在带有kotlin和suspend函数的coroutine中返回

Question

IN行return@withContextcachedCategories，因为它不能只是返回cachedCateCategories。什么是@withContext？

代码已满：

@辛格尔顿class FoodMenuRemoteSource@Inject构造函数(private val foodMenuApi:foodMenuApi(｛

private var cachedCategories: List<FoodItem>? = null
suspend fun getFoodCategories(): List<FoodItem> = withContext(Dispatchers.IO) {
var cachedCategories = cachedCategories
if (cachedCategories == null) {
cachedCategories = foodMenuApi.getFoodCategories().mapCategoriesToItems()
[e-mail] = cachedCategories
}
return@withContext cachedCategories
}

Answer 1

lambda中不允许有非本地返回。这就是为什么@withContext是必要的。你看，那里的代码块实际上不是getFoodCategories的主体，而是作为withContext的第二个参数的lambda函数。此外，lambda中的最后一个表达式自动也是它的返回值，所以实际上可以像这个一样完全忽略return@withContext

private var cachedCategories: List<FoodItem>? = null
suspend fun getFoodCategories(): List<FoodItem> = withContext(Dispatchers.IO) {
var cachedCategories = cachedCategories
if (cachedCategories == null) {
cachedCategories = foodMenuApi.getFoodCategories().mapCategoriesToItems()
[e-mail] = cachedCategories
}
cachedCategories
}