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java - 处理 toString NullPointException，即使在检查了 !null 之后

问题描述

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 也表明Method invocation .toString may produce 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 = "";
    }
  }

既然我已经在检查了savedInstanceState，我还能检查什么？

标签： javaandroidnullpointerexception

解决方案

也许您没有将成功 charSecuence 设置为 bundle。

应该是这样的：

    @Override
    protected void onSaveInstanceState(final Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putCharSequence(KEY_LOCATION_NAME, location);
    }

如果你实现protected void onSaveInstanceState(final Bundle outState, PersistableBundle outPersistentState)它的另一种方法，请小心！

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