Question

我必须通过异步调用Room Database来更新UI，但是当我收到此错误时：android.view.ViewRootImpl $ CalledFromWrongThreadException：只有创建视图层次结构的原始线程才能触摸它的观点。

//收藏夹Presenter.kt

GlobalScope.launch {
    favoritesView.showFavorites(ProductProvider.getAllProducts() as ArrayList<Product>)
}

// ProductProvider.kt

fun getAllProducts() : MutableList<Product> {
    return dao.getAllProducts()
}

// ProductDao.kt

@Query("SELECT * FROM product")
fun getAllProducts(): MutableList<Product>

我需要通过ProductProvider更新UI，因为我将对所有实体使用可靠的解决方案。

Answer 1

您应该使用IO协程从Room中获取数据，并切换到主（UI）协程以更新视图。

尝试：

GlobalScope.launch(Dispatchers.IO) {
            val products = ProductProvider.getAllProducts() as ArrayList<Product>
            withContext(Dispatchers.Main) {
                favoritesView.showFavorites(products)
            }
        }

确保已安装Android Coroutine库，以便Main Dispatcher正确识别Android Main Thread。

api "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.1.1"

Answer 2

2.1室（当前为Alpha版）增加了对 Kotlin协程的支持。您可以执行以下操作：

将ProductDao和ProductProvider中的功能标记为暂停：

// ProductDao.kt
@Query("SELECT * FROM product")
suspend fun getAllProducts(): List<Product>

// ProductProvider.kt
suspend fun getAllProducts(): List<Product> = dao.getAllProducts()

在FavoritesPresenter中为协程创建本地作用域：

class FavoritesPresenter {
    private var favoritesView: FavoritesView? = null
    private val provider: ProductProvider = ...// initialize it somehow
    private var job: Job = Job()
    private val scope = CoroutineScope(job + Dispatchers.Main)

    fun getProducts() {
        scope.launch {
            favoritesView?.showFavorites(provider.getAllProducts())
        }
    }

    fun attachView(view: FavoritesView) {
        this.favoritesView = view
    }

    fun detachView() {
        job.cancel() // cancel the job when Activity or Fragment is destroyed
        favoritesView = null
    }

    interface FavoritesView {
        fun showFavorites(products: List<Product>)
    }
}

在FavoritesPresenter或Activity中使用Fragment：

class MainActivity : AppCompatActivity(), FavoritesPresenter.FavoritesView {
    lateinit var presenter: FavoritesPresenter
    override fun onCreate(savedInstanceState: Bundle?) {
       super.onCreate(savedInstanceState)
       // ...
       presenter = FavoritesPresenter()
       presenter.attachView(this)
       presenter.getProducts()

    }

    override fun onDestroy() {
        presenter.detachView()
        super.onDestroy()
    }

    override fun showFavorites(products: List<Product>) {
        // use products to update UI
    }
}

要使用 Dispatchers.Main 导入：

implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.1.1'

Answer 3

最好不要使用GlobalScope，而要使用自己的CoroutineContext，例如：

class YourActivity : CoroutineScope {
    private lateinit var job: Job

    // context for io thread
    override val coroutineContext: CoroutineContext
        get() = Dispatchers.IO + job

    override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    job = Job()
  }

    fun toDoSmth() {
        launch {
            // task, do smth in io thread
            withContext(Dispatchers.Main) {
              // do smth in main thread after task is finished
            }                  
        }
    }

   override fun onDestroy() {
      job.cancel()
      super.onDestroy()
   }
}

使用协程更新UI异步调用

3 个答案: