This lesson describes how you can easily take any expensive method and wrap the call inside an
Once you start using
RxJava, you will want all slow methods to return an
Observable to enable you to use all of the benefits of
RxJava. However, this isn't always possible. Sometimes, you can't change what a method returns, but you still want to use the power of
RxJava. This is a typical problem in working with legacy code.
Observable.fromCallable() 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.fromCallable() 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() can't help us solve this problem.
Summary of Content:
- How to convert a simulated "read database" operation into an
Observable.from()doesn't solve this problem
- How to create an
Observable.fromCallable()lets you wrap an expensive method call
- The expensive method call will only happen when something subscribes
- How to clean up the syntax using Java 8 / Retrolambda
- Example project reading a value from a database with the use of
fromCallable()to do the read in a background thread.