Kotlin类型不匹配，必填: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，我将行包装在变量中..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) 
}

这是正确的方法

推荐答案

简短答案:是.

这意味着编译器不确定是否为s.th.是!=null.如果您确定它不为null，则也可以使用:

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!!

这将为您提供FragmentActivity而不是FragmentActivity?，并且您不需要?.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) 
}

根本不会在.let{}中执行该块，这通常不如NPE有害.参见 https://kotlinlang.org/docs/reference/null-safety.html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.

这篇关于Kotlin类型不匹配，必填:x找到:x?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！