Again I received a mail from somebody who asked for lists with forward/backward paging option. These lists are not trivial to implement but I was more intrigued by the need why anyone would want such a clumsy UI construct. Then it turned out that the guy wanted to back the list with data from a web service. Obviously, he did not want to wait until the entire list is loaded through the network but wanted to present something to the user as soon as possible.

Such a list can be found in Android Market when the list of applications is progressively loaded from the network server. The problem is worth a simple test program to analyse because it clearly shows the power of the Android adapter concept.

Click here to download the test program.

I got another question whether TableLayout can be used like a two-dimensional ListView. My initial reaction was that it cannot be done because TableLayout just arranges items, all the complicated focusing/highlighting logic in ListView is completely missing from TableLayout. I realized later on, however, that TableLayout can contain Buttons and the rest will be arranged by the general focus handling logic in ViewGroup.

Click here to download the example program.

The only exciting part of this rather simple program is the way how an array of Buttons are made to look like selectable list items. The key is that the Buttons are styled. For example (XML fragments are mangled due to blog engine limitations):
 

I got another trivial question in a comment: how to add checkboxes to an expandable list view like this one? Nothing can be simpler, you just add CheckBox control to the child view that forms the row and that's it. Except that it does not work without some tweaks.

You can download the example program from here.

Service API changes starting with Android 2.0

Watching developers use the Android platform the last year has shown a number of trouble areas in the Service API as well as growing issues in the ways services operate. As a result, Android 2.0 introduced a number of changes and improvements in this area for both developers and users.

The three main changes to be aware of are:

• Service.setForeground() is now deprecated and in 2.0 does nothing.
• There were many edge cases in the service lifecycle that made it very easy to accidentally leave a service running; new APIs in 2.0 make this much easier to deal with.
• Android 2.0 also introduces a new UI for end users to monitor and manage the running services on their device.

A RatingBar is an extension of SeekBar and ProgressBar that shows a rating in stars. The user can touch/drag or use arrow keys to set the rating when using the default size RatingBar. The smaller RatingBar style ( ratingBarStyleSmall) and the larger indicator-only style (ratingBarStyleIndicator) do not support user interaction and should only be used as indicators.