Qt

To define the default Qt toolkit, you can create QT_SELECT environment variable. For example, to use Qt 4, set .

You can set the default Qt toolkit by creating a symlink to one of .conf files in directory. For example, to set Qt 4 symlink to :

$ ln -s  

Qt 5 decides the style to use based on what desktop environment is used:

• In KDE Plasma, it uses the actually selected Qt style. It can be configured using KDE System Settings (systemsettings), the settings can be found in Appearance > Application Style > Widget Style.
• In Cinnamon, GNOME, MATE, LXDE, Xfce, it uses GTK (QGtkStyle).
• In other desktop environments, it uses Fusion.

To force a specific style, you can set the environment variable. Specifically, set it to if you want to use the GTK theme (Note: you will need to install the Qt style plugins mention below to get the GTK style). Qt 5 applications also support the flag, which you can use to launch a Qt 5 application with a specific style.

The following styles are included in Qt 5: Fusion, Windows. Others can be installed separately:

• Oxygen — KDE Oxygen style.

https://invent.kde.org/plasma/oxygen || oxygen

• Kvantum — customizable SVG-based theme engine with a variety of built-in styles, including imitations of some popular GTK themes such as Adapta, Arc, Ambiance

https://github.com/tsujan/Kvantum/tree/master/Kvantum || kvantum

Qt 4 application will try to mimic the behavior of the desktop environment they are running on, unless they run into some problems or hard-coded settings.

• In KDE Plasma, it uses the actually selected Qt style. It can be configured using KDE System Settings (systemsettings), the settings can be found in Appearance > Application Style > Widget Style.
• In Cinnamon, GNOME, Xfce, it uses GTK (QGtkStyle).
• In other desktop environments, it uses Windows.

For those who want to change the look and feel of Qt 4 applications, the Qt Configuration (qtconfig-qt4) GUI tool is provided by the qt4^AUR package. It offers a simple interface to configure the appearance of Qt 4 applications including style, colors, fonts and some further options.

Qt keeps all its configuration information in (system-wide) or (user-specific). The file is rather difficult to navigate because it contains a lot of information not related to appearance, but for any changes you can just add to the end of the file and overwrite any previous values (make sure to add your modification under the [Qt] header).

For example, to change the theme to QtCurve, add:

The following styles are included in Qt 4: CDE, Cleanlooks, GTK, Motif, Plastique, Windows. Others can be installed separately:

• Breeze — Artwork, styles and assets for the Breeze visual style for the Plasma Desktop.

https://invent.kde.org/plasma/breeze || breeze-kde4^AUR

An interesting way of customizing the look and feel of a Qt application is using Style Sheets, which are just simple CSS files. Using Style Sheets, one can modify the appearance of every widget in the application.

To run an application with a different style just execute:

$ qt_application -stylesheet style.qss

For more information on Qt Style Sheets see the official documentation or other tutorials. As an example Style Sheet see this Dolphin modification.

If you have GTK and Qt applications, their looks might not exactly blend in very well. If you wish to make your GTK styles match your Qt styles please read Uniform look for Qt and GTK applications.

Unlike Qt 4, Qt 5 does not ship a qtconfig utility to configure fonts, icons or styles. Instead, it will try to use the settings from the running desktop environment. In KDE Plasma or GNOME this works well, but in other less popular desktop environments or window managers it can lead to missing icons in Qt 5 applications. One way to solve this is to fake the running desktop environment by setting or , and then using the corresponding configuration application to set the desired icon set.

Another solution is provided by the package, which provides a Qt 5 QPA independent of the desktop environment and a configuration utility. After installing the package, run to set an icon theme, and set the environment variable so that the settings are picked up by Qt applications. Alternatively, use as argument to the Qt 5 application.

qt5ct-kde^AUR provides a patched qt5ct with better integration to KDE applications, including KDE QML applications.

If the errors below are received, and some icons still do not appear in some of the applications, install and :

Icon theme "oxygen" not found.
Icon theme "oxygen" not found.
Error: standard icon theme "oxygen" not found!

Qt supports most platforms that are available today, even some of the more obscure ones, with more ports appearing every once in a while. For a more complete list see the Qt Wikipedia article.

First of all, you need an Android SDK and NDK from AUR or using Android Studio.

SDK requires OpenJDK too. Diffenent Qt versions have different version requirements, check here for detail.

Next you are going to need Qt 5 for Android. You can install it from AUR as described below or build it yourself, you can find build instructions on Qt wiki page.

In case of problems you may want to visit known issues.

• - armeabi-v7a
• - aarch64
• - x86
• - x86_64

Alternatively, you can use the official Qt installer.

The following are official Qt tools:

• Qt Designer — A powerful cross-platform GUI layout and forms builder for Qt widgets.

https://doc.qt.io/qt-5/qtdesigner-manual.html || Qt 5: qt5-tools, Qt 4: qt4^AUR

• qmake — A tool that helps simplify the build process for development project across different platforms, similar to cmake, but with fewer options and tailored for Qt applications.

https://doc.qt.io/qt-5/qmake-manual.html || Qt 5: qt5-base, Qt 4: qt4^AUR

Qt has bindings for all of the more popular languages, see https://wiki.qt.io/Language_Bindings for a full list.

The following examples display a small 'Hello world!' message in a window.

• Package: qt5-base
• Website: https://www.qt.io/developers/
• Build:
• Run with:

• Package: .
• Website: https://doc.qt.io/qt-5/qtquick-qmlscene.html
• Run with: qmlscene hello.qml

• Package: - Python 3 bindings

• Website: https://riverbankcomputing.com/software/pyqt/intro
• Run with: .

• Package:
• Website: https://wiki.qt.io/Qt_for_Python
• Run with: python hello-pyside.py

See QtSharp.

When using KDE and/or any other Qt desktop environment debug info may be frequently be logged in the systemd journal.

Set as environment variable to change this behaviour, e.g. to completely disable logging:

To disable only debug logging, use .

Since Qt 5.1 SVG support has moved into a module. Since qt5-base does not depend on qt5-svg it may happen that the qt5-base is installed but not qt5-svg. This results in deceptive icon theme behaviour. Since SVG is not supported the icons are silently skipped and the icon theme may seem to be unused. Installing qt5-svg explicitly solves the problem.

As the user theme file (), are not read by other accounts, the selected theme will not apply to X applications run as root. Possible solutions include:

• Create symlinks, e.g
• Configure system-wide theme file:
• Adjust the theme as root

If pure Qt 4 (non-KDE) applications do not stick with your selected Qt 4 style, then you will probably need to tell Qt 4 how to find KDE's styles (Oxygen, Phase etc.). You just need to set the environment variable . E.g.:

QT_PLUGIN_PATH=$HOME/.kde4/lib/kde4/plugins/:/usr/lib/kde4/plugins/

should then be able to find your kde styles and everything should look nice again!

Alternatively, you can symlink the Qt 4 styles directory to the KDE4 styles one:

# ln -s /usr/lib/{kde,qt}4/plugins/styles/theme_name

If you get an error similar to

Qt FATAL: Cannot mix incompatible Qt library (version 0x50900) with this library (version 0x50901)

then you are most likely using a Qt 5 platform theme or style plugin which has not been recompiled against the latest version of Qt 5. These usually use Qt private headers which means they depend on an exact version of Qt and not just a matching soname. Figure out which theme/style you are using by checking the and environment variables, and rebuild the AUR package that provides it.

Create a file with such content :

See HiDPI#Qt 5.

If you have set the right keyboard configuration and dead keys are working in GTK apps (or other widget toolkits) but not in KDE or any Qt apps, then you might not have the proper compose file loaded in your Xorg session.

A way to confirm that is to:

1. launch a Qt app with qt.xkb.compose.debug logging rule enabled, eg. launching :
2. then try to write a character using a dead key, eg. <dead_circumflex> <e> for (LATIN SMALL LETTER E WITH CIRCUMFLEX)
3. if you encounter then you probably have this issue.

To fix this, first identify your locale. Then, if your locale doesn't have its own folder in , eg. , look for it in the mapping file to find the corresponding compose file (eg. ):

Now create or edit ~/.XCompose to include this compose file:

Finally, restart your Qt app, dead keys should be working and error should have disappeared whenever you debug with .