Writing a plasma applet in QML is very easy, in fact, with KDE 4.6 and Qt 4.7 it just works.
It is recommended that you have read through the Qt QML Tutorials, as there are quite a few and they are explained thoroughly. There is also a list of all standard QML elements.
Essentially, most of the content is the same. The exceptions to be noted are how data is gathered...since we use Data Engines, it is a bit different. Text color and font should be made to use PlasmaCore.Theme.
See the KDE Examples repository for more KDE-related helpful resources. Also of use (which use QML and Plasma) are: Plasma Mobile, Declarative Plasmoids (playground), for WIP ports of C++ originals
The root item can be anything that inherits QGraphicsItem. For example, in this case it is QGraphicsWidget which is a plasmoid. It can also simply be an Item. I also noticed that PathView does not respond to mouse inputs automatically (so flicking doesn't work). Probably because events are being intercepted. So take note, it'll have to be e.g. an Item, for that case.
Anchor layouts offer a nice way of grouping UI elements nicely together. The idea is that you connect edges or corners of one element to the edge or corner of another widget. Some examples:
import QtQuick 1.0
import org.kde.plasma.core 0.1 as PlasmaCore
Item {
width: 200
height: 300
Text {
id: first
text: i18n("1st line")
anchors { top: parent.top;
left: parent.left;
right: parent.right;
}
}
Text {
id: second
text: i18n("2nd line")
anchors { top: first.bottom;
left: parent.left;
right: parent.right;
bottom: parent.bottom;
}
}
}
You create a .desktop file and the .qml file. They have to be in the usual plasma package structure.
plasmoid-qml/metadata.desktop plasmoid-qml/contents/ui/main.qml
[Desktop Entry]
Name=Hello QML
Comment=A hello world widget in QML
Icon=chronometer
X-Plasma-API=declarativeappletscript
X-Plasma-MainScript=ui/main.qml
X-Plasma-DefaultSize=200,100
X-KDE-PluginInfo-Author=Frederik Gladhorn
X-KDE-PluginInfo-Email=gladhorn@kde.org
X-KDE-PluginInfo-Website=http://plasma.kde.org/
X-KDE-PluginInfo-Category=Examples
X-KDE-PluginInfo-Name=org.kde.hello-qml
X-KDE-PluginInfo-Version=0.0
X-KDE-PluginInfo-Depends=
X-KDE-PluginInfo-License=GPL
X-KDE-PluginInfo-EnabledByDefault=true
X-KDE-ServiceTypes=Plasma/Applet
Type=Service
import QtQuick 1.0
Text {
text: "Hello world!";
}
You can install your plasmoid: plasmapkg --install plasmoid-qml
You can run it in plasmoidviewer as usual: plasmoidviewer plasmoid-qml
It's possible to use Plasma specific imports in qml files loaded by qmlviewer:
qmlviewer -I /usr/lib/kde4/imports/ plasmoid-qml/contents/qml/main.qml
Where the -I is the path to the plasma plugin for qml. Try to look for the path of /usr/lib/kde4/imports/org/kde/plasma/graphicswidgets/libgraphicswidgetsbindingsplugin.so and use everything up to org of that path.
Hovewer it's strongly discouraged to use qmlviewer to develop plasmoids, because some features won't be available there:
In order to have a better integration with the KDE platform and to reach an higher degree of expressivity, the stock features of QML have been expanded with the following features, that strictly follow the Plasmoid JavaScript API:
if the root object of the plasmoid has the properties minimumWidth and minimumHeight, they will be used as the minimum size for the plasmoid. If they will change during the plasmoid execution, the plasmoid minimum size will be updated accordingly.
import QtQuick 1.0
Text {
property int minimumWidth: paintedWidth
property int minimumHeight: paintedHeight
text: "Hello world!";
}
In the above example, the minimum size is binded to the paintedWidth/paintedHeight properties of the Text element, ensuring there will always be enough room for the whole text to be displayed.
Every QML plasmoid will have an object called plasmoid, that will give access to the configuration, the formfactor, immutability and so on. It offers the same api as the object with the same name in the Javascript API.
For specific info on this, see Javascript API-Plasmoid Object
It's possible to localize strings with the usual i18n(), i18nc(), i18np() global functions
Some extra types are available from withing JavaScript, namely
To use some Plasma specific features it is necessary to use some particular QML imports. See Plasma QML API.
org.kde.qtextraimports To use, do:
import org.kde.qtextracomponents 0.1 as QtExtraComponents
To use standard plasma widgets (e.g. Plasma::LineEdit, etc.), you simply add an import line for them. All properties, signals and slots from ordinary Plasma widgets are available there. Those widgets are provided as a transition tool, intended to be replaced by the Plasma version of QtComponents.
import QtQuick 1.0
import org.kde.plasma.graphicswidgets 0.1 as PlasmaWidgets
Item {
width: 64
height: 64
PlasmaWidgets.IconWidget {
id: icon
Component.onCompleted: setIcon("flag-red")
anchors.centerIn: parent
}
}