Android：在片段中使用回收站视图的问题

Question

我在片段RecyclerView中使用ImagesliderFragment，首先它期望“ recyclerview不能为空”，因此在stackover流中，我得到一个答案，您应该使用以下行来初始化您的recyclerview： / p>

  frag_rv = view.findViewById(R.id.frag_rv) as RecyclerView

但是问题是它给了我错误。 only safe or non null asserted calls are allowed也是我的RecyclerView无法解决的问题，谁能向我解释这是什么问题？

ImagesliderFragment

class ImagesliderFragment : Fragment() {

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    arguments?.let {
    }
}

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    inflater.inflate(R.layout.fragment_imageslider, container, false)
    frag_rv = view.findViewById(R.id.frag_rv) as RecyclerView
    frag_rv.layoutManager = LinearLayoutManager(context, LinearLayout.HORIZONTAL, false)
    return view
}

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

}

Answer 1

尝试一下

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
) = 
    inflater.inflate(R.layout.fragment_imageslider, container, false).apply {
    frag_rv = findViewById(R.id.frag_rv) as RecyclerView //val frag_rv if it's not declared elsewhere 
    frag_rv.layoutManager = LinearLayoutManager(context, LinearLayout.HORIZONTAL, false)
}

Also now no need to do findViewById()

示例代码

class ImagesliderFragment : Fragment() {

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    arguments?.let {
    }
}

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


    val myView = inflater.inflate(R.layout.fragment_imageslider, container, false)
    val frag_rv = myView.findViewById(R.id.frag_rv) as RecyclerView
    frag_rv.layoutManager = LinearLayoutManager(context, LinearLayout.HORIZONTAL, false)

    return myView
}

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

}

Answer 2

您可以将onCreateView方法更改为：

5903

通过这种方式，视图会膨胀（通过inflater.inflate），您正在使用它来查找RecyclerView。

Answer 3

在使用view.findViewById之前，必须对其进行初始化，如下所示，还请在val之前使用frag_rv。

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

  // here you have to initialize your view
  View view = inflater.inflate(R.layout.fragment_imageslider, container, false)
  val frag_rv = view.findViewById(R.id.frag_rv) as RecyclerView
  frag_rv.layoutManager = LinearLayoutManager(context, LinearLayout.HORIZONTAL, false)

  return view
}

Answer 4

您仅应使用onCreateView方法来扩大视图并在onViewCreated方法中绑定iew

class ImagesliderFragment : Fragment() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?) = inflater.inflate(R.layout.fragment_imageslider, container, false)!!

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

        val frag_rv = view.findViewById<RecyclerView>(R.id.frag_rv)            frag_rv.layoutManager = LinearLayoutManager(context, LinearLayout.HORIZONTAL, 
            false)
    }
}