将支持库从 v-26.1.0 更新到 v-27.0.0 后，我的 fragment 中出现多个错误。

以下是其中一些错误的列表:

Error: Smart cast to 'Bundle' is impossible, because 'arguments' is a mutable property that could have been changed by this time.

Error: 'onCreateView' overrides nothing

Error: 'onViewCreated' overrides nothing

Error: Type mismatch: inferred type is View? but View was expected

Error: Type mismatch: inferred type is Context? but Context was expected

Error: Type mismatch: inferred type is FragmentActivity? but Context was expected

Error: Type mismatch: inferred type is FragmentActivity? but Context was expected

来自 android studio 的空 fragment 模板。

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    if (arguments != null) {
        mParam1 = arguments.getString(ARG_PARAM1)
        mParam2 = arguments.getString(ARG_PARAM2)
    }
}

override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    return inflater!!.inflate(R.layout.fragment_blank, container, false)
}

override fun onViewCreated(view: View?, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
}

最佳答案

所有这些错误的根本原因是在支持库 v-27.0.0 中添加了 @Nullable 和 @NonNull注解。
并且由于 kotlin 语言意识到可空性并且对于 Nullable 和 NonNull 具有不同的类型，这与 Java 不同。
如果没有这些注解，编译器就无法区分它们，Android Studio 正在尽最大努力推断出正确的类型。

TL;DR:更改类型以正确反射(reflect)可空性状态。

Error: Smart cast to 'Bundle' is impossible, because 'arguments' is a mutable property that could have been changed by this time.

更改 arguments.getString(ARG_NAME) ==> arguments?.getString(ARG_NAME) ?: ""

Error: 'onCreateView' overrides nothing

陈:

override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View?

==>

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View?

Error: 'onViewCreated' overrides nothing

改变:

override fun onViewCreated(view: View?, savedInstanceState: Bundle?)

==>

override fun onViewCreated(view: View, savedInstanceState: Bundle?)

Error: Type mismatch: inferred type is Context? but Context was expected

如果上下文作为参数传递给方法，只需使用快速修复将 getContext() 替换为 getContext()?.let{}
这同样适用于 kotlin 短版 context。

else if 用于调用某些方法将 getContext().someMethod() 替换为 getContext()?.someMethod()

同样适用于 kotlin 短版 context?.someMethod()。

Error: Type mismatch: inferred type is FragmentActivity? but Context was expected

使用先前错误的修复。

https://stackoverflow.com/questions/47016853/