Adapt UseCase#13 - "Exception Handling"

Author: LukasLechnerDev

README.md

@@ -168,7 +168,7 @@ The factorial calculation here is not performed by a single coroutine, but by an
 ### 13. Exception Handling
 
 This use case demonstrates different ways of handling exceptions using `try/catch` and `CoroutineExceptionHandler`. It also demonstrates when you should to use `supervisorScope{}`: In situations when you don't want a failing coroutine to cancel
-its sibling coroutines. In the use case the results of the successful responses are shown even tough one response wasn't successful.
+its sibling coroutines. In one implementation of this use case, the results of the successful responses are shown even tough one response wasn't successful.
 
 [[code](app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/coroutines/usecase13/ExceptionHandlingViewModel.kt)]
 

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/coroutines/usecase13/ExceptionHandlingActivity.kt

@@ -42,9 +42,6 @@ class ExceptionHandlingActivity : BaseActivity() {
         binding.btnShowResultsEvenIfChildCoroutineFailsTryCatch.setOnClickListener {
             viewModel.showResultsEvenIfChildCoroutineFails()
         }
-        binding.btnShowResultsEvenIfChildCoroutineFailsRunCatching.setOnClickListener {
-            viewModel.showResultsEvenIfChildCoroutineFailsRunCatching()
-        }
     }
 
     private fun render(uiState: UiState) {
@@ -97,13 +94,11 @@ class ExceptionHandlingActivity : BaseActivity() {
         btnExceptionTryCatch.isEnabled = true
         btnCoroutineExceptionHandler.isEnabled = true
         btnShowResultsEvenIfChildCoroutineFailsTryCatch.isEnabled = true
-        btnShowResultsEvenIfChildCoroutineFailsRunCatching.isEnabled = true
     }
 
     private fun disableButtons() = with(binding) {
         btnExceptionTryCatch.isEnabled = false
         btnCoroutineExceptionHandler.isEnabled = false
         btnShowResultsEvenIfChildCoroutineFailsTryCatch.isEnabled = false
-        btnShowResultsEvenIfChildCoroutineFailsRunCatching.isEnabled = false
     }
 }

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/coroutines/usecase13/ExceptionHandlingViewModel.kt

@@ -3,10 +3,7 @@ package com.lukaslechner.coroutineusecasesonandroid.usecases.coroutines.usecase1
 import androidx.lifecycle.viewModelScope
 import com.lukaslechner.coroutineusecasesonandroid.base.BaseViewModel
 import com.lukaslechner.coroutineusecasesonandroid.mock.MockApi
-import kotlinx.coroutines.CoroutineExceptionHandler
-import kotlinx.coroutines.async
-import kotlinx.coroutines.launch
-import kotlinx.coroutines.supervisorScope
+import kotlinx.coroutines.*
 import timber.log.Timber
 
 class ExceptionHandlingViewModel(
@@ -37,41 +34,6 @@ class ExceptionHandlingViewModel(
     }
 
     fun showResultsEvenIfChildCoroutineFails() {
-        uiState.value = UiState.Loading
-        viewModelScope.launch {
-
-            supervisorScope {
-                val oreoFeaturesDeferred = async { api.getAndroidVersionFeatures(27) }
-                val pieFeaturesDeferred = async { api.getAndroidVersionFeatures(28) }
-                val android10FeaturesDeferred = async { api.getAndroidVersionFeatures(29) }
-
-                val oreoFeatures = try {
-                    oreoFeaturesDeferred.await()
-                } catch (e: Exception) {
-                    Timber.e("Error loading oreo features")
-                    null
-                }
-
-                val pieFeatures = try {
-                    pieFeaturesDeferred.await()
-                } catch (e: Exception) {
-                    Timber.e("Error loading pie features")
-                    null
-                }
-
-                val android10Features = try {
-                    android10FeaturesDeferred.await()
-                } catch (e: Exception) {
-                    Timber.e("Error loading oreo features")
-                    null
-                }
-                val versionFeatures = listOfNotNull(oreoFeatures, pieFeatures, android10Features)
-                uiState.value = UiState.Success(versionFeatures)
-            }
-        }
-    }
-
-    fun showResultsEvenIfChildCoroutineFailsRunCatching() {
         uiState.value = UiState.Loading
         viewModelScope.launch {
 
@@ -84,14 +46,22 @@ class ExceptionHandlingViewModel(
                     oreoFeaturesDeferred,
                     pieFeaturesDeferred,
                     android10FeaturesDeferred
-                ).mapNotNull { deferred ->
-                    runCatching {
-                        deferred.await()
-                    }.onFailure {
-                        Timber.e("Failure loading features of an Android Version")
-                    }.getOrNull()
+                ).mapNotNull {
+                    try {
+                        it.await()
+                    } catch (exception: Exception) {
+                        // We have to re-throw cancellation exceptions so that
+                        // our Coroutine gets cancelled immediately.
+                        // Otherwise, the CancellationException is ignored
+                        // and the Coroutine keeps running until it reaches the next
+                        // suspension point.
+                        if (exception is CancellationException) {
+                            throw exception
+                        }
+                        Timber.e("Error loading feature data!")
+                        null
+                    }
                 }
-
                 uiState.value = UiState.Success(versionFeatures)
             }
         }