Android TableLayout上出现空指针异常

在onCreate（）之前声明了此项：

在onCreate（）中：

---

我很难看到侦听器是如何为空的。我还有其他NullPointerException，它们甚至在原语上声明null对象，包括可绘制PNG定义的int？

您忘记将布局设置为setContentView（）

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.TabLayout.addOnTabSelectedListener(android.support.design.widget.TabLayout$OnTabSelectedListener)' on a null object reference

TabLayout.OnTabSelectedListener listener;

TabLayout tabLayout = (TabLayout) findViewById(R.id.tabLayout);
listener = new TabLayout.OnTabSelectedListener(){
        @Override
        public void onTabSelected(TabLayout.Tab tab) {
            viewPager.setCurrentItem(tab.getPosition());
        }

        @Override
        public void onTabUnselected(TabLayout.Tab tab) {

        }

        @Override
        public void onTabReselected(TabLayout.Tab tab) {

        }
    };
    tabLayout.addOnTabSelectedListener(listener);