My generic function for Retrofit interface creation get compiler error: inferred type is Class<T>? but Class<T!> was expected

Question

我在我的 Android (kotlin) 项目中使用 Retrofit。

我创建了我的界面：

interface StudentsInterface {
    @GET("foo/bar/{id}")
    suspend fun getStudent(@Path("id") myId: Int)
}

我创建了一个 MyClient class，我在其中定义了一个通用函数，用于从上面代码定义的任何接口创建端点服务：

class MyClient() {
    @Inject
    lateinit var  retrofit: Retrofit

    // this is my generic function
    fun <T> createService(interfaceClazz: Class<T>?): T {
        // Compiler error: Type mismatch: inferred type is Class<T>? but Class<T!> was expected
        return retrofit.create(interfaceClazz)
    }
}

所以在另一个class我可以:

val sService = myClient.createService(StudentsInterface::class.java)
...

但是当我构建项目时，我总是在代码行return retrofit.create(interfaceClazz)

中得到编译器错误：Type mismatch: inferred type is Class<T>? but Class<T!> was expected

为什么会出现此错误？如何摆脱它？

Answer 1

Retrofit 创建需要不可为 null 的参数。尝试使 interfaceClazz 不可为空

fun <T> createService(interfaceClazz: Class<T>): T {
    // No error now
    return retrofit.create(interfaceClazz)
}

My generic function for Retrofit interface creation get compiler error: inferred type is Class<T>? but Class<T!> was expected

My generic function for Retrofit interface creation get compiler error: inferred type is Class<T>? but Class<T!> was expected

generics

android

kotlin

retrofit

retrofit2