片段中的Kotlin RecolyerView-导航体系结构组件-空错误

Question

html" target="_blank">调试错误

E/AndroidRuntime：致命异常：主进程：com.projects.arise.myTestApp，PID:28285 java.lang.RuntimeException：无法启动activity ComponentInfo{com.projects.arise.myTestApp/com.projects.arise.myTestApp.MainActivity}：java.lang.IllegalStateException：rview_keys在Android.app.ActivityThread.PerformLaunchActivity（ActivityThread.java:2817)在Android.app.ActivityThread.HandleLaunchActivity（m.projects.arise.mytestapp.mainactivity.onCreate（mainactivity.kt:55)，位于Android.app.activity.performCreate（activity.java:6975)，位于Android.app.instrumentation.callactivityonCreate（instrumentation.java:1213)，位于Android.app.activitythread.performLaunchActivity（activitythread.java:2770)，位于Android.app.activitythread.handleLaunchActivity（activitythread.java:2892） 在android.app.activitythread.-wrap11（未知源：0） 在Android.app.ActivityThread$H.HandleMessage（ActivityThread.java:1593) 在android.os.handler.dispatchMessage(Handler.java:105) 在android.os.looper.loop(looper.java:164) 在android.app.activityThread.main（activityThread.java:6541) 在java.lang.Reflect.Method.Invoke（原生方法） 在com.android.internal.os.zygote$methodandargscaller.run(zygote.java:240) 在com.android.internal.os.zygoteinit.main（zygoteinit.java:767)

mainactivity.kt

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val host: NavHostFragment = supportFragmentManager
                .findFragmentById(R.id.nav_host_fragment) as NavHostFragment? ?: return

        val navController = host.navController
        setupBottomNavMenu(navController)
    }

    override fun onSupportNavigateUp(): Boolean {
        return Navigation.findNavController(this, R.id.nav_host_fragment).navigateUp()
    }

    private fun setupBottomNavMenu(navController: NavController) {
        findViewById<BottomNavigationView>(R.id.navigation)?.let { bottomNavView ->
            NavigationUI.setupWithNavController(bottomNavView, navController)
        }
    }
}

FragmentKeys.kt

class FragmentKeys : Fragment() {

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        setHasOptionsMenu(true)
        return inflater.inflate(R.layout.fragment_keys_layout, container, false)
    }

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

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

        //val rview_keys: RecyclerView = findViewById(R.id.rview_keys)
        rview_keys.layoutManager = LinearLayoutManager(context)
        rview_keys.adapter = AdapterKeys(KeysListObjects.keys)
    }
}

我注释掉了上面的一行，因为我在“findViewByID”上得到了一个“unresolved reference”错误。这行似乎没有必要，因为它不在其他人的代码中。例如：Kotlin Android碎片回收视图和上下文问题

class AdapterKeys(val keys: List<KeysList>) : RecyclerView.Adapter<AdapterKeys.KeysViewHolder>() {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): KeysViewHolder {
        val view = LayoutInflater.from(parent?.context).inflate(R.layout.list_item_keys, parent, false)
        return KeysViewHolder(view)
    }

    override fun getItemCount() : Int {
        return keys.size
    } //override fun getItemCount() = keys.size

    override fun onBindViewHolder(holder: KeysViewHolder, position: Int) {
        val keysList = keys[position]
        holder.setData(keysList, position)
    }

    inner class KeysViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {

        fun setData(keysList: KeysList?, position: Int) {
            itemView.tview_Keys.text = keysList!!.keysText
        }
    }
}

object KeysListObjects {
    val keys = listOf<KeysList>(
            KeysList("Testing1"),
            KeysList("Testing2"),
            KeysList("Testing3")
    )
}

Answer 1

您将得到错误，因为您注释了以下内容

//val rview_keys:RecyclerView=findViewById(r.id.rview_keys)

没有将rview_keys声明为变量。因此它将rview_keys视为一个视图，因为在您的活动中有一个id为rview_keys的视图。