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POShould I use a listener interface or handler for event callbacks in Android development?
 

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  1. POShould I use a listener interface or handler for event callbacks in Android development?
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    <p>I'm new to Java, I'm porting over our Windows Phone 7 library to run on Android. Due to syntax similarities this has been very simple so far. Our library is basically an abstracted http message queue that provides data persistence and integrity on mobile platforms. It only provides asynchronous methods which is a design choice. On WP7 I make use of delegates to call the user supplied callback when an async message has been processed and the servers response received. </p> <p>To achieve the same thing on Android I've found two ways so far - A simple Java listener interface that contains OnSuccess and OnFailure methods that the user must implement, or using the Android handler class which provides a message queue between threads (http://developer.android.com/reference/android/os/Handler.html). </p> <p>I've gone with the Handler at this stage as if I'm honest it is the most similar to a C# delegate. It also seems like less work for a user of our library to implement. Example of some user code to make use of our library:</p> <pre><code>connection.GetMessage("http://somerestservice.com", GetCallback); Handler GetCallback = new Handler() { public void handleMessage(Message message){ CustomMessageClass customMessage = (CustomMessageClass)message.obj; if(customMessage.status == Status.Delivered) { // Process message here, // it contains various information about the transaction // as well as a tag that can contain a user object etc. // It also contains the servers response as a string and as a byte array. } } }; </code></pre> <p>Using this the user can create as many different handlers as they'd like, called whatever they'd like, and pass them in as method parameters. Very similar to a delegate...</p> <p>The reason I'm wondering if I should move to a listener interface is because the more exposure I gain to Java the more it seems that's just how it's done and it's how third parties using our library would expect it to be done. </p> <p>It's essentially the same process, except each time you wanted to do something different with the server response i.e. You might be fetching different types of data from different endpoints, you're going to have to create a custom class that implements our interface each time, as well as implementing any methods our interface has. Or of course you could have a single monolithic class that all server responses were funneled in to but have fun trying to figure out what to do with each individual response...</p> <p>I may be a bit biased due to coming from C# but a listener seems a bit convoluted and I like the handler implementation better, do any Java developers have any thoughts/advice? It would be much appreciated.</p> <p>Cheers!</p>
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    1. COI'm new to Java and Android myself, so I'm not qualified to answer fully, but my understanding is that the definitions of listener and handler are a bit blurry, especially across platforms. In the Android Dev Guide, in the [UI event section](http://developer.android.com/guide/topics/ui/ui-events.html), they describe listeners as objects that you bind to particular events on your view. You do this externally without necessarily extending the view object. Whereas they describe handlers as standard methods of the View class that you override when you extend it.
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