java - 处理字符串空指针异常，即使在检查 !null 后也是如此

Question

我经常崩溃

Fatal Exception: java.lang.RuntimeException
Unable to start activity ComponentInfo{com.example.phocast/com.example.phocast.MainActivity}: java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.String java.lang.CharSequence.toString()' on a null object reference

AndroidStudio 还显示方法调用 .toString 可能会产生 NullPointException

我的代码是:

public class SunFragment extends Fragment {

  ArrayList<Object> sunsList;
  Typeface sunfont;
  Double Dlat;
  Double Dlang;

  private AdView mAdView;

  //to be called by the MainActivity
  public SunFragment() {
    // Required empty public constructor
  }

  private static final String KEY_LOCATION_NAME = "location_name";
  public String TAG = "SunFragment";
  public String location;//="No location name found";

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (savedInstanceState != null) {
      location = savedInstanceState.getCharSequence(KEY_LOCATION_NAME).toString();
      } else {
      location = "";
    }
  }

由于我已经在检查 savedInstanceState，我还可以检查什么？

Answer 1

您正在检查 savedInstance 是否为零，但对 getCharSequence(KEY_LOCATION_NAME) 的结果调用 toString 方法却没有已进行 null 检查。

你应该尝试这样的事情

if (savedInstance != null && savedInstance.getCharSequence(KEY_LOCATION_NAME) != null)
   location = savedInstance.getCharsequence(KEY_LOCATION_NAME).toString()