metalabdesign/ AsyncAwait

(1.0.0) over 4 years ago

Kotlin

Java

Shell

coroutines

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metalabdesign

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Apache License 2.0

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Description

async/await for Android built upon coroutines introduced in Kotlin 1.1

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Async/Await

Name: AsyncAwait
Brand: AsyncAwait
SKU: //metalabdesign/AsyncAwait
Rating: 2.775 (410 reviews)

A Kotlin library for Android to write asynchronous code in a simpler and more reliable way using

async

await

approach, like:

async {
   progressBar.visibility = View.VISIBLE
   // Release main thread and wait until text is loaded in background thread
   val loadedText = await { loadFromServer() }
   // Loaded successfully, come back in UI thread and show the result
   txtResult.text = loadedText
   progressBar.visibility = View.INVISIBLE
}

As you see in the example above, you can write asynchronous code in a imperative style, step by step. Calling

await

to run code in background doesn't lock the UI thread. And execution continues in UI thread after background work is finished. There is no magic, see how it works.

Dependency

compile 'co.metalab.asyncawait:asyncawait:1.0.0'

Usage

async

Coroutine code has to be passed as a lambda in

async

function

Kotlin
async {
   // Coroutine body
}

await

Long running code has to be passed as a lambda in

await

function

Kotlin
async {
   val result = await {
      //Long running code
   }
   // Use result
}

You may have many

await

calls inside

async

block, or have

await

in a loop

async {
   val repos = await { github.getRepos() }
   showList(repos)
   repos.forEach { repo ->
      val stats = await { github.getStats(repo.name) }
      showStats(repo, stats)
   }
}

awaitWithProgress

Use it to show loading progress, its second parameter is a progress handler.

Kotlin
val loadedText = awaitWithProgress(::loadTextWithProgress) {
         // Called in UI thread
         progressBar.progress = it
         progressBar.max = 100
      }

A data loading function (like the

loadTextWithProgress

above) should have a functional parameter of type

(P) -> Unit

which can be called in order to push progress value. For example, it could be like:

Kotlin
private fun loadTextWithProgress(handleProgress: (Int) -> Unit): String {
   for (i in 1..10) {
      handleProgress(i * 100 / 10) // in %
      Thread.sleep(300)
   }
   return "Loaded Text"
}

Handle exceptions using

try/catch

async {
   try {
      val loadedText = await {
         // throw exception in background thread
      }
      // Process loaded text
   } catch (e: Exception) {
      // Handle exception in UI thread
   }
}

Handle exceptions in

onError

block

Could be more convenient, as resulting code has fewer indents.

onError

called only if exception hasn't been handled in

try/catch

Kotlin
async {
   val loadedText = await {
      // throw exception in background thread
   }
   // Process loaded text
}.onError {
   // Handle exception in UI thread
}

Unhandled exceptions and exception delivered in

onError

wrapped by

AsyncException

with convenient stack trace to the place where

await

been called originally in UI thread

finally

execution

finally

always executed after calling

onError

or when the coroutine finished successfully.

Kotlin
async {
   // Show progress
   await { }
}.onError {
   // Handle exception
}.finally {
   // Hide progress
}

Safe execution

The library has

Activity.async

and

Fragment.async

extension functions to produce more safe code. So when using

async

inside Activity/Fragment, coroutine won't be resumed if

Activity

is in finishing state or

Fragment

is detached.

Avoid memory leaks

Long running background code referencing any view/context may produce memory leaks. To avoid such memory leaks, call

async.cancelAll()

when all running coroutines referencing current object should be interrupted, like

Kotlin
override fun onDestroy() {
      super.onDestroy()
      async.cancelAll()
}

The

async

is an extension property for

Any

type. So calling

[this.]async.cancelAll

intrerrupts only coroutines started by

[this.]async {}

function.

Common extensions

The library has a convenient API to work with Retrofit and rxJava.

Retorift

```
awaitSuccessful(retrofit2.Call)
```

Returns

Response.body()

if successful, or throws

RetrofitHttpError

with error response otherwise.

Kotlin
async {
   reposList = awaitSuccessful(github.listRepos(userName))
}

rxJava

await(Observable)

Waits until

observable

emits first value.

Kotlin
async {
   val observable = Observable.just("O")
   result = await(observable)
}

How to create custom extensions

You can create your own

await

implementations. Here is example of rxJava extension to give you idea. Just return the result of calling

AsyncController.await

with your own lambda implementation. The code inside

await

block will be run on a background thread.

Kotlin
suspend fun  AsyncController.await(observable: Observable): V = this.await {
   observable.toBlocking().first()
}

How it works

The library is built upon coroutines introduced in Kotlin 1.1.

The Kotlin compiler responsibility is to convert coroutine (everything inside

async

block) into a state machine, where every

await

call is a non-blocking suspension point. The library is responsible for thread handling, error handling and managing state machine. When background computation is done the library delivers result back into UI thread and resumes coroutine execution.