java - 在 Android 无法正常工作的情况下从 Firebase 检索数据

Question

我试图通过这样做来获取当前用户的详细信息:

Constants.USER_REF.orderByChild("email").equalTo(email).addListenerForSingleValueEvent(new ValueEventListener() {
     @Override
     public void onDataChange(DataSnapshot dataSnapshot) {
         if (dataSnapshot.exists() && dataSnapshot != null) {
             // User exists at this point, store it as currentUser variable.
             User currentUser = dataSnapshot.getValue(User.class);

             Log.i("THE_SNAPSHOT_AS_STRING:::", dataSnapshot.toString());

             // GETTING THE ERROR ON THE LINE BELOW!
             Log.i("THE_USERS_EMAIL:::", currentUser.getEmail());

         } else {
             // User does not exist at this point.
             Toast.makeText(TourContactActivity.this, "No user exists.", Toast.LENGTH_SHORT).show();

         }
      }
      @Override
      public void onCancelled(FirebaseError firebaseError) {

      }
});

我还在控制台日志中打印了以下内容，所以我知道它正在吸引正确的用户。

07-13 15:16:18.391 32277-32277/thepassapp.thompson.com.tomstours I/THE_SNAPSHOT_AS_STRING:::: DataSnapshot { key = users, value = {00845752-985f-4779-8eff-0c1e6a016ad8={tour_director_key=70af128e-777b-4c12-86f6-2952dbdc9185, last_name=River, email=rivers@gmail.com, location_latitude=42.4305, tour_id=n1337e, photo=http://chopu.herokuapp.com/parse/files/2enxs2j21mz9/7304a8917568d366a8ec43f5ab88ac6b_user.jpg, tour_director_name=Chuck Thoms, middle_name=, location_longitude=-73.5103, passenger_id=mcu79, location_updated=1468360656387, tour_director=f9e3z, first_name=Gene, provider=password}} }

这是我的 User.class

@JsonIgnoreProperties(ignoreUnknown=true)

public class User {

    private String uid;
    private String email;
    private String first_name;
    private String last_name;

    public User() {

        // empty default constructor, necessary for Firebase to be able to deserialize users

    }
    public User(String uid, String first_name, String last_name, String email) {
        this.uid = uid;
        this.first_name = first_name;
        this.last_name = last_name;
        this.email = email;
    }
    public String getEmail() {
        return email;
    }
    public String getFirstName() {
        return first_name;
    }
    public String getLastName() {
        return last_name;
    }

    @Override
    public String toString() {
        return "User{uid='"+uid+"', email='"+email+"', first_name='"+first_name+"', last_name='"+last_name+"\'}";

    }

}

我的问题实际上是从 User 类中检索此数据。我按照文档进行操作，但不断收到错误消息:

FATAL EXCEPTION: main

Process: passengerapp.veriguide.com.veriguidetours, PID: 32277
java.lang.NullPointerException: println needs a message

对我做错了什么有什么想法吗？注意:我评论了我收到错误的行。

Answer 1

您不能直接调用getValue()，因为dataSnapshot 有 child ，所以您需要在获取值之前迭代 child 。

@Override
public void onDataChange(DataSnapshot dataSnapshot) {
    if (dataSnapshot.exists()) {
        for (DataSnapshot data : dataSnapshot.getChildren()) {
            User currentUser = data.getValue(User.class);
            Log.i("THE_SNAPSHOT_AS_STRIN", data.toString());
            Log.i("THE_USERS_EMAIL:::", currentUser.getEmail());
        }
    } else {
        // User does not exist at this point.
    }
}

此外，您还必须为您的 User 类创建 setter，以便可以将值设置到该类。

public void setEmail(String email) {
    this.email = email;
}
public void setFirst_name(String first_name) {
    this.first_name = first_name;
}
public void setLast_name(String last_name) {
    this.last_name = last_name;
}
...

希望这有帮助:)