Merge pull request #12681 from nlebeck/taskviewmodel-refactor

Refactor `TaskViewModel` to track task-related state in a single `MutableLiveData` instance

Source/Android/app/src/main/java/org/dolphinemu/dolphinemu/activities/UserDataActivity.kt

@@ -102,10 +102,7 @@ class UserDataActivity : AppCompatActivity() {
             dialog.show(supportFragmentManager, UserDataImportWarningDialog.TAG)
         } else if (requestCode == REQUEST_CODE_EXPORT && resultCode == RESULT_OK) {
             taskViewModel.clear()
-            taskViewModel.task = {
-                val resultResource = exportUserData(data!!.data!!)
-                taskViewModel.setResult(resultResource)
-            }
+            taskViewModel.task = { exportUserData(data!!.data!!) }
 
             val arguments = Bundle()
             arguments.putInt(TaskDialog.KEY_TITLE, R.string.export_in_progress)

Source/Android/app/src/main/java/org/dolphinemu/dolphinemu/dialogs/TaskDialog.kt

@@ -34,14 +34,11 @@ class TaskDialog : DialogFragment() {
         val progressMessage = requireArguments().getInt(KEY_MESSAGE)
         if (progressMessage != 0) dialog.setMessage(resources.getString(progressMessage))
 
-        viewModel.isComplete.observe(this) { complete: Boolean ->
-            if (complete && viewModel.result.value != null) {
+        viewModel.result.observe(this) { result: Int? ->
+            if (result != null) {
                 dialog.dismiss()
                 val notificationArguments = Bundle()
-                notificationArguments.putInt(
-                    TaskCompleteDialog.KEY_MESSAGE,
-                    viewModel.result.value!!
-                )
+                notificationArguments.putInt(TaskCompleteDialog.KEY_MESSAGE, result)
 
                 val taskCompleteDialog = TaskCompleteDialog()
                 taskCompleteDialog.arguments = notificationArguments

Source/Android/app/src/main/java/org/dolphinemu/dolphinemu/dialogs/UserDataImportWarningDialog.kt

@@ -32,10 +32,8 @@ class UserDataImportWarningDialog : DialogFragment() {
                 taskArguments.putBoolean(TaskDialog.KEY_CANCELLABLE, false)
 
                 taskViewModel.task = {
-                    taskViewModel.setResult(
-                        (requireActivity() as UserDataActivity).importUserData(
-                            requireArguments().getString(KEY_URI_RESULT)!!.toUri()
-                        )
+                    (requireActivity() as UserDataActivity).importUserData(
+                        requireArguments().getString(KEY_URI_RESULT)!!.toUri()
                     )
                 }
 

Source/Android/app/src/main/java/org/dolphinemu/dolphinemu/model/TaskViewModel.kt

@@ -5,23 +5,49 @@ package org.dolphinemu.dolphinemu.model
 import androidx.lifecycle.LiveData
 import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.ViewModel
+import androidx.lifecycle.map
 import androidx.lifecycle.viewModelScope
 import kotlinx.coroutines.*
 
+/**
+ * A [ViewModel] associated with a task that runs on [Dispatchers.IO] and yields an integer result.
+ */
 class TaskViewModel : ViewModel() {
+    /** Represents the execution state of the task associated with this [TaskViewModel]. */
+    private interface State {
+        /** Returns true if the task has started running and false otherwise. */
+        fun hasStarted() : Boolean
+
+        /** Returns the task's result if it has completed or null otherwise. */
+        fun result() : Int?
+    }
+
+    private class NotStartedState : State {
+        override fun hasStarted() : Boolean { return false; }
+        override fun result() : Int? { return null; }
+    }
+
+    private class RunningState : State {
+        override fun hasStarted() : Boolean { return true; }
+        override fun result() : Int? { return null; }
+    }
+
+    private class CompletedState(private val result: Int) : State {
+        override fun hasStarted() : Boolean { return true; }
+        override fun result() : Int { return result; }
+    }
+
     var cancelled = false
     var mustRestartApp = false
 
-    private val _result = MutableLiveData<Int>()
-    val result: LiveData<Int> get() = _result
+    private val state = MutableLiveData<State>(NotStartedState())
 
-    private val _isComplete = MutableLiveData<Boolean>()
-    val isComplete: LiveData<Boolean> get() = _isComplete
+    /** Yields the result of [task] if it has completed or null otherwise. */
+    val result: LiveData<Int?> get() = state.map {
+        state -> state.result()
+    }
 
-    private val _isRunning = MutableLiveData<Boolean>()
-    val isRunning: LiveData<Boolean> get() = _isRunning
-
-    lateinit var task: () -> Unit
+    lateinit var task: () -> Int
     var onResultDismiss: (() -> Unit)? = null
 
     init {
@@ -29,28 +55,23 @@ class TaskViewModel : ViewModel() {
     }
 
     fun clear() {
-        _result.value = 0
-        _isComplete.value = false
+        state.value = NotStartedState()
         cancelled = false
         mustRestartApp = false
         onResultDismiss = null
-        _isRunning.value = false
     }
 
     fun runTask() {
-        if (isRunning.value == true) return
-        _isRunning.value = true
+        if (state.value!!.hasStarted()) {
+            return
+        }
+        state.value = RunningState()
 
         viewModelScope.launch {
             withContext(Dispatchers.IO) {
-                task.invoke()
-                _isRunning.postValue(false)
-                _isComplete.postValue(true)
+                val result = task.invoke()
+                state.postValue(CompletedState(result))
             }
         }
     }
-
-    fun setResult(result: Int) {
-        _result.postValue(result)
-    }
 }