bottomNavigation：ReselectedListener：試圖調用虛擬方法的空對象引用

Question

我使用底部的導航在我的佈局，但是當我嘗試在我的主要活動寫一個關於點擊它的onCreate它給了我一個例外：

試圖在空對象上調用虛擬方法參考 private BottomNavigationView bottomNavigationView;

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    bottomNavigationView = (BottomNavigationView) findViewById(R.id.bottom_nav); 

    super.onCreate(savedInstanceState); 
    bottomNavigationView.setOnNavigationItemReselectedListener(new BottomNavigationView.OnNavigationItemReselectedListener() { 
     @Override 
     public void onNavigationItemReselected(@NonNull MenuItem item) { 

     } 
    }); 

Answer 1

改變這種

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    bottomNavigationView = (BottomNavigationView) findViewById(R.id.bottom_nav); 
    bottomNavigationView.setOnNavigationItemReselectedListener(new BottomNavigationView.OnNavigationItemReselectedListener() { 
     @Override 
     public void onNavigationItemReselected(@NonNull MenuItem item) { 

     } 
    });