java - 当我尝试比较数据库中的值和编辑文本输入时，出现 NullPointerException

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 6 年前。

因此，我尝试比较 2 个值，一个是 Firebase 中的“coinAmount”，它是一个 Long 值，另一个是 EditText 输入(这是一个字符串)。

基本上我想要实现的是，如果输入超过用户拥有的硬币数量，我想显示警告。

        String coinAmount = coinWrapper.getEditText().getText().toString();

        if (Long.parseLong(coinAmount) >= coinValue) {

          Toast.makeText(getApplicationContext(), "You don't have enough coins!",
              Toast.LENGTH_SHORT).show();
        } else {

          Intent intent = new Intent(getActivity(), FriendActivity.class);
          intent.putExtra("coin", coinAmount);
          intent.putExtra("choice", choice);
          startActivity(intent);
        }

我将用户输入作为字符串的原因是因为我稍后将将该值显示为文本，所以在比较时我将其解析为长整型。但是，当我运行该应用程序时，我收到此 NullPointerException:

E/AndroidRuntime: FATAL EXCEPTION: main
Process: ege.mevzubahis, PID: 13369
java.lang.NullPointerException
    at ege.mevzubahis.Fragments.BetsDialogFragment.onClick(BetsDialogFragment.java:135)
    at ege.mevzubahis.Fragments.BetsDialogFragment_ViewBinding$4.doClick(BetsDialogFragment_ViewBinding.java:70)
    at butterknife.internal.DebouncingOnClickListener.onClick(DebouncingOnClickListener.java:22)
    at android.view.View.performClick(View.java:4478)
    at android.view.View$PerformClick.run(View.java:18698)
    at android.os.Handler.handleCallback(Handler.java:733)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:149)
    at android.app.ActivityThread.main(ActivityThread.java:5257)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:515)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609)
    at dalvik.system.NativeStart.main(Native Method)

这是我尝试从 Firebase 获取 coinAmount 的部分:

sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
    userID=sharedPreferences.getString("userIDKey",null);


    mDatabase.child("Users").child(userID).addListenerForSingleValueEvent(new ValueEventListener() {
      @Override
      public void onDataChange(DataSnapshot dataSnapshot) {

        coinValue = (Long) dataSnapshot.child("coin").getValue();

      }

      @Override
      public void onCancelled(DatabaseError databaseError) {

        //Log.w(TAG, "loadPost:onCancelled", databaseError.toException());

      }
    });

这部分有错误:

if (Long.parseLong(coinAmount) >= coinValue) {

<小时/>

完整代码

public class BetsDialogFragment extends DialogFragment implements View.OnClickListener {

  @BindView(R.id.tv_match) TextView tv_match;
  @BindView(R.id.textView2) TextView textView2;
  @BindView(R.id.textInputLayout) TextInputLayout textInputLayout;
  @BindView(R.id.radioButton4) RadioButton radioButton4;
  @BindView(R.id.radioButton5) RadioButton radioButton5;
  @BindView(R.id.radioButton6) RadioButton radioButton6;
  @BindView(R.id.button2) Button sendButton;

  String matchName;
  private DatabaseReference mDatabase;
  private RadioGroup radioGroup;
  private String choice;
  private EditText editText;
  private TextInputLayout coinWrapper;
  public Long coinValue;

  SharedPreferences sharedPreferences;
  private String userID;

  @Nullable @Override
  public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
      Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.custom_dialog, null);
    matchName = getArguments().getString("betNameInPosition");
    mDatabase = FirebaseDatabase.getInstance().getReference();
    radioGroup = (RadioGroup) view.findViewById(R.id.radioGroup);
    editText = (EditText) view.findViewById(R.id.editText);
    coinWrapper = (TextInputLayout) view.findViewById(R.id.textInputLayout);
    sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
    userID=sharedPreferences.getString("userIDKey",null);


    mDatabase.child("Users").child(userID).addListenerForSingleValueEvent(new ValueEventListener() {
      @Override
      public void onDataChange(DataSnapshot dataSnapshot) {

        coinValue = (Long) dataSnapshot.child("coin").getValue();

        Log.v("coin value: ", coinValue.toString());

      }

      @Override
      public void onCancelled(DatabaseError databaseError) {

        //Log.w(TAG, "loadPost:onCancelled", databaseError.toException());

      }
    });

    mDatabase.child("Bets")
        .child("Sports")
        .child(matchName)
        .addListenerForSingleValueEvent(new ValueEventListener() {
          @Override public void onDataChange(DataSnapshot dataSnapshot) {
            try {
              Map<String, Object> map = (Map<String, Object>) dataSnapshot.getValue();
              String value = (String) map.get("matchname").toString();
              tv_match.setText(value);
              String durationValue = (String) map.get("duration").toString();
              textView2.setText("Due to: " + durationValue);

              coinValue = (Long) dataSnapshot.child("coin").getValue();
            } catch (Throwable t) {
              Log.e("trycatchFAIL", "b");
            }
          }

          @Override public void onCancelled(DatabaseError databaseError) {

          }
        });

    ButterKnife.bind(this, view);
    return view;
  }

  @OnClick({ R.id.radioButton4, R.id.radioButton5, R.id.radioButton6})
  public void onClick(View view) {

    switch (view.getId()) {
      case R.id.radioButton4:
        choice = "home";
        Toast.makeText(getApplicationContext(), "choice: Home", Toast.LENGTH_SHORT).show();
        break;
      case R.id.radioButton5:
        choice = "draw";
        Toast.makeText(getApplicationContext(), "choice: Draw", Toast.LENGTH_SHORT).show();
        break;
      case R.id.radioButton6:
        choice = "away";
        Toast.makeText(getApplicationContext(), "choice: Away", Toast.LENGTH_SHORT).show();
        break;

    }
  }

  @OnClick(R.id.button2)
  public void onClickSendButton(View view){
    String coinAmount = coinWrapper.getEditText().getText().toString();

    Log.v("coinAmount",coinAmount);

    if (Long.parseLong(coinAmount) >= coinValue) {

      Toast.makeText(getApplicationContext(), "You don't have enough coins!",
          Toast.LENGTH_SHORT).show();
    } else {

      Intent intent = new Intent(getActivity(), FriendActivity.class);
      intent.putExtra("coin", coinAmount);
      intent.putExtra("choice", choice);
      startActivity(intent);
    }


  }
}

Answer 1

if (Long.parseLong(coinAmount) >= coinValue).  

有问题:
如果 coinAmount 为 null，将抛出 java.lang.NumberFormatException:null所以看起来 coinValue 为空。
因为使用了“>=”，Java会尝试改变Long -> long。如果该项为 null，jvm 将抛出 java.lang.NullPointerException。