我的应用程序有本地 SQLite（会议室）数据库我正在使用缓存数据的存储库设计模式（稍后我将它连接到远程存储库）。我有三个不同的数据库表 TableOne TableTwo 和 TableThree 。我对这些开发模式真的很陌生，无法找到准确的信息如何使用所有帮助都会有所帮助
我有以下问题：
以下是当前使用的缓存系统的代码：
/**
* Concrete implementation to load tasks from the data sources into a cache.
*
*
* For simplicity, this implements a dumb synchronisation between locally persisted data and data
* obtained from the server, by using the remote data source only if the local database doesn't
* exist or is empty.
*/
class TasksRepository(
val tasksRemoteDataSource: TasksDataSource,
val tasksLocalDataSource: TasksDataSource
) : TasksDataSource {
/**
* This variable has public visibility so it can be accessed from tests.
*/
var cachedTasks: LinkedHashMap<String, Task> = LinkedHashMap()
/**
* Marks the cache as invalid, to force an update the next time data is requested. This variable
* has package local visibility so it can be accessed from tests.
*/
var cacheIsDirty = false
/**
* Gets tasks from cache, local data source (SQLite) or remote data source, whichever is
* available first.
*
*
* Note: [LoadTasksCallback.onDataNotAvailable] is fired if all data sources fail to
* get the data.
*/
override fun getTasks(callback: TasksDataSource.LoadTasksCallback) {
// Respond immediately with cache if available and not dirty
if (cachedTasks.isNotEmpty() && !cacheIsDirty) {
callback.onTasksLoaded(ArrayList(cachedTasks.values))
return
}
if (cacheIsDirty) {
// If the cache is dirty we need to fetch new data from the network.
getTasksFromRemoteDataSource(callback)
} else {
// Query the local storage if available. If not, query the network.
tasksLocalDataSource.getTasks(object : TasksDataSource.LoadTasksCallback {
override fun onTasksLoaded(tasks: List<Task>) {
refreshCache(tasks)
callback.onTasksLoaded(ArrayList(cachedTasks.values))
}
override fun onDataNotAvailable() {
getTasksFromRemoteDataSource(callback)
}
})
}
}
override fun saveTask(task: Task) {
// Do in memory cache update to keep the app UI up to date
cacheAndPerform(task) {
tasksRemoteDataSource.saveTask(it)
tasksLocalDataSource.saveTask(it)
}
}
override fun completeTask(task: Task) {
// Do in memory cache update to keep the app UI up to date
cacheAndPerform(task) {
it.isCompleted = true
tasksRemoteDataSource.completeTask(it)
tasksLocalDataSource.completeTask(it)
}
}
override fun completeTask(taskId: String) {
getTaskWithId(taskId)?.let {
completeTask(it)
}
}
override fun activateTask(task: Task) {
// Do in memory cache update to keep the app UI up to date
cacheAndPerform(task) {
it.isCompleted = false
tasksRemoteDataSource.activateTask(it)
tasksLocalDataSource.activateTask(it)
}
}
override fun activateTask(taskId: String) {
getTaskWithId(taskId)?.let {
activateTask(it)
}
}
override fun clearCompletedTasks() {
tasksRemoteDataSource.clearCompletedTasks()
tasksLocalDataSource.clearCompletedTasks()
cachedTasks = cachedTasks.filterValues {
!it.isCompleted
} as LinkedHashMap<String, Task>
}
/**
* Gets tasks from local data source (sqlite) unless the table is new or empty. In that case it
* uses the network data source. This is done to simplify the sample.
*
*
* Note: [GetTaskCallback.onDataNotAvailable] is fired if both data sources fail to
* get the data.
*/
override fun getTask(taskId: String, callback: TasksDataSource.GetTaskCallback) {
val taskInCache = getTaskWithId(taskId)
// Respond immediately with cache if available
if (taskInCache != null) {
callback.onTaskLoaded(taskInCache)
return
}
// Load from server/persisted if needed.
// Is the task in the local data source? If not, query the network.
tasksLocalDataSource.getTask(taskId, object : TasksDataSource.GetTaskCallback {
override fun onTaskLoaded(task: Task) {
// Do in memory cache update to keep the app UI up to date
cacheAndPerform(task) {
callback.onTaskLoaded(it)
}
}
override fun onDataNotAvailable() {
tasksRemoteDataSource.getTask(taskId, object : TasksDataSource.GetTaskCallback {
override fun onTaskLoaded(task: Task) {
// Do in memory cache update to keep the app UI up to date
cacheAndPerform(task) {
callback.onTaskLoaded(it)
}
}
override fun onDataNotAvailable() {
callback.onDataNotAvailable()
}
})
}
})
}
override fun refreshTasks() {
cacheIsDirty = true
}
override fun deleteAllTasks() {
tasksRemoteDataSource.deleteAllTasks()
tasksLocalDataSource.deleteAllTasks()
cachedTasks.clear()
}
override fun deleteTask(taskId: String) {
tasksRemoteDataSource.deleteTask(taskId)
tasksLocalDataSource.deleteTask(taskId)
cachedTasks.remove(taskId)
}
private fun getTasksFromRemoteDataSource(callback: TasksDataSource.LoadTasksCallback) {
tasksRemoteDataSource.getTasks(object : TasksDataSource.LoadTasksCallback {
override fun onTasksLoaded(tasks: List<Task>) {
refreshCache(tasks)
refreshLocalDataSource(tasks)
callback.onTasksLoaded(ArrayList(cachedTasks.values))
}
override fun onDataNotAvailable() {
callback.onDataNotAvailable()
}
})
}
private fun refreshCache(tasks: List<Task>) {
cachedTasks.clear()
tasks.forEach {
cacheAndPerform(it) {}
}
cacheIsDirty = false
}
private fun refreshLocalDataSource(tasks: List<Task>) {
tasksLocalDataSource.deleteAllTasks()
for (task in tasks) {
tasksLocalDataSource.saveTask(task)
}
}
private fun getTaskWithId(id: String) = cachedTasks[id]
private inline fun cacheAndPerform(task: Task, perform: (Task) -> Unit) {
val cachedTask = Task(task.title, task.description, task.id).apply {
isCompleted = task.isCompleted
}
cachedTasks.put(cachedTask.id, cachedTask)
perform(cachedTask)
}
companion object {
private var INSTANCE: TasksRepository? = null
/**
* Returns the single instance of this class, creating it if necessary.
* @param tasksRemoteDataSource the backend data source
* *
* @param tasksLocalDataSource the device storage data source
* *
* @return the [TasksRepository] instance
*/
@JvmStatic fun getInstance(tasksRemoteDataSource: TasksDataSource,
tasksLocalDataSource: TasksDataSource) =
INSTANCE ?: synchronized(TasksRepository::class.java) {
INSTANCE ?: TasksRepository(tasksRemoteDataSource, tasksLocalDataSource)
.also { INSTANCE = it }
}
/**
* Used to force [getInstance] to create a new instance
* next time it's called.
*/
@JvmStatic fun destroyInstance() {
INSTANCE = null
}
}
}