Qt4 development

= 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.

= 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  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

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

= 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.

Maemo Style
Hildon Style is the default Qt application style. Other style available are:
 * QCleanLooks
 * Windows
 * Plastique

Qt application can use other Qt styles; ./qt-test-application -style windows
 * Running your application with the style flag:


 * 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, for example:

//Specific hildon/Maemo5 code here
 * Qt 4.5 (Diablo and Fremantle)
 * 1) ifdef Q_WS_HILDON
 * 1) 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 }

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 {}".
 * Qt 4.6 (Fremantle)

//specific hildon/maemo5 code here
 * 1) ifdef Q_WS_MAEMO_5
 * 1) endif

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

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.

= 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

= Profiling a Qt application =

Valgrind
= Packaging a Qt application for Maemo =

= 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  #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
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.

//Includes for portrait mode support 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);
 * 1) ifdef Q_WS_HILDON
 * 1) include 
 * 2) include 
 * 3) include 
 * 4) endif
 * 1) ifndef Q_WS_HILDON
 * 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. , . If you want to tweak the kinetic scrolling parameters like inertia and acceleration then you can instaniate a   object like this:

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

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

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.

= 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/

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.

= 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  before   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, so when calling   from  ,   and   are not set correctly. Running   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