Description

This lesson describes how you can easily take any expensive method and wrap the call inside an RxJava Observable using the defer() operator.

We describe Observable.defer() and how we can use this to wrap any method in an Observable so that we can defer the execution of an expensive method until the correct time, and so that we can control which threads are used to execute the method.

We provide an example project where we use Observable.defer() and Observable.just() together to execute a slow method on a background thread and return the result on the Android main thread.

We describe why simply using Observable.just() on its own can't help us solve this problem.

Summary of Content:

• Description of problem; how to convert a long running operation into an RxJava Observable using defer
• How to convert a simulated "read database" operation into an Observable
• How to create an Observable using defer()
• defer() lets you wrap an expensive method call
• The expensive method call will only happen when something subscribes
• Example project reading a value from a database, done with the use of defer(), to do the read in a background thread.
• How to handle exceptions when using defer

Code Links:

• https://github.com/CDRussell/CasterRxJava/tree/defer

Other Relevant Links:

• http://reactivex.io/documentation/operators/defer.html