Kotlin 安全调用 (?.) 实现

Question

我可以用繁琐的方法解决它，所以如果您不post解决方法而是记录在案的解决方案，我将不胜感激。

我正在尝试将以下代码片段添加到片段的 onCreateView() 中，但是 "thanks" 安全调用（或我的代码设计）事情变得复杂了。 TabLayoutMediator(activity 部分 Kotlin 显示在 activity 之后添加安全调用 (?.) 的警告（相当于 Java 中的 getActivity）可能是 null .

Original code snippet before trying any solution

TabLayoutMediator(activity.findViewById(R.id.tabs), view.findViewById(R.id.view_pager),
                TabLayoutMediator.OnConfigureTabCallback { tab, position ->
                    // Styling each tab here
                    tab.text = mValueHeadlineCategoryList[position]
                }).attach()

1) Trying to solve by adding safe call (failed)

现在添加安全调用违反了 TabLayoutMediator 输入参数，我在 TabLayoutMediator 上收到 type mismatch Required:TabLayout Found:TabLayout? 警告。

TabLayoutMediator(activity?.findViewById(R.id.tabs), view.findViewById(R.id.view_pager),
            TabLayoutMediator.OnConfigureTabCallback { tab, position ->
                tab.text = mValueHeadlineCategoryList[position]
            }).attach()

2) Trying to solve by null check before safe call (failed)

添加空值检查，但现在 Kotlin 在 TabLayoutMediator(activity 部分发出警告 Smart cast to 'FragmentActivity' is impossible, because 'activity' is a property that has open or custom gette

if (activity != null) {
            TabLayoutMediator(activity.findViewById(R.id.tabs), view.findViewById(R.id.view_pager),
                TabLayoutMediator.OnConfigureTabCallback { tab, position ->
                    tab.text = mValueHeadlineCategoryList[position]
                }).attach()
        }

Answer 1

替换activitywith requireActivity().

Answer 2

简单修复：您可以这样做

   activity?.let { instance ->
            TabLayoutMediator(instance.findViewById(R.id.tabs), view.findViewById(R.id.view_pager),
                TabLayoutMediator.OnConfigureTabCallback { tab, position ->
                    tab.text = mValueHeadlineCategoryList[position]
                }).attach()
}

Kotlin 安全调用 (?.) 实现

Kotlin safe call (?.) implementation

android

kotlin

kotlin-null-safety