Question

我正在使用bottomnavigation视图开发android news应用程序，但是当我运行该应用程序时，却遇到了异常

Process: yodgorbek.komilov.musobaqayangiliklari, PID: 19590
    java.lang.RuntimeException: Unable to start activity ComponentInfo{yodgorbek.komilov.musobaqayangiliklari/yodgorbek.komilov.musobaqayangiliklari.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.material.bottomnavigation.BottomNavigationView.setOnNavigationItemSelectedListener(com.google.android.material.bottomnavigation.BottomNavigationView$OnNavigationItemSelectedListener)' on a null object reference`

MainActivity.kt下面 MainActivity类：AppCompatActivity（）{

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

   val  bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottom)



    bottomNavigationView.setOnNavigationItemSelectedListener {

        var selectedFragment = Fragment()
        when (it.itemId) {
            R.id.top_headline -> selectedFragment = TopHeadlinesFragment()
            R.id.espn_news -> selectedFragment = ESPNFragment()
            R.id.bbc_sport -> selectedFragment = BBCSportFragment()
            R.id.football_italia -> selectedFragment = FootballItaliaFragment()
        }
        val transaction = supportFragmentManager.beginTransaction()
        transaction.replace(R.id.frame_layout, selectedFragment)
        transaction.commit()
        return@setOnNavigationItemSelectedListener true

    }
}

}

activity_main.xml下面

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:layout_gravity="bottom"
        app:menu="@menu/bottomnews_nav"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
</FrameLayout>

Answer 1

在您的布局中，bottomNavigationView和framelayout都没有ID。两者都添加了ID

com.google.android.material.bottomnavigation.BottomNavigationView $ OnNavigationItemSelectedListener）”上的空对象引用

1 个答案: