#ifndef Q_WS_HILDON
int value = 1;
Atom portraitSupport = XInternAtom(QX11Info::display(), "_HILDON_PORTRAIT_MODE_SUPPORT", false);
Atom portraitRequest = XInternAtom(QX11Info::display(), "_HILDON_PORTRAIT_MODE_REQUEST", false);
XChangeProperty(QX11Info::display(), winId(), portraitSupport, XA_CARDINAL, 32, PropModeReplace, (uchar *)&value, 1);
XChangeProperty(QX11Info::display(), winId(), portraitRequest, XA_CARDINAL, 32, PropModeReplace, (uchar *)&value, 1);
#endif

If you want to listen for orientation changes and then switch the view to landscape or potrait mode automatically than take a look at Maemo_Qt_Extra_Libraries for more information.

QDockWidgets

QDockWidgets are not finger friendly widgets. They should not be used in Maemo. In case you are porting an application to Maemo maybe you want to do few changes as possible into your UI. Then you could use QDockWidget::setFeatures(QDockWidget::NoDockWidgetFeatures); to hide float and close button and lock the position of the dock widget.

QPrint* and QSystemTray support missing 

Printing (QPrint*) and System tray support is missing in current
Qt 4.5.3-xxxx-maemo4 packages.
Since incompatibility with KDE and other Qt application, they will be enabled again in next Qt 4.5.3 packages.

QSplashScreen not fully compatible with Hildon-Desktop 

QSplashScreen's window type is not supported in Fremantle. The splash screen is
shown in full screen and the image is repeated to fill the splash screen's
window. When splash screen is closed normal window closing animation is shown
before showing the actual application window. For these reasons developers are
disencouraged to use splash screens in their applications.

As a workaround for the problem you can set a window property that tells HD to skip the transitions: 

static void set_no_transitions (Display *dpy, Window w)
{
Atom no_trans;
int one = 1;
no_trans = XInternAtom (dpy, "_HILDON_WM_ACTION_NO_TRANSITIONS", False);
XChangeProperty (dpy, w, no_trans,
                 XA_CARDINAL, 32, PropModeReplace,
                 (unsigned char *)&one, 1);
}

QToolBar limitations

Adding a QToolBar to a QMainWindow will always result in a toolbar at the bottom of the screen. (Justification/Workarounds?)



FREMANTLE (Qt 4.6)

Here an example that shows 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

QSplashScreen

Should be fixed in Qt 4.6. SplashWindow type is not supported by Fremantle WM. Qt 4.6 display splash screen using popup window type.

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:

Understanding the structure of our Git repository

Main article: Qt Maemo Git Process


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:
maemo/gconfsymbols_p.h:49:25: gconf/gconf.h: No such file or directory
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
Retrieved from "http://wiki.maemo.org/Qt4_development"