我有一个用于监听 api 回调的抽象类,如下所示。 ApiRs 是每个 API 响应对象都继承自它的父对象
abstract class ApiCallback<in T : ApiRs> {
open fun onSucceed(apiRsModel: T) {}
open fun onFailed(code: Int,
message: String) {
}
}
我还写了一个函数来在请求api之前检查网络状态,如果网络没有连接,那么它会触发onFailed
fun isNetworkAvailable(apiCallback: ApiCallback<ApiRs>?,
context: Context): Boolean{
val connectivityManager = context
.getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager
val networkInfo = connectivityManager.activeNetworkInfo
// device network unreachable
if (networkInfo == null
|| !networkInfo.isConnected) {
// callback with network error
apiCallback?.onFailed(code, message)
return false
}
return true
}
参数类型ApiCallback<ApiRs>?
其实我想写成这样ApiCallback<? extends ApiRs>?
,但 Kotlin 没有通配符。如果我将通用替换为ApiCallback<out ApiRs>?
,它会显示错误
投影与 ApiCallback 相应类型参数的方差冲突
有什么办法可以解决吗?或者只是我对 Kotlin 泛型的概念有误?
2017/09/18 更新 - 正确的方法是:
方法 :
fun <T : ApiRs> isNetworkAvailable(apiCallback: ApiCallback<T>?,
context: Context): Boolean {
val connectivityManager = context
.getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager
val networkInfo = connectivityManager.activeNetworkInfo
// device network unreachable
if (networkInfo == null
|| !networkInfo.isConnected) {
// callback with network error
callbackWithFailed(
apiCallback,
ApiError.API_ERROR_CODE_0,
context.getString(R.string.api_error_code_0))
return false
}
return true
}