Find out how to Create a State Machine on Jetpack Compose | by Marco Cattaneo | Solo Tech

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Let’s have a look at how you can create a State Machine and implement it in Jetpack Compose

Why do we want a state machine in Jetpack Compose? Let’s begin with the fundamentals!

jetpack compose

Jetpack Compose is the brand new framework launched by Google that can substitute the present XML view system launched a a decade in the past. It is rather completely different from the earlier one as a result of we’re transferring from the Crucial Programming strategy to Declarative Programming, the place the person interface parts are capabilities and every argument represents a property or perhaps a situation of our element.

The state: that is a very powerful a part of this text as a result of principally Compose was designed to react to a change of statebecause of this our major aim is to seek out one of the best ways to control this situation.

Once I say “higher” I imply:

  • retaining this state constant throughout execution
  • make code readable/maintainable with out spaghetti code 🍝
  • making it testable (please do not skip this level 😈)

Case research

The aim of this text is to clarify how you can implement a State Machine utilizing this library, how you can combine it with Jetpack Compose, and final however not least, how you can write exams on it.

Our case research can be a small software that permits the person to sort in a Github username and get the checklist of associated repositories, so our area layer will expose this interface:

In any other case, from the person interface standpoint, our software can be composed of a Textual content subjecta affirmation Button and a lazy column, like this snippet:

Now we have to discover a higher glue for the person interface and the area layer: a stage machine. My suggestion is to begin excited about states, what set of states will my UI render? I’ve considered three of them:

  • content material standing: the place principally the Textual content subject is valued with the username and the lazy column with the checklist of repositories (LazyColumn works as a RecyclerView)
  • State of cost: used when the applying makes the HTTP request
  • Error state: is the case one thing goes mistaken

Now occasions/actions that may manipulate our state:

  • The person is typing the username.: in composing there’s the idea of one-way information circulate (learn extra right here), so we should persist within the Textual content subject‘s worth inside our state.
  • Verify button pressed: the occasion fires when a person faucets the search button.
  • The person requests a retry: activated by the retry button on the error standing.

If we draw the state machine it ought to look one thing like this:

Software state machine

From a code standpoint, these may very well be our state Y Behaviour:

States and actions

the state machine

Now for the enjoyable half, we’re going to implement the state machine and we have to outline the supported actions for every of those states. Redux Circulate will assist us on this iteration.

Redux Circulate is a library that permits you to create a state machine the place for every state we are able to declare (in DSL trend) which actions are supported. Every motion is able to doing logic and manipulating state in numerous methods:

  • cancel the state with a brand new one
  • transfer state properties with out altering the sort
  • maintain the identical state with out adjustments

Try the pattern under.

Principally, we’re making a FlowReduxStateMachine with a state primarily based on GithubState and a set of actions primarily based on the GithubAction, then we now have to outline the preliminary state, which goes to be the preliminary state, in our case it’s the ContentState (the place enter and repositories are empty).

Now we have to describe the habits of the State Machine contained in the Specs , Redux Circulate permits you to outline completely different behaviors for any motion primarily based on the present state.

From the Content material Standing:

On this state, we are saying that every time the UI points:

  • GithubAction.TypeOwner we mutate the ContentState to persist person enter.
  • GithubAction.Commit we canceled it with state of cost which comprises the username typed by the person (if not empty, in any other case we do nothing).
ContentState Actions

And the Burden situation?

It is a bit of completely different as a result of we’re utilizing the on Enter operate, this operate known as each time the state transits to Burdenand that is excellent as a result of we are able to name the Github repository and get the checklist of repositories.

Load actions and error states

In case we’re profitable, we override the state with the ContentState in any other case, we change to a Mistake state, the place we are able to principally retry the decision:

Find out how to combine StateMachine into Jetpack Compose

The state machine is prepared, now we have to connect it to our composable UI. There are various choices, I’ve determined to encapsulate the state machine inside a view mannequin and cross it to the UI.

Principally, I’ve a abstract AbsStateViewModel that exposes the state and permits the issuance of the shares utilizing the viewModelScope (as a result of the workplace technique of FlowReduxStateMachine it is a sleep operate).

so i created a GithubViewModel which extends this class:

And eventually, I can cross the See mannequin contained in the Composable operate, that is the consequence:


Hears! The place are you going? Now your state machine is prepared however you additionally want to jot down exams! It is fairly easy, since standing updates journey in a Kotlin Circulate you want a library that can assist you check solid, i counsel which inserts our scopes.

I’ve additionally used for mocking and in case you are I additionally wrote an article about it.

On this check, for instance, we’re testing the typing of the username:

I am testing writing

on this one, we’re testing the habits in case the API name fails:

I am testing search on failure.


Redux Circulate it is a cool library, is it one of the best answer? Possibly sure or perhaps no, we love the “relies upon” prayer, up to now I additionally labored a bit of with IM V sample, and my feeling is that it really works just about the identical means however we now have extra management as a result of we are able to simply outline which actions can be found for a particular state and so they have a greater hierarchy. One other professional is said to the declaration, the DSL syntax simplifies the code and makes it extra readable and maintainable.

I hope you loved studying this text! Please go away 1/2/tons of 👏 if you happen to preferred it, feedback are welcome too!

I hope the article not fairly Find out how to Create a State Machine on Jetpack Compose | by Marco Cattaneo provides acuteness to you and is beneficial for toting as much as your information

How to Create a State Machine on Jetpack Compose | by Marco Cattaneo