E/RecyclerView：没有附加适配器跳过布局

Question

我对@9​​87654322@ 中的RecyclerView 有疑问。在MainActivity 我有一个TabLayout 和一个ViewPager。我想在我的第一个标签中显示RecyclerView，但我不断收到以下错误：

E/RecyclerView：没有附加适配器；跳过布局

我尝试将回收器适配器初始化移动到OnViewCreated，但没有结果。

这是我的片段代码：

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

        listOfGreetings?.add(0, GreetingModel("Greeting 1", R.drawable.ic_launcher_background))
        listOfGreetings?.add(1, GreetingModel("Greeting 2", R.drawable.greeting_1))
        listOfGreetings?.add(2, GreetingModel("Greeting 3", R.drawable.greeting_1))
        listOfGreetings?.add(3, GreetingModel("Greeting 4", R.drawable.greeting_1))
        listOfGreetings?.add(4, GreetingModel("Greeting 5", R.drawable.greeting_1))
        listOfGreetings?.add(5, GreetingModel("Greeting 6", R.drawable.greeting_1))
        listOfGreetings?.add(6, GreetingModel("Greeting 7", R.drawable.greeting_1))
        listOfGreetings?.add(7, GreetingModel("Greeting 8", R.drawable.greeting_1))


        val recyclerView = container?.findViewById<RecyclerView>(R.id.recyclerView)
        val manager = LinearLayoutManager(activity)



        recyclerView?.setHasFixedSize(true)
        recyclerView?.layoutManager = manager



        recyclerView?.adapter = greetingAdapter

        return inflater.inflate(R.layout.fragment_category, container, false)

    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        greetingAdapter = GreetingAdapter(activity!!, listOfGreetings!!.toList())
    }

这是 XML：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
             xmlns:tools="http://schemas.android.com/tools"
             android:layout_width="match_parent"
             android:layout_height="match_parent" xmlns:app="http://schemas.android.com/apk/res-auto"
             tools:context=".CategoryFragment">

    <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/recyclerView"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_marginTop="3dp"
            />

</FrameLayout>

Answer 1

您看到此错误消息是因为recyclerView?.adapter = greetingAdapter 中的安全调用?. 将返回null，因此它不会被执行，因为您在视图膨胀之前调用它，即inflater.inflate(R.layout.fragment_category, container, false)，所以要解决那： 创建一个具有膨胀视图的值的变量，然后使用它从中获取视图并返回它就像这样：

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


listOfGreetings?.add(0, GreetingModel("Greeting 1", R.drawable.ic_launcher_background))
        listOfGreetings?.add(1, GreetingModel("Greeting 2", R.drawable.greeting_1))
        listOfGreetings?.add(2, GreetingModel("Greeting 3", R.drawable.greeting_1))
        listOfGreetings?.add(3, GreetingModel("Greeting 4", R.drawable.greeting_1))
        listOfGreetings?.add(4, GreetingModel("Greeting 5", R.drawable.greeting_1))
        listOfGreetings?.add(5, GreetingModel("Greeting 6", R.drawable.greeting_1))
        listOfGreetings?.add(6, GreetingModel("Greeting 7", R.drawable.greeting_1))
        listOfGreetings?.add(7, GreetingModel("Greeting 8", R.drawable.greeting_1))


 //This varaible will holds a reference to the inflated view.
 val view = inflater.inflate(R.layout.fragment_category, container, false)

 //Get the recyclerView from the inflated view.
 val recyclerView = view.findViewById<RecyclerView>(R.id.recyclerView)
 val manager = LinearLayoutManager(activity)

 //No need to the safe call ?. here because recyclerView won't be null. 
 recyclerView.setHasFixedSize(true)
 recyclerView.layoutManager = manager
 recyclerView.adapter = greetingAdapter

 return view 
}

此外，您在代码中过度使用了安全调用运算符 ?.。 listGreetings 可以变得更简单，您可以在 listGreeting 的对象上使用 apply()，在我们的例子中使用安全调用：

listOfGreetings?.apply {
            add(0, GreetingModel("Greeting 1", R.drawable.ic_launcher_background))
            add(1, GreetingModel("Greeting 2", R.drawable.greeting_1))
            add(2, GreetingModel("Greeting 3", R.drawable.greeting_1))
            add(3, GreetingModel("Greeting 4", R.drawable.greeting_1))
            add(4, GreetingModel("Greeting 5", R.drawable.greeting_1))
            add(5, GreetingModel("Greeting 6", R.drawable.greeting_1))
            add(6, GreetingModel("Greeting 7", R.drawable.greeting_1))
            add(7, GreetingModel("Greeting 8", R.drawable.greeting_1))
 }

这将检查如果listGreetings 不等于null，则将执行apply 块中的代码：

apply{
//block
}