android - 如何为 Firebase 数据库序列化我的用户类并修复此错误？

Question

我正在尝试从 Firebase 数据库的 dataSnapshot 中检索更新的用户:

mRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            User atualizedUser = dataSnapshot.getValue(User.class);
            fName.setText(atualizedUser.getFirstName());
            lName.setText(atualizedUser.getLastName());
            profilePhoto.setProfileId(atualizedUser.getProfileId());
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

但是我在下面得到这个错误:

com.google.firebase.database.DatabaseException: Class bqs.bomqueso.Model.User is missing a constructor with no arguments
                                                            at com.google.android.gms.internal.zzbtg$zza.zze(Unknown Source)
                                                            at com.google.android.gms.internal.zzbtg$zza.zzaH(Unknown Source)
                                                            at com.google.android.gms.internal.zzbtg.zze(Unknown Source)
                                                            at com.google.android.gms.internal.zzbtg.zzb(Unknown Source)
                                                            at com.google.android.gms.internal.zzbtg.zza(Unknown Source)
                                                            at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)
                                                            at bqs.bomqueso.Activities.MainActivity$3.onDataChange(MainActivity.java:92)
                                                            at com.google.android.gms.internal.zzbpx.zza(Unknown Source)
                                                            at com.google.android.gms.internal.zzbqx.zzZS(Unknown Source)
                                                            at com.google.android.gms.internal.zzbra$1.run(Unknown Source)
                                                            at android.os.Handler.handleCallback(Handler.java:746)
                                                            at android.os.Handler.dispatchMessage(Handler.java:95)
                                                            at android.os.Looper.loop(Looper.java:148)
                                                            at android.app.ActivityThread.main(ActivityThread.java:5443)
                                                            at java.lang.reflect.Method.invoke(Native Method)
                                                            at     com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
                                                            at     com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)

这是我的用户类(这不是子类，我在单独的文件中创建它):

public class User {

private String firstName;
private String lastName;
private String profileId;

public User() { }

    public User(String fName, String lName, String id) {
        this.firstName = fName;
        this.lastName = lName;
        this.profileId = id;
    }

    public String getProfileId() {
        return profileId;
    }

    public void setProfileId(String id) { 
        this.profileId = id; 
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lName) { 
        this.lastName = lName; 
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String fName) { 
        this.firstName = fName; 
    }
}

我在这里找到了类似的问题，但我没有找到解决问题的方法，希望大家能帮助我，先谢谢了!

Answer 1

对于 Kotlin，如果您正在为 firebase 使用如下数据类，

data class UserModel(
        var userName: String,
        var userType: Int
)

然后你会得到类似这样的错误

com.google.firebase.database.DatabaseException: UserModel does not define a no-argument constructor. If you are using ProGuard, make sure these constructors are not stripped.

为此，您只需要初始化它的值。

data class UserModel(
        var userName: String = "",
        var userType: Int = 0
)