Remove Result, add exceptions

app/src/main/java/com/example/android/architecture/blueprints/todoapp/addedittask/AddEditTaskViewModel.kt

@@ -21,7 +21,6 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import com.example.android.architecture.blueprints.todoapp.R
 import com.example.android.architecture.blueprints.todoapp.TodoDestinationsArgs
-import com.example.android.architecture.blueprints.todoapp.data.Result.Success
 import com.example.android.architecture.blueprints.todoapp.data.Task
 import com.example.android.architecture.blueprints.todoapp.data.source.TasksRepository
 import dagger.hilt.android.lifecycle.HiltViewModel
@@ -132,9 +131,8 @@ class AddEditTaskViewModel @Inject constructor(
             it.copy(isLoading = true)
         }
         viewModelScope.launch {
-            tasksRepository.getTask(taskId).let { result ->
-                if (result is Success) {
-                    val task = result.data
+            tasksRepository.getTask(taskId).let { task ->
+                if (task != null) {
                     _uiState.update {
                         it.copy(
                             title = task.title,

app/src/main/java/com/example/android/architecture/blueprints/todoapp/data/source/DefaultTasksRepository.kt

@@ -16,8 +16,6 @@
 
 package com.example.android.architecture.blueprints.todoapp.data.source
 
-import com.example.android.architecture.blueprints.todoapp.data.Result
-import com.example.android.architecture.blueprints.todoapp.data.Result.Success
 import com.example.android.architecture.blueprints.todoapp.data.Task
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.Dispatchers
@@ -35,13 +33,9 @@ class DefaultTasksRepository(
     private val ioDispatcher: CoroutineDispatcher = Dispatchers.IO
 ) : TasksRepository {
 
-    override suspend fun getTasks(forceUpdate: Boolean): Result<List<Task>> {
+    override suspend fun getTasks(forceUpdate: Boolean): List<Task> {
         if (forceUpdate) {
-            try {
-                updateTasksFromRemoteDataSource()
-            } catch (ex: Exception) {
-                return Result.Error(ex)
-            }
+            updateTasksFromRemoteDataSource()
         }
         return tasksLocalDataSource.getTasks()
     }
@@ -50,7 +44,7 @@ class DefaultTasksRepository(
         updateTasksFromRemoteDataSource()
     }
 
-    override fun getTasksStream(): Flow<Result<List<Task>>> {
+    override fun getTasksStream(): Flow<List<Task>> {
         return tasksLocalDataSource.getTasksStream()
     }
 
@@ -61,33 +55,35 @@ class DefaultTasksRepository(
     private suspend fun updateTasksFromRemoteDataSource() {
         val remoteTasks = tasksRemoteDataSource.getTasks()
 
-        if (remoteTasks is Success) {
-            // Real apps might want to do a proper sync, deleting, modifying or adding each task.
-            tasksLocalDataSource.deleteAllTasks()
-            remoteTasks.data.forEach { task ->
-                tasksLocalDataSource.saveTask(task)
-            }
-        } else if (remoteTasks is Result.Error) {
-            throw remoteTasks.exception
+        // Real apps might want to do a proper sync, deleting, modifying or adding each task.
+        tasksLocalDataSource.deleteAllTasks()
+        remoteTasks.forEach { task ->
+            tasksLocalDataSource.saveTask(task)
         }
     }
 
-    override fun getTaskStream(taskId: String): Flow<Result<Task>> {
+    override fun getTaskStream(taskId: String): Flow<Task?> {
         return tasksLocalDataSource.getTaskStream(taskId)
     }
 
     private suspend fun updateTaskFromRemoteDataSource(taskId: String) {
         val remoteTask = tasksRemoteDataSource.getTask(taskId)
 
-        if (remoteTask is Success) {
-            tasksLocalDataSource.saveTask(remoteTask.data)
+        if (remoteTask == null) {
+            tasksLocalDataSource.deleteTask(taskId)
+        } else {
+            tasksLocalDataSource.saveTask(remoteTask)
         }
     }
 
     /**
-     * Relies on [getTasks] to fetch data and picks the task with the same ID.
+     * Relies on [getTasks] to fetch data and picks the task with the same ID. Will return a null
+     * Task if the task cannot be found.
+     *
+     * @param taskId - The ID of the task
+     * @param forceUpdate - true if the task should be updated from the remote data source.
      */
-    override suspend fun getTask(taskId: String, forceUpdate: Boolean): Result<Task> {
+    override suspend fun getTask(taskId: String, forceUpdate: Boolean): Task? {
         if (forceUpdate) {
             updateTaskFromRemoteDataSource(taskId)
         }
@@ -110,9 +106,7 @@ class DefaultTasksRepository(
 
     override suspend fun completeTask(taskId: String) {
         withContext(ioDispatcher) {
-            (getTaskWithId(taskId) as? Success)?.let { it ->
-                completeTask(it.data)
-            }
+            getTaskWithId(taskId)?.run { completeTask(this) }
         }
     }
 
@@ -125,9 +119,7 @@ class DefaultTasksRepository(
 
     override suspend fun activateTask(taskId: String) {
         withContext(ioDispatcher) {
-            (getTaskWithId(taskId) as? Success)?.let { it ->
-                activateTask(it.data)
-            }
+            getTaskWithId(taskId)?.run { activateTask(this) }
         }
     }
 
@@ -154,7 +146,7 @@ class DefaultTasksRepository(
         }
     }
 
-    private suspend fun getTaskWithId(id: String): Result<Task> {
+    private suspend fun getTaskWithId(id: String): Task? {
         return tasksLocalDataSource.getTask(id)
     }
 }

app/src/main/java/com/example/android/architecture/blueprints/todoapp/data/source/TasksDataSource.kt

@@ -16,7 +16,6 @@
 
 package com.example.android.architecture.blueprints.todoapp.data.source
 
-import com.example.android.architecture.blueprints.todoapp.data.Result
 import com.example.android.architecture.blueprints.todoapp.data.Task
 import kotlinx.coroutines.flow.Flow
 
@@ -25,15 +24,15 @@ import kotlinx.coroutines.flow.Flow
  */
 interface TasksDataSource {
 
-    fun getTasksStream(): Flow<Result<List<Task>>>
+    fun getTasksStream(): Flow<List<Task>>
 
-    suspend fun getTasks(): Result<List<Task>>
+    suspend fun getTasks(): List<Task>
 
     suspend fun refreshTasks()
 
-    fun getTaskStream(taskId: String): Flow<Result<Task>>
+    fun getTaskStream(taskId: String): Flow<Task?>
 
-    suspend fun getTask(taskId: String): Result<Task>
+    suspend fun getTask(taskId: String): Task?
 
     suspend fun refreshTask(taskId: String)
 

app/src/main/java/com/example/android/architecture/blueprints/todoapp/data/source/TasksRepository.kt

@@ -16,7 +16,6 @@
 
 package com.example.android.architecture.blueprints.todoapp.data.source
 
-import com.example.android.architecture.blueprints.todoapp.data.Result
 import com.example.android.architecture.blueprints.todoapp.data.Task
 import kotlinx.coroutines.flow.Flow
 
@@ -25,15 +24,15 @@ import kotlinx.coroutines.flow.Flow
  */
 interface TasksRepository {
 
-    fun getTasksStream(): Flow<Result<List<Task>>>
+    fun getTasksStream(): Flow<List<Task>>
 
-    suspend fun getTasks(forceUpdate: Boolean = false): Result<List<Task>>
+    suspend fun getTasks(forceUpdate: Boolean = false): List<Task>
 
     suspend fun refreshTasks()
 
-    fun getTaskStream(taskId: String): Flow<Result<Task>>
+    fun getTaskStream(taskId: String): Flow<Task?>
 
-    suspend fun getTask(taskId: String, forceUpdate: Boolean = false): Result<Task>
+    suspend fun getTask(taskId: String, forceUpdate: Boolean = false): Task?
 
     suspend fun refreshTask(taskId: String)
 

app/src/main/java/com/example/android/architecture/blueprints/todoapp/data/source/local/TasksLocalDataSource.kt

@@ -16,15 +16,10 @@
 
 package com.example.android.architecture.blueprints.todoapp.data.source.local
 
-import com.example.android.architecture.blueprints.todoapp.data.Result
-import com.example.android.architecture.blueprints.todoapp.data.Result.Error
-import com.example.android.architecture.blueprints.todoapp.data.Result.Success
 import com.example.android.architecture.blueprints.todoapp.data.Task
 import com.example.android.architecture.blueprints.todoapp.data.source.TasksDataSource
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.Dispatchers
-import kotlinx.coroutines.flow.Flow
-import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.withContext
 
 /**
@@ -35,17 +30,9 @@ class TasksLocalDataSource internal constructor(
     private val ioDispatcher: CoroutineDispatcher = Dispatchers.IO
 ) : TasksDataSource {
 
-    override fun getTasksStream(): Flow<Result<List<Task>>> {
-        return tasksDao.observeTasks().map {
-            Success(it)
-        }
-    }
+    override fun getTasksStream() = tasksDao.observeTasks()
 
-    override fun getTaskStream(taskId: String): Flow<Result<Task>> {
-        return tasksDao.observeTaskById(taskId).map {
-            Success(it)
-        }
-    }
+    override fun getTaskStream(taskId: String) = tasksDao.observeTaskById(taskId)
 
     override suspend fun refreshTask(taskId: String) {
         // NO-OP
@@ -55,25 +42,12 @@ class TasksLocalDataSource internal constructor(
         // NO-OP
     }
 
-    override suspend fun getTasks(): Result<List<Task>> = withContext(ioDispatcher) {
-        return@withContext try {
-            Success(tasksDao.getTasks())
-        } catch (e: Exception) {
-            Error(e)
-        }
+    override suspend fun getTasks(): List<Task> = withContext(ioDispatcher) {
+        return@withContext tasksDao.getTasks()
     }
 
-    override suspend fun getTask(taskId: String): Result<Task> = withContext(ioDispatcher) {
-        try {
-            val task = tasksDao.getTaskById(taskId)
-            if (task != null) {
-                return@withContext Success(task)
-            } else {
-                return@withContext Error(Exception("Task not found!"))
-            }
-        } catch (e: Exception) {
-            return@withContext Error(e)
-        }
+    override suspend fun getTask(taskId: String): Task? = withContext(ioDispatcher) {
+        return@withContext tasksDao.getTaskById(taskId)
     }
 
     override suspend fun saveTask(task: Task) = withContext(ioDispatcher) {

app/src/main/java/com/example/android/architecture/blueprints/todoapp/data/source/remote/TasksRemoteDataSource.kt

@@ -16,9 +16,6 @@
 
 package com.example.android.architecture.blueprints.todoapp.data.source.remote
 
-import com.example.android.architecture.blueprints.todoapp.data.Result
-import com.example.android.architecture.blueprints.todoapp.data.Result.Error
-import com.example.android.architecture.blueprints.todoapp.data.Result.Success
 import com.example.android.architecture.blueprints.todoapp.data.Task
 import com.example.android.architecture.blueprints.todoapp.data.source.TasksDataSource
 import kotlinx.coroutines.delay
@@ -47,41 +44,31 @@ object TasksRemoteDataSource : TasksDataSource {
         observableTasks.value = getTasks()
     }
 
-    override fun getTaskStream(taskId: String): Flow<Result<Task>> {
+    override fun getTaskStream(taskId: String): Flow<Task?> {
         return observableTasks.map { tasks ->
-            when (tasks) {
-                is Error -> Error(tasks.exception)
-                is Success -> {
-                    val task = tasks.data.firstOrNull() { it.id == taskId }
-                        ?: return@map Error(Exception("Not found"))
-                    Success(task)
-                }
-            }
+            tasks.firstOrNull { it.id == taskId }
         }
     }
 
     override suspend fun refreshTask(taskId: String) {
         refreshTasks()
     }
 
-    override fun getTasksStream(): Flow<Result<List<Task>>> {
+    override fun getTasksStream(): Flow<List<Task>> {
         return observableTasks
     }
 
-    override suspend fun getTasks(): Result<List<Task>> {
+    override suspend fun getTasks(): List<Task> {
         // Simulate network by delaying the execution.
         val tasks = TASKS_SERVICE_DATA.values.toList()
         delay(SERVICE_LATENCY_IN_MILLIS)
-        return Success(tasks)
+        return tasks
     }
 
-    override suspend fun getTask(taskId: String): Result<Task> {
+    override suspend fun getTask(taskId: String): Task? {
         // Simulate network by delaying the execution.
         delay(SERVICE_LATENCY_IN_MILLIS)
-        TASKS_SERVICE_DATA[taskId]?.let {
-            return Success(it)
-        }
-        return Error(Exception("Task not found"))
+        return TASKS_SERVICE_DATA[taskId]
     }
 
     private fun addTask(title: String, description: String) {