#Positronic Net

Positronic Net is an attempt to reduce the amount of boilerplate coding required for Android programming to just connect framework components together. It's written in Scala, and uses Scala features (traits, a/k/a mixins, and functional arguments) to let programmers say what they mean without so much chatter about components of the framework itself.

It builds using sbt version 0.7.7 and the sbt-android-plugin.

The project source includes the library itself (in src) and a simple sample app (as an sbt subproject); reading the sample app code might be the best way to get a feel for what the library is trying to accomplish.

#Features

What's in the package right now includes the following:

##Event handler declarations in a style reminiscent of jQuery:

listsView.onItemClick { (view, posn, id) => viewListAt( posn ) }

findView( TR.addButton ).onClick { doAdd }
findView( TR.newListName ).onKey( KeyEvent.KEYCODE_ENTER ){ doAdd }

onOptionsItemSelected( R.id.undelete ) { doUndelete }

These come from a PositronicHandler trait and friends, which come premixed into PositronicActivity, PositronicButton, and so forth. (These extend the corresponding Android platform classes, so if you don't have a Positronic shorthand for something, or just don't like it, the standard API is fully available.)

##Fluid notation for dealing with Sqlite

A sample, implementing a soft deletion scheme:

val dbItemsAll = TodoDb("todo_items").whereEq("todo_list_id"->id)
val dbItems    = dbItemsAll.whereEq( "is_deleted" -> false )

// ... and later ...

def deleteWhereDone = {
  dbItemsAll.whereEq( "is_deleted" -> true ).delete // purge the last batch
  dbItems.whereEq( "is_done" -> true ).update( "is_deleted" -> true )
}

##"Change listener" framework

It's generally good practice on Android to manipulate databases, and perform other background operations, on a thread different from the one that runs the user interface. But it can be a pain to arrange. Positronic Net includes a CursorSourceAdapter class which can be used like so:

class TodosAdapter( activity: PositronicActivity )
 extends CursorSourceAdapter( activity, 
                              source = TodoLists.lists,
                              converter = TodoList.fromCursor(_),
                              itemViewResourceId = R.layout.todos_row )
{
  def bindItem( view: View, list: TodoList ) =
    view.asInstanceOf[ TextView ].setText( list.name )
}

You use this by instantiating it and calling listView.setAdapter(...), as with any other adapter. The difference is that this one arranges with the cursor source (actually a ChangeNotifications[Cursor]) to hear about updates to the underlying data, within the lifetime of its enclosing activity. (It stops listening when the activity is destroyed.) When changes occur, the attached view gets updated, on the activity's UI thread.

This is an attempt to meet the same basic need as the CursorLoader machinery in Android 3.0, but with better encapsulation and less chatter.

##Miscellaneous shorthands

The library also provides alternate overloads for a lot of standard framework APIs (usually to give them functional arguments instead of, say, a Runnable), which allow common usage patterns to be more clearly (and briefly) expressed. I've also tried to cut down on other forms of chatter --- if you always have to call super.foo(), the Positronic Net alternate version of foo will often do that for you. (Again, if you're doing something unusual, the standard APIs and entrypoints are always available.)