Hi fellow Android coders,
that’s a problem I struggle with every time when I make a new app. Imagine you have sub classes of Activity, ListActivity and MapActivity in your app. Now I want that every screen has the same options menu showing up when the user clicks the menu button. So I made a BaseActivity with that behavior. But because Java doesn’t allow multiple inheritance I have to write three BaseActivities for every type of Activity. That is ugly because I have three times the same code… The only solution I can think of is make some of the behavior static in one of those BaseActivities and refer to that in the other BaseActivites. But there are still a lot of duplicates… Anyone has a more elegant solution for that problem?
Cheers
This is one of the trade-offs for a single-inheritance language. Rather than duplicating code through inheriting various Activity sub-classes use a delegate. This is also called inheritance by delegation. You will get the features of multiple inheritance without the liabilities.
This is a accomplished by creating a delegate class that has all the shared functionality you’d like then having the “super” class call the delegate. This will still require a small level of copy-and-paste code but it will be minimal. Wikipedia has a good example of the Delegation pattern. If you have a background in C# this form of delegation is similar but not restricted to single methods and for more than events.