02
Nov
10

Android Adapters

I’ve been fooling around with Android for a couple of weeks.Android.. I bought a Motorola Milestone, downloaded the ADT plugin, a few device images and started reading and coding…
I have to admit that the Android Architecture has some ingenious points, one example is the idea of having one process (a Dalvik VM instance) hosting both application activities and also its services but this will be subject for another post (android.os.Looper and Handler are worth mentioning too).
Getting back to the reason for the post…

Android Adapter vs Swing TableModel

Having once used Java Swing Toolkit my first impression when I saw Android SimpleAdapter was that I was seeing a DefaultTableModel sibling but the reality was that I couldn’t be more wrong!
Android Adapters and ListViews are more similar to Java’s c:forEach tag (Yeah, I know… probably you thought I would use a Swing metaphor but I couldn’t think of one) since it does not impose a resulting Widget, it is up to the Adapter getView method to determine which will be the rendered View instance. Swing’s TableModel only determines the content that will be displayed but it can’t redefine the UI component JTable uses. This responsibility on Swing is delegated to JTable getDefaultRenderer method.

Android SimpleAdapter

Android’s SimpleAdapter employs a rather simple yet smart strategy: you handle it Composite component ID that will be displayed for each row of a List of HashMaps. The mapping of each subcomponent from the composite component is performed by two Arrays that are also passed at SimpleAdapter construct time. These arrays maps the Keys from the HashMap into the subcomponent IDs.

SimpleAdapter drawback

What I sincerely miss with the SimpleAdapter approach is a more direct mapping between domain objects and the ListView. The developer ends up coding a plumbing code that moves data from Domain Objects into the HashMap and this code easily violates the DRY principle.
Although reflection poses a performance penalty I’ll try to see if a ReflectionAdapter based on SimpleAdapter is a valid alternative.

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