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@quentin41500
Last active June 8, 2021 12:28
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Using Sealed class and LiveData to handle network request through the repository layer.
/**
* Observable manager for saving the [Cart]'s resource information.
*/
class CartManager : LiveData<Resource<Cart?>>() {
init {
value = Success(null)
}
/**
* Set the [Cart] value and notifies observers.
*/
internal fun set(cart: Cart) {
postValue(Success(cart))
}
/**
* Clear any information from the device.
*/
internal fun clear() {
postValue(Success(null))
}
/**
* Signals that the resource information is being retrieved from network.
*/
internal fun loading() {
postValue(Loading())
}
/**
* Signals that an error occurred when trying to fetch the resource information.
*/
internal fun error(t: Throwable) {
postValue(Failure(t))
}
}
/**
* [Cart] repository class in charge of providing api for getting and updating a [Cart] data.
*/
class CartRepository(private val service: RetrofitApi, private val cartManager: CartManager) {
fun getCartResource(): LiveData<Resource<Cart?>> = cartManager
/**
* Get a [Cart].
*/
suspend fun get() {
withContext(Dispatchers.IO) {
try {
cartManager.loading()
val cart = service.getCart().await()
cartManager.set(cart)
} catch (e: Exception) {
cartManager.error(e)
}
}
}
/**
* Add a [Cart] shipping information.
*/
suspend fun addShippingAddress(shipping: ShippingAddress) {
withContext(Dispatchers.IO) {
try {
cartManager.loading()
val cart = service.addShippingAddress(shipping).await()
cartManager.set(cart)
} catch (e: Exception) {
cartManager.error(e)
}
}
}
}
class CheckoutActivity : AppCompatActivity() {
private lateinit var vm: CheckoutViewModel
override fun onCreate(savedInstanceState: Bundle?) {
// Initialization
...
vm.cart.observe(this, Observer { resource ->
when (resource) {
is Loading -> showLoading()
is Success -> {
displayCart(resource.data) // Do something with your data.
hideLoading()
}
is Failure -> {
showError(resource.throwable) // Do something with your error.
hideLoading()
}
})
}
}
class CheckoutViewModel(repo: CartRepository) : ViewModel() {
/**
* Live data for [Cart] information.
*/
val cart: LiveData<Resource<Cart?>> = repo.getCartResource()
}
/**
* Represents a network bound resource. Each subclass represents the resource's state:
* - [Loading]: the resource is being retrieved from network.
* - [Success]: the resource has been retrieved (available in [Success.data] field)
* - [Failure]: the resource retrieving has failed (throwable available in [Failure.throwable] field)
*/
sealed class Resource<out T> {
class Loading<out T> : Resource<T>()
data class Success<out T>(val data: T) : Resource<T>()
data class Failure<out T>(val throwable: Throwable) : Resource<T>()
}
@iRYO400
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iRYO400 commented Jun 4, 2019

Hello! I've read your article. This implementation is exactrly what I looked for. But due to my experience, I dont understand what resource is in CartManager:

...
resource = Success(null)
...
resource = Loading()
...
resource = Failure(t)
...

Thanks!

@quentin41500
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Author

I originally was using a variable but realized later I didn't need it. You can just pass the created objects to live data right away.
postValue(Success(null))

I will make the edit.

@aalap03
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aalap03 commented Feb 17, 2020

What if we use a boolean in loading so we have to just pass boolean on completion once, and not twice at both error and success case ?

@whoyawn
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whoyawn commented Sep 1, 2020

What if you're integrating a database layer? Would we still be observing the resource in the UI if you want to fetched cached objects?

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