CODEWITHSUNDEEP
javaandroidmodel-view-controllerobserver-pattern
Trevor
Trevor

Reputation: 10993

Android: Using observer pattern with Views (possibly MVC, MVVM related)

I've spent some hours reading various questions and answers regarding implementing the various MVC-type patterns in Android. I've seen a few code examples posted in various blogs. I would, however, still appreciate some ideas and opinions on what I am trying to achieve. Specifically, I'd like to work out the best code mechanism to inform a single View, or a group of Views, that a particular item of data has been changed.

My application is quite simply one which obtains measurement data from a hardware device via Bluetooth, and displays and logs that data. At present, I have a Service which takes care of Bluetooth communications and background logging. I have a 'global' data store class that is an extension of Application.

As measurement data is polled from the external device, the measurement data (which is in reality about thirty bytes of data) is updated in the data store object (which, in MVC terms, I'm guessing is the 'model').

At any time, only a small subset of that data will be displayed by UI Views. Typically, a given View will only be interested in representing one particular byte of measurement data. As the user moves to different Activity classes, other Views will be displayed which would display a different subset of that data.

So to get to the point, I'm trying to choose the best way to cause invalidate() to be invoked on interested Views when a given data item is changed.

The options seem to be:

  1. Make use of the existing Observer class, and related classes.

  2. Kind of 'roll my own' observer pattern, by creating my own register() and unregister() functions in the data model. Observer Views would be held in an ArrayList (or perhaps a more complex arrangement of one observer List per data item). I'd loop through this ArrayList each time data are updated and call invalidate() (or postInvalidate() of course, depending on my threading arrangement).

Are there any reasons why I should use one of the above over the other? And is there any other 'observer' mechanism I should consider?

Upvotes: 4

Views: 4566

Answers (2)

Brook Oldre
Brook Oldre

Reputation: 21

Another Option would be to use the Android Intent framework. When new data is received in the service set the data to the universal model and broadcast an intent that the data has been updated using the Context.broadcastIntent(Intent) method. Any view that is interested in that data would register and unregister receivers using the Context.RegisterReceiver(Receiver) and Context.unregisterReceiver(Receiver) methods. From there the view would retrieve the data from the universal model and update the view accordingly.

I think this might be what the observer pattern in Android.Lifecycle.Observer package is doing behind the scenes.

Upvotes: 0

dontocsata
dontocsata

Reputation: 3071

Many views in Android are backed by some subclass of BaseAdapter which has a method notifyDataSetChanged() which instructs the view to refresh itself. If you are using a view (such as ListView or GridView or any descendent of AdapterView) then it is backed by a BaseAdapter and you can simply update that Adapter and the view will refresh itself.

I guess this means, I vote that you use the built-in observer pattern. If you are using a custom view then obviously this won't work and you would have to use a custom method of refreshing anyway.

Upvotes: 3

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