onResume中的NullPointerException

Question

我有两个活动MainActivity和SecondActivity

活动主要活动.java

中的代码

public class MainActivity extends FragmentActivity implements OnMarkerClickListener {

@Override
 protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      getWindow().requestFeature(Window.FEATURE_NO_TITLE);
      setContentView(R.layout.activity_main_screen);
      databaseobj = new AppDatabase(MainActivity.this, null);
      listview = (ListView) findViewById(R.id.store_listview);
      noSavedMsg = (TextView) findViewById(R.id.no_msg);
      ..
      ..
      ..//Other code logic
      ..
 }

 @Override
 protected void onResume() {
      if (databaseobj.GetAll() != -1) { //NULL POINTER EXCEPTION
      listview.setVisibility(View.GONE);  //NULL POINTER EXCEPTION
      noSavedMsg.setVisibility(View.VISIBLE); //NULL POINTER EXCEPTION
      }
      super.onResume();
  }
}

从其他活动返回后，我收到空指针异常;

MainActivity - ＆gt;对SecondActivity的新意图

SecondActivity-＆gt; finish（）然后是MainActivity-＆gt; onResume（）NULL POINTER EXCEPTION

请帮忙！

Answer 1

您的TextView名称为noSavedMsg，但您正在尝试设置名为NoSavedMsg的视图的可见性......这两个名称不相同。

更改此行...

NoSavedMsg.setVisibility(View.VISIBLE);

为...

noSavedMsg.setVisibility(View.VISIBLE);

Answer 2

您确定需要那里的资金N吗？

NoSavedMsg.setVisibility(View.VISIBLE);

而不是：

noSavedMsg.setVisibility(View.VISIBLE);

Answer 3

databaseobj = new AppDatabase(MainActivity.this, null);
listview = (ListView) findViewById(R.id.store_listview);
noSavedMsg = (TextView) findViewById(R.id.no_msg);

将此代码添加到onResume方法中，看看它是否有效。