Thursday, November 5, 2009


Ah, I've finally managed to make my new fresh Kubuntu 9.10 installation usable. Now it's time to do some KDE stuff and I'll show you how easy it's to create a plasmoid (applet/widget) for KDE4.

I've created a simple applet which shows the number of unread mail in a Gmail inbox. We already know how to fetch the list with unread mail, which I have explained in a previous blog post. Now I'll create a nice applet showing the count. I'm going to keep it as simple as possible, writing hard-coded values, skip error handling and so on to avoid making things more complicated than necessary.

There are several good tutorials at which explains plasma programming. They cover the basics and explains things in detail so I'll only make references to the pages instead of repeating what's already been written.

The first tutorial you should read (you don't have to read it right now, you can read it after you tried doing the applet) is Python Plasma Getting Started. The tutorial covers setting up a simple plasmoid, packaging, installing and running.

I'll name the plasmoid GMonitor because it only monitors the mailbox and shows the number of unread mail, it will not actually try to do some kind of notification (yet?!).

I've put the code on github, you can clone it with:
$ git clone git://
You'll find a Makefile in the git which can be useful when doing plasmoids. The Makefile supports installing, un-installing, viewing, packaging and updating the plasmoid.

The directory tree looks like this:
|-- Makefile
|-- contents
|   `-- code
|       `--
`-- metadata.desktop
The gmonitor directory is the project home and contents/code contains the python source. The metadata.desktop file will be explained below.

To be able to install and run your applet you need to provide a metadata.desktop file to plasma. The metadata.desktop file contains important information about the applet and you can read more about the file in the Plasma Getting Started tutorial.

Feel free to change the file. The Name specifies the applet name and the Icon field gives the name to the icon to associated with this applet. These two fields are typically shown when listing applets in the 'Add Widget' dialog. There are two important fields which must be present for plasma to run your applet, the X-Plasma-API field specifies which script-engine to be used and the X-Plasma-MainScript field which script to be executed. It's also good to know that the X-KDE-PluginInfo-Name fields is used as a plasmoid identification, so it should be unique.

Some notes about the implementation. There are two classes, GMonitor and MailFrame (I know, poor name). The MaiFrame class has an icon and a label. When the mail count is set to zero (by calling setCount(cnt)), the icon is disabled, grayed and the label is set to 'No new mail'. When the mail count is set to a value greater than zero, the icon is enabled, colored and the label is set to 'Count: x', where x is the number of mail in the inbox. See the images below.

Sample of what the applet looks like

When the icon is enabled and clicked, a 'clicked()' signal is emitted. The GMonitor class connects the openBrowser() method to the 'clicked()' signal. The openBrowser() method opens a default browser in KDE to load the google mail url. The GMonitor also sets up a timer to fetch the feed in 60 second interval. The fetchFeed() method uses the KIO framework in KDE to download the content from a URL and parseFeed() parses the downloaded feed and emits a 'mailcount' signal.

The implementation depends on feedparser which can be installed on Ubuntu by running:
$ sudo aptitude install python-feedparser
You can also download and put the file inside the code directory.

Not that bad. It's actually possible to create a very simple 'good looking' Gmail monitor in less than 100 lines of code (excluding comments) with Python and KDE.

To view this plasmoid without installing it run (while standing in the gmonitor folder):
$ make view
This might only work on KDE4.3, not sure if the plasmoidviewer in 4.2 supports running plasmoids without first installing them. If it fails you should install the plasmoid and run plasmoidviewer yourself (or modify the makefile):
$ make install
$ plasmoidviewer pysnippet-gmonitor
If you never heard of Qt signals and slots you should read this introduction on the topic. For example, a button can 'emit' a signal when it's clicked. A slot (function/method) can be connected to a signal and each time the signal is emitted the function/method will be called.

You can find the Python KDE4.3 API docs here. Unfortunately, I don't find them as good as the Qt docs.

When running the applet, KDE will ask for the username/password when it tries to connect to Google. You can check the 'remember the password' checkbox which will make KDE cache the password as long as the desktop session is alive. If you choose not to, you'll have to enter your username/password each time the code tries to fetch the feed. A better solution is to use KWallet.

Ok, hope you enjoyed it and start doing cool plasmoids!

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