bottomNavigation : ReselectedListener : 尝试在空对象引用上调用虚拟方法

Question

我在我的布局中使用底部导航，但是当我尝试在我的主要 activity oncreate 中编写一个点击它时，它给了我一个例外：

尝试在空对象引用上调用虚拟方法 私人 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

改变这个

    @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) {

        }
    });