molecule | Build a StateFlow stream using Jetpack Compose | Reactive Programming library
kandi X-RAY | molecule Summary
kandi X-RAY | molecule Summary
Jetpack Compose UI makes it easy to build declarative UI with logic. Unfortunately, we are mixing business logic with display logic which makes testing harder than if it were separated. The display layer is also interacting directly with the storage layer which creates undesirable coupling. Additionally, if we want to power a different display with the same logic (potentially on another platform) we cannot. Extracting the business logic to a presenter-like object fixes these three things. In Cash App our presenter objects traditionally expose a single stream of display models through Kotlin coroutine's Flow or RxJava Observable. This code is okay, but the ceremony of combining reactive streams will scale non-linearly. This means the more sources of data which are used and the more complex the logic the harder to understand the reactive code becomes. Despite emitting the Loading state synchronously, Compose UI requires an initial value be specified for all Flow or Observable usage. This is a layering violation as the view layer is not in the position to dictate a reasonable default since the presenter layer controls the model object. Molecule lets us fix both of these problems. Our presenter can return a StateFlow whose initial state can be read synchronously at the view layer by Compose UI. And by using Compose we also can build our model objects using imperative code built on features of the Kotlin language rather than reactive code consisting of RxJava library APIs. This model-producing composable function can be run with launchMolecule. At the view-layer, consuming the StateFlow of our model objects becomes trivial. For more information see the launchMolecule documentation.
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Copypublic void setMass(double mass) {
this.mass = mass;
} Community Discussions
Trending Discussions on Reactive Programming
QUESTION
How can we divide work of consumers over a limited set of resources in RXJS?
I have a Pool class here (simplified):
ANSWER
Answered 2022-Mar-31 at 12:55So the main thing is you need to share the actual part that does the work, not only the resources.
Here's a solution from me:
https://stackblitz.com/edit/rxjs-yyxjh2?devToolsHeight=100&file=index.ts
QUESTION
There are two observables: the first named activator emits booleans. The second named signaler emits void events. There's a function f() which must be called under the next conditions:
If the last event from activator is true, and event from signaler comes, call f(). Otherwise (the last activator's event is false, or activator has not yet emitted anything), "remember" that signaler sent the event. As soon as activator emits true, call f() and clear "remembered" flag.
Example:
...ANSWER
Answered 2022-Mar-23 at 18:10You need a state machine, but you can contain the state so you aren't leaving the monad... Something like this:
QUESTION
We are using spring webflux (project reactor), as part of the requirement we need to call one API from our server.
For the API call, we need to cache the response. So we are using Mono.cache operator.
It caches the response Mono and the next time the same API call happens, it will get it from the cache. Following is example implementation
ANSWER
Answered 2022-Mar-03 at 14:54You can initialize the Mono in the constructor (assuming it doesn't depend on any request time parameter). Using cache operator will prevent multiple subscriptions to the source.
QUESTION
I would like to combine two observables in such a way that
- I mirror at most 1 value from the source observable (same moment it arrives),
- Then ignore its subsequent values until the notifier observable emits;
- Then, I allow to mirror at most 1 more value from the source;
- After which I again ignore elements until the notifier observable emits
- etc.
Source:
...ANSWER
Answered 2022-Jan-20 at 13:05I believe this is a simple use case of the throttle() operator.
QUESTION
I need to copy date from one source (in parallel) to another with batches.
I did this:
...ANSWER
Answered 2021-Dec-04 at 19:50You need to do your heavy work in individual Publisher-s which will be materialized in flatMap() in parallel. Like this
QUESTION
Context
I started working on a new project and I've decided to move from RxJava to Kotlin Coroutines. I'm using an MVVM clean architecture, meaning that my ViewModels communicate to UseCases classes, and these UseCases classes use one or many Repositories to fetch data from network.
Let me give you an example. Let's say we have a screen that is supposed to show the user profile information. So we have the UserProfileViewModel:
ANSWER
Answered 2021-Dec-06 at 14:53The most obvious problem I see here is that you're using Flow for single values instead of suspend functions.
Coroutines makes the single-value use case much simpler by using suspend functions that return plain values or throw exceptions. You can of course also make them return Result-like classes to encapsulate errors instead of actually using exceptions, but the important part is that with suspend functions you are exposing a seemingly synchronous (thus convenient) API while still benefitting from asynchronous runtime.
In the provided examples you're not subscribing for updates anywhere, all flows actually just give a single element and complete, so there is no real reason to use flows and it complicates the code. It also makes it harder to read for people used to coroutines because it looks like multiple values are coming, and potentially collect being infinite, but it's not the case.
Each time you write flow { emit(x) } it should just be x.
Following the above, you're sometimes using flatMapMerge and in the lambda you create flows with a single element. Unless you're looking for parallelization of the computation, you should simply go for .map { ... } instead. So replace this:
QUESTION
I am trying to create a table (with DT, pls don't use rhandsontable) which has few existing columns, one selectinput column (where each row will have options to choose) and finally another column which will be populated based on what user select from selectinput dropdown for each row.
in my example here, 'Feedback' column is the user dropdown selection column. I am not able to update the 'Score' column which will be based on the selection from 'Feedback' column dropdown.
...ANSWER
Answered 2021-Sep-30 at 14:31I'd suggest using dataTableProxy along with replaceData to realize the desired behaviour. This is faster than re-rendering the datatable.
Furthermore, re-rendering the table seems to be messing around with the bindings of the selectInputs.
Also please note: for this to work I needed to switch to server = TRUE
QUESTION
I'm receiving a request through a rest controller method with an object that I'm then passing to a method in the service layer.
The object in this request contains a list as follows:
...ANSWER
Answered 2021-Oct-18 at 16:21The expected way to do that is to actually use the fromIterable method and provide your List:
QUESTION
The following code attempts to react to one Supply and then, based on the content of some message, change its mind and react to messages from a different Supply. It's an attempt to provide similar behavior to Supply.migrate but with a bit more control.
ANSWER
Answered 2021-Oct-07 at 10:20I tend to consider whenever as the reactive equivalent of for. (It even supports the LAST loop phaser for doing something when the tapped Supply is done, as well as supporting next, last, and redo like an ordinary for loop!) Consider this:
QUESTION
I'm trying to use Combine to do several millions concurrent request through the network. Here is a mock up of the naive approach I'n using:
...ANSWER
Answered 2021-Oct-05 at 15:18The issue appears to be a Combine bug, as pointed out here. Using Publishers.Sequence causes the following operator to accumulate every value sent downstream before proceeding.
A workaround is to type-erase the sequence publisher:
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