Kotlin 类型不匹配，需要:x 找到:x? [英] Kotlin Type mismatch, required: x found: x?

问题描述

我发现很多参数都有错误

I find a lot of arguments have the error

Type mismatch
required: FragmentActivity
found: FragmentActivity?

我不确定解决此问题的最佳方法是什么.目前，我将该行包装在一个变量中?.let{ statement }

I'm not sure of what's the best way to address this problem. Currently, I wrap the line in a variable?.let{ statement }

meViewModel = ViewModelProviders.of((iMainActivity as Fragment).activity, vmf).get(MeViewModel::class.java) }

进入

val fragmentActivity = (iMainActivity as Fragment).activity

fragmentActivity?.let 
{ 
   meViewModel = ViewModelProviders.of(fragmentActivity, vmf).get(MeViewModel::class.java) 
}

这是解决这个问题的正确方法

is it the right way to approach this

推荐答案

简短回答:是的.

这意味着编译器不确定 s.th.是 !=null.如果您确定它不为空，您还可以使用:

This means that the compiler is not sure if s.th. is !=null. If you are sure that it is not null you can also use:

val fragmentActivity = (iMainActivity as Fragment).activity!!

这给你 FragmentActivity 而不是 FragmentActivity? 并且你不需要 ?.let{}

That gives you FragmentActivity instead of FragmentActivity? and you dont need the ?.let{}

请记住，这可能会引发 NPE，而

Keep in mind that that might throw a NPE, while the

fragmentActivity?.let { fragment ->
   meViewModel = ViewModelProviders.of(fragment, vmf).get(MeViewModel::class.java) 
}

根本不会执行 .let{} 中的块，这通常比 NPE 危害小.请参阅 https://kotlinlang.org/docs/reference/null-safety.html 了解更多.

would simply not execute the block within .let{}, which is often less harmful then a NPE. See https://kotlinlang.org/docs/reference/null-safety.html for more.

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