Before we start designing a database-driven tasklist application, let's first familiarize ourselves with SQLite in the context of a seemingly much simpler set of requirements: storing username/password combinations in a database and refactoring the Logon class to interact with this database.
The functional requirements are deceptively simple: to verify whether a username/password combination is valid, all we have to do is verify that the username/password combination given is present in the table of usernames and passwords. Such a table consists of two columns, one named username and the other named password. As it is never a good idea to store a collection of passwords in plaintext, we encrypt the passwords with a hash function so even if the password database is compromised, the bad guys will have a difficult time retrieving the passwords. This means, of course, that we have to hash a given password with the same hash function before comparing it to the stored...