I usually talk about AudioMan's models like they are all one component, but in this post I'll get into what they are all about. The models are one part of the model-view-controller triple that I talked about before and then updated more recently. They contain the data that is displayed in the view that the user can see. The controller takes direction from the GUI and manipulates the contents of the models, like when a user is browsing a collection.

There are four models, one each for the playlists, artists, albums and tracks. The contents of each subsequent model in that order depends on what is selected in the previous model. In that way, they sort of cascade. The playlists model is just a Vector of name/value pairs. The name is the label you see in the view and the value is the playlist's ID number.

The artist list contains a list of all of the artists in the selected playlist. The album list contains a list of all of the albums in the selected playlist and by the selected artist.

Finally, the track list contains all of the tracks that fit the playlist, artist and album that are selected. Like the playlists, it is also just a Vector but of AudioData objects representing tracks.

The artist and album models are the most interesting. They receive add/remove notifications from the tracks mutator just like the tracks model does, in order to add and remove artist and album names on the fly. To do this accurately, these models needed to keep a count of the number of tracks that apply to a specific artist or album name.

So I made the artist and album models Hashtables. The key in the Hashtable is the artist or album name and the value is the number of tracks that use that name. When these models receive an add notification from the tracks mutator, if the name isn't in the list it's added to the Hashtable with a value of 1. It it is in the list, the value is incremented. When these models receive an remove notification from the tracks mutator, if the name is in the list but the value is only 1 then the name is removed. Otherwise if the entry exists the count is decremented.

How does a model know if it should listen to a notification from a mutator? It can't listen to them all because some additions and removals don't apply to what it's showing. That's where the TrackFilter object comes in and I'll explain that one in another post.