如何序列化Firebase数据库的User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) {

        }
    });
}

但我得到以下错误:

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User类(这不是一个子类,我在一个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; 
    }
}

我在这里发现了类似的问题,但我没有找到解决问题的方法,希望你们能帮助我,提前谢谢你们!

Answer 1

对于Kotlin,如果你使用下面的数据类作为firebase,

data class UserModel(
        var UserName: String,
        var UserType: Int
)

然后你会得到一个错误

com.google.firebase.database.DatabaseException:UserModel未定义无参数构造函数.如果您使用的是ProGuard,请确保不剥离这些构造函数.

因此,您需要初始化其值.

data class UserModel(
        var UserName: String = "",
        var UserType: Int = 0
)

Answer 2

创建一个不带参数的构造函数

public User() { } 正如板球提到的并序列化

public class User implements Serializable {

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;
}

}

如果这不符合要求，请记下