Kotlin Android 片段回收服务和上下文问题
问题我想在片段中创建一个 recyclerView，但它显示错误“java.lang.IllegalStateException：recylerView_Main 不能为空
在 com.gph.bottomnavigation.FragmentMe.onCreateView (FragmentMe.kt:28) 上。 ”
但是相同的代码在片段中不起作用，它显示错误，所以我更改了“recylerView_Main.layoutManager=LinearLayoutManager(this)”到“recylerView_Main.layoutManager=LinearLayoutManager(context)”
它没有显示错误，我可以在模拟器中运行，但是当我单击片段的导航按钮时，应用程序停止并出现此错误。请帮忙。
这是 FragmentMe.kt 的代码：
class FragmentMe : Fragment() {
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
recylerView_Main.layoutManager = LinearLayoutManager(context)
recylerView_Main.adapter = Mainadapter()
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_me, container, false)
}
}
这是 MainActivity.kt 的代码：
class MainActivity : AppCompatActivity() {
val manager = supportFragmentManager
private val mOnNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
when (item.itemId) {
R.id.navigation_home -> {
//message.setText(R.string.title_home)
createFragmentQpon()
return@OnNavigationItemSelectedListener true
}
R.id.navigation_dashboard -> {
//message.setText(R.string.title_dashboard)
createFragmentMe()
return@OnNavigationItemSelectedListener true
}
R.id.navigation_notifications -> {
//message.setText(R.string.title_notifications)
createFragmentTools()
return@OnNavigationItemSelectedListener true
}
}
false
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
//Action Bar
val actionBar = supportActionBar
actionBar!!.setDisplayShowHomeEnabled(true)
actionBar.setBackgroundDrawable(ColorDrawable(Color.parseColor("#00FFFFFF")))
actionBar.setIcon(R.drawable.ic_home_black_24dp)
actionBar.setDisplayShowTitleEnabled(false)
createFragmentQpon()
navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener)
}
fun createFragmentQpon() {
val transaction = manager.beginTransaction()
val fragment = FragmentQpon()
transaction.replace(R.id.fragmentholder,fragment)
transaction.addToBackStack(null)
transaction.commit()
}
fun createFragmentMe() {
val transaction = manager.beginTransaction()
val fragment = FragmentMe()
transaction.replace(R.id.fragmentholder,fragment)
transaction.addToBackStack(null)
transaction.commit()
}
fun createFragmentTools() {
val transaction = manager.beginTransaction()
val fragment = FragmentTools()
transaction.replace(R.id.fragmentholder,fragment)
transaction.addToBackStack(null)
transaction.commit()
}
}
这是 Mainadapter.kt 的代码：
class Mainadapter: RecyclerView.Adapter<CustomViewHolder>() {
val videolist = listOf("aaa","bbbb","cccc")
override fun getItemCount(): Int {
return3
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CustomViewHolder {
val layoutInflater = LayoutInflater.from(parent?.context)
val cellForRow = layoutInflater.inflate(R.layout.tutorial_layout, parent, false)
return CustomViewHolder(cellForRow)
}
override fun onBindViewHolder(holder: CustomViewHolder, position: Int) {
var videoName = videolist.get(position)
holder.itemView.title.text = videoName
}
}
class CustomViewHolder(v: View): RecyclerView.ViewHolder(v) {
}
回答
移动此代码
recylerView_Main.layoutManager = LinearLayoutManager(context)
recylerView_Main.adapter = Mainadapter()
从 onCreateView 到 onActivityCreated
覆盖 onActivityCreated 并放置上面的代码。
代码中有两个错误：
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