Android LiveData Resource: Propagate Data or Exception (Kotlin)
August 19, 2019Use a Resource
object to hold data or exception.
class Resource<out T> private constructor(
private val data: T?,
private val error: Throwable?
) {
val isSuccessful: Boolean
get() = data != null && error == null
constructor(data: T) : this(data, null)
constructor(exception: Throwable) : this(null, exception)
fun data(): T {
if (error != null) {
throw IllegalStateException("Check isSuccessful first: call error() instead.")
}
return data!!
}
fun error(): Throwable {
if (data != null) {
throw IllegalStateException("Check isSuccessful first: call data() instead.")
}
return error!!
}
}
NOTE: Alternative Resource object solution
Usage
val messageLiveData = MutableLiveData<Resource<String>>()
fun getMessage() {
try {
// fetch data
val message = ...
messageLiveData.value = Resource(message)
}
catch (e: Exception) {
messageLiveData.value = Resource(e)
}
}
messageLiveData.observe(lifecycleOwner, Observer { event ->
if (event.isSuccessful) {
val message = res.data()
// do something
}
else {
val e = res.error()
// handle exception
}
}
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