java - datasnapshot.getvalue() 不起作用并导致应用程序崩溃

Question

这个问题已经有答案了:

How can I serialize my User class for the Firebase Database and fix this error? (2 个回答)

已关闭 4 年前。

我正在尝试以 BusInformation.class 的形式从 firebase 实时数据库获取数据。但是我的应用程序在设置快照的类类型时崩溃了:ds.getValue(BusInformation.class);

我收到以下错误:

com.google.firebase.database.DatabaseException: Class com.example.muzammil.bustracking.app_classes.BusInformation does not define a no-argument constructor. If you are using ProGuard, make sure these constructors are not stripped.
        at com.google.android.gms.internal.firebase_database.zzku.zza(Unknown Source)
        at com.google.android.gms.internal.firebase_database.zzkt.zzb(Unknown Source)
        at com.google.android.gms.internal.firebase_database.zzkt.zza(Unknown Source)
        at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)

以下是 BuInformation.java 类的代码:

public class BusInformation {
    private String id, username,phone;
    private LatLng position;
    private String destination;

    public BusInformation(String id, String username, String phone,  String destination,LatLng position) {
        this.id = id;
        this.username = username;
        this.phone = phone;
        this.position = position;
        this.destination = destination;
    }
}

在 Firebase 数据库中，数据完全以这种形式存在。

从firebase获取数据的代码:

 public void getUpdatesFromFirebase(DataSnapshot dataSnapshot){
        for(DataSnapshot ds : dataSnapshot.getChildren()){
            if(ds.exists()) {
                busInfo = ds.getValue(BusInformation.class);  //App crashes at this point

            }

        }
    }

任何人请告诉我代码有什么问题......

Answer 1

BusInformation 未定义无参构造函数。

手动向其添加无参数构造函数:public BusInformation(){}

你的类应该是这样的:

public class BusInformation {
    private String id, username,phone;
    private LatLng position;
    private String destination;

    //no-argument constructor
    public BusInformation(){}

    public BusInformation(String id, String username, String phone,  String destination,LatLng position) {
        this.id = id;
        this.username = username;
        this.phone = phone;
        this.position = position;
        this.destination = destination;
    }
}