Qt4 Hildon Legacy

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=== What is Hildon? ===
=== What is Hildon? ===
Hildon is an application framework for Linux operating system mobile devices (PDAs, mobile phones, etc), developed by Nokia for Maemo and now a part of GNOME, that focuses on providing a finger friendly interface.<ref>[http://en.wikipedia.org/wiki/Hildon on Wikipedia]</ref>
Hildon is an application framework for Linux operating system mobile devices (PDAs, mobile phones, etc), developed by Nokia for Maemo and now a part of GNOME, that focuses on providing a finger friendly interface.<ref>[http://en.wikipedia.org/wiki/Hildon Hildon on Wikipedia]</ref>
[http://live.gnome.org/Hildon Read more...]
[http://live.gnome.org/Hildon Read more...]

Revision as of 09:42, 20 April 2009



File:Intro.png Intro

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, and GNOME.[1]


What is Hildon?

Hildon is an application framework for Linux operating system mobile devices (PDAs, mobile phones, etc), developed by Nokia for Maemo and now a part of GNOME, that focuses on providing a finger friendly interface.[2]


Developing on Maemo

Developing applications for Maemo is done with the Maemo SDK. The process from creating the first prototype of your application to distributing to a wide audience consists basically of three steps:

  • Share your application project in the Garage.
  • Make your application easy to install and put in the Extras.
  • Once your application has a high quality - be promoted to the Nokia user site.


Maemo SDK

The Maemo SDK is based around the Debian-oriented Scratchbox Cross Compilation Toolkit, which provides a sandbox environment in which development may take place. Scratchbox uses Qemu to emulate an ARMEL processor or sbrsh to remotely execute instructions. Scratchbox-compatible rootstraps are available for both x86 and ARMEL, so the majority of development and debugging takes place on x86, with final packaging being for ARMEL.[3]

Watch the Maemo SDK in action!

What is Scratchbox?

Scratchbox is a cross compilation toolkit designed to make embedded Linux application development easier. It also provides a full set of tools to integrate and cross compile an entire Linux distribution.[4]


File:Rocket.png Getting started

To start to develop with Maemo Qt, we need to install the Maemo SDK on a Linux machine.

Hey, I don't have a Linux machine!

That's not a big problem. [Maemo SDK Virtual Image project provides a virtual development image for the Maemo platform that can be used with VMPlayer.

Installing the Maemo SDK

See the SDK documentation for details on installing the SDK.

If you are on a non-debian system such as openSUSE you might need to perform the following command in another shell prior to logging in in order to get ARM CPU emulation working:

sudo /scratchbox/sbin/sbox_ctl start

Installing the Qt packages in Scratchbox

After Scratchbox and the SDK are installed and working, you need to login, add the Extras and Extras-devel repositories to your apt-get sources and install the Qt libs. Paste this into your Scratchbox shell (without the ">" prompt):

>> echo "# Maemo extras and extras-devel
deb http://repository.maemo.org/extras/ diablo free non-free
deb-src http://repository.maemo.org/extras/ diablo free
deb http://repository.maemo.org/extras-devel/ diablo free non-free
deb-src http://repository.maemo.org/extras-devel/ diablo free" >> /etc/apt/sources.list

Then run these commands to update the catalog:

>> apt-get update
> fakeroot apt-get install libqt4-gui
> fakeroot apt-get install libqt4-dev

Do these steps for the DIABLO_X86 and the DIABLO_ARMEL target if you plan to build on both.

How to compile a Qt application in scratchbox

All the Qt tools you need are available in scratchbox. In order to compile a Qt application you need to follow the standard Qt way:

qmake -project
qmake file.pro

Running a Qt application in scratchbox


Running a Qt application on device

To run a Qt application into the device, we need to copy it there.

Installing OpenSSH server on the device

To install and run applications on the device, we'll need to install an SSH server.

  • Open the Application Manager.
  • Make sure Extras is enabled.
  • Install openssh-server from the list.

Setting up a network connection

We can connect to device to our working machine via WLAN or USB. Connecting the device to a WLAN is quite easy, but USB networking is more difficult to set up.

Using scp to copy the excutable on the device

scp or secure copy is a common Linux application. It can copy files or a directories over a secure connection. To copy our application on the device we just need to run it with a syntax like this:

PC_$> scp qtApplication root@DEVICE-IP:/home/user

Executing the application

Now that the application has been copied onto the device, we can run it. For that we need to open the terminal or we can use ssh from our PC.

PC_$> ssh root@DEVICE-IP
N810_#> su - user
N810_$> ./qtApplication

File:Hammer.png Porting a Qt application in Maemo


Porting a Qt desktop application to Maemo requires very little effort. This 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

The Maemo style is the default style of Qt applications on Maemo. The other styles available in Qt 4.4 Maemo are QCleanLooks, Windows and Plastique (It will be available in the next release of Qt).

You can force your application to use another style in several ways:

  • Running your application with the flag -style <style_name>

HINT: You can put this flag in the Exec field of the desktop file that launch the application.

$> ./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 modifying your code.


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:

#ifdef Q_WS_HILDON
   //Specific hildon code here 



File:Bug.png Debugging a Qt application



The GNU Project Debugger, or gdb for short, is a general purpose debugger that can be used for various debugging purposes.

Debugging a Qt application in Scratchbox


Debugging a Qt application on device

  1. Installing gdb on the device.
    1. Add the SDK tools repository to the catalogue list.
    2. install gdb by using apt-get (require around 6 MB of space)
  2. Install the debug symbols files in scratchbox (ARMEL target)
  3. apt-get install libqt4-dbg
  4. Run the application (device side)
  5. $gdbserver ./qtApplication
  6. Run the gdb client on your host PC (scratchbox side)
  7. [sbox-DIABLO_ARMEL: ~/TEST/svn/qt4-x11-4.4.0/examples/widgets/tablet] > gdb ./qtApplication
  8. Set the target of gdb
  9. (gdb) target remote
  10. Tell to gdb to continue to debug the application on the device
  11. (gdb) continue
  12. Wait some moments...
  13. Your application will appear on the device screen. Happy debugging!


File:Chart.png Profiling a Qt application


OProfile is a low overhead system-wide profiler for Linux. It can be used to find CPU usage bottlenecks in the whole system and within processes. It works fine in the device, but viewing the reports can take quite a long time (10 minutes) when fired up on N800/N810 devices. Therefore, it often makes sense to run opreport in scratchbox.

If you want to know more about OProfile in Maemo see the documentation.



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 the same API avoiding API breaks. In this way every Qt application that runs in other platforms (Windows, Mac OS X, Linux, S60, etc.) can run also into the Maemo devices. To Develop a Qt application you can use the Official Qt 4.4 API documentation and the list below to see what are the Maemo changes.

 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.
   For a password field we need to set a specific IM mode:
   QInputContext qic = widget->inputContext();
 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>
 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);
           return d->edit->inputMethodQuery(query);

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.

Commit changes in SVN

If you are a Maemo Qt developer and you want to save your changes in the Garage SVN but your project is not ready to go to the main line (trunk/qt-x11), you should create a private branch and then work there until the merging with the mainline.

For that you have to create a your directory in branches/ named developer_name-qt. After that you can copy trunk/qt-x11 in your directory.

svn copy --username developer_name https://garage.maemo.org/svn/qt4/trunk/qt-x11 https://garage.maemo.org/svn/qt4/branches/developer_name-qt -m "Creating private branch of trunk/qt-x11"

NOTE: Subversion uses cheap copy, so them don't increase the size of the repository. Then feel free to create your own branch.

Merging branche changes in the mainline

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.

Be updated

Any Maemo Qt developer should be updated and should participate to the discussions, for that he must join the Mailing list.

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

I'm tring 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 tring 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.


  1. Maemo Platform on Wikipedia
  2. Hildon on Wikipedia
  3. Maemo SDK on Wikipedia
  4. Scratchbox on Wikipedia