Google Play services Task API: continueWith vs continueWithTask

android, firebase

Solution

The primary difference between continueWith and continueWithTask is one of the generic types of the Continuation you pass to it.

You can think of a Continuation as something that converts some input type to some output type. If you define a `Continuation<IN, OUT>`, where `IN` is the input type passed to its `then` method via a `Task<IN>`, and `OUT` is the type that method returns.

When calling `continueWith`, you pass a `Continuation<IN, OUT>`, and the `then` method is expected to compute and return the `OUT` value given a `Task<IN>` value as input. You might choose to do this if you don't have any blocking work to do for the conversion, such as reducing an integer array to the sum of its elements or counting the number of words in a String.

When calling `continueWithTask`, you pass a `Continuation<IN, Task<OUT>>`, and the `then` method is expected to return a `Task<OUT>` that eventually generates the `OUT` value, given the `IN` value as input. You might choose this if you are able to delegate the conversion work to an existing reusable Task.

Practically speaking, you aren't required to choose one or the other to do your work. It's a matter of preferred style, or if you have a nice `Task` ready to delegate your conversation rather than a `Continuation`. Typically you only use a Continuations if you have a pipeline of conversions to chain together.

The javadoc links here show some examples of Continuations. Also, to learn more, you can read about them in part three of my blog series. To be fair, `continueWithTask` is the only part of the Task API I don't directly discuss anywhere in that series, mostly because conceptually it doesn't differ very much from `continueWith`.

Problem

Original source