Add "Check for updates" feature

[bender86]

1) Check if there is an active internet connection: obviously the first step. What is the simplest way? A ping to the server is sufficient? Which qt4 method should I use?

Just try to connect. If it fails, then there is no active connection.

2b) Which compression method should I use for packaging the updates. In linux it's not a problem, what about windows? I don't want more dependencies other than qt4. Maybe a self extracting package?

Try looking to QByteArray::qCompress and QByteArray::qUncompress.

3b) Which method I have to use for downloading?

You can use QHttp or QFtp.

3c) Where I have to download the files? In a tmp folder, obviously; in linux is /tmp but in windows it can change: which qt4 method gives the current system temp folder?

You can use QTemporaryFile.

4b) In windows: thanks to QApplication::applicationDirPath() I know where the application is installed; and there extract the binary. Where I have to put the data files? In the same directory is ok, or in the user profile subfolder? Which qt4 method gives the current user directory?

User data should be in AppData directory. You can obtain it with SHGetSpecialFolderPath, or with %APPDATA% env variable.