Some terminology: widget refers to what the user will see on their desktop, and plasmoid refers to the package you will create by following this tutorial. The distinction is not very strong, since a plasmoid always shows a widget, and the terms can be used interchangably to a certain extent. Just remember that "widget" is what the user will see.
The only required part of the structure, in fact, is the contents directory - almost everything will go in this directory. But separating your code into a different directory from application data is a good habit to have.
This metadata.desktop file list important information needed by Plasma to load the widget, and also information about what the widget is and who created it.
Comment gives a more detailed description of the widget. This is also displayed in the Add Widget dialog, and can be translated in the same way as Name.
Icon gives the name of the icon to associate with this plasmoid. The icon is shown in the Add Widget dialog. It must be the name of an icon that is either distributed with KDE (such as chronometer) or provided by your plasmoid.
The Type, X-KDE-ServiceTypes, X-Plasma-API and X-Plasma-MainScript fields are required for Plasma to find your plasmoid and know what to do with it. Note that X-Plasma-MainScript is a path relative the contents directory.
X-Plasma-DefaultSize specifies the default size for widget, as width,height. While the units aren't technically pixels, they have the same value as pixels providing you don't do anything like zoom in or out on your desktop.
X-KDE-PluginInfo-Category gives a category for the widget. This is used in the Add Widgets dialog to group and filter widgets. The value must be one of the category names listed at Projects/Plasma/PIG.
X-KDE-PluginInfo-Name is the internal name of the plasmoid (you can think of this as the name of the plasmoid, as opposed to the name of the widget which is given by Name). This is the name you will use as an argument to plasmoidviewer or plasmapkg when you need to provide a plasmoid name rather than a path. It doesn't have to be the same name as the directory containing metadata.desktop.
X-KDE-PluginInfo-Author, X-KDE-PluginInfo-Email, X-KDE-PluginInfo-Version, X-KDE-PluginInfo-Website and X-KDE-PluginInfo-License are informational, and are displayed in the About dialog for the plasmoid (which can be viewed by clicking the information icon next to the corresponding widget in the Add Widgets dialog of plasma).
X-KDE-PluginInfo-EnabledByDefault and X-KDE-PluginInfo-Depends rarely need to be changed from the values given here.
layout = new LinearLayout(plasmoid);
label = new Label(); layout.addItem(label);
plasmoid is a global variable that represents your widget. It has some useful methods that we'll come to in later tutorials.
First, we create a layout, because plasmoids don't have a layout by default. This just makes sure that the label is the correct size and in the correct place. Passing plasmoid to the LinearLayout attaches the layout to the widget.
Next we add a label to the layout, and finally we set the label text.
Note that with KDE 4.2, you will have to install the plasmoid first (see below). After that, you can run plasmoidviewer with the name of the plasmoid given by X-KDE-PluginInfo-Name in metadata.desktop. For example:
plasmapkg -i .
The final argument to plasmapkg is the path to the directory containing metadata.desktop and the contents directory.
You can now add your widget to the desktop using the Add Widgets dialog, or view it by running
To uninstall the plasmoid, use plasmapkg again with its -r option:
Note that while the argument to plasmapkg -i is a file or directory, you need to pass the plasmoid name (given by X-KDE-PluginInfo-Name in metadata.desktop) to plasmapkg -r.