Question

我正在开发新闻应用程序，并且在MainViewModel.kt类中遇到以下错误类型不匹配：推断的类型为“除列表以外的其他”？是预期的

在我的MainViewModel.kt下面

class MainViewModel(
    private val sportNewsInterface: SportNewsInterface

) : ViewModel(), CoroutineScope {
    // Coroutine's background job
    private val job = Job()
    // Define default thread for Coroutine as Main and add job
    override val coroutineContext: CoroutineContext = Dispatchers.Main + job

    private val showLoading = MutableLiveData<Boolean>()
    private val sportList = MutableLiveData <List<SportNewsResponse>>()
    val showError = SingleLiveEvent<String>()

    fun loadNews() {
        // Show progressBar during the operation on the MAIN (default) thread
        showLoading.value = true
        // launch the Coroutine
        launch {
            // Switching from MAIN to IO thread for API operation
            // Update our data list with the new one from API
            val result = withContext(Dispatchers.IO) { sportNewsInterface.getNews()
            }
            // Hide progressBar once the operation is done on the MAIN (default) thread
            showLoading.value = false
            when (result) {


                is UseCaseResult.Success<*> -> {
                    sportList.value = result.data
                }
                is UseCaseResult.Error -> showError.value = result.exception.message
                 }
                }
            }



    override fun onCleared() {
        super.onCleared()
        // Clear our job when the linked activity is destroyed to avoid memory leaks
        job.cancel()
    }
}

UserCaseResult.kt以下

sealed class UseCaseResult<out T : Any> {
    class Success<out T : Any>(val data: T) : UseCaseResult<List<SportNewsResponse>>()

    class Error(val exception: Throwable) : UseCaseResult<Nothing>()
}

Answer 1

遇到了同样的问题，我清除了构建，然后再构建了一次，并且成功了。

Answer 2

看看您的Success类。您正在使用通用类型val data定义T，该类型由Any界定。在when块中，当您要检查它是否为UseCaseResult.Success的实例时，您正在使用星型投影，该星型投影会导致编译器以上限来推断结果：{{ 1}}。因此，UseCaseResult.Success<Any>的类型将被推断为result.data。

解决方案是：

如果Any仅具有列表类型的数据，则应忽略通用类型（当前UseCaseResult.Success类定义中的通用类型没有意义）：
```
Success
```
或：
```
class Success(val data: List<SportNewsResponse>) : UseCaseResult<List<SportNewsResponse>>()
```

或者您可以简单地将when子句更改为此：

class Success<out T: Any>(val data: List<T>) : UseCaseResult<List<T>>()

类型不匹配：推断的类型为List <SportNewsResponse>以外的任何类型？被期望

2 个答案: