Android Firebase，DataSnapshot转换为模型类

在使用Firebase数据库时，向模型类强制转换

DataSnapshot

时出现问题

我以DataSnapshot的形式接收信息，当我将其设置为String（）并记录时，我在数据库中看到了正确的信息（值）。但是当我尝试将其强制转换到我的模型类时，我看到了我的默认值（零值）

参考

@Override
public void onDataChange(DataSnapshot dataSnapshot){
    ResourcesFromActivity receivedData = dataSnapshot.getValue(ResourcesFromActivity.class);
    Log.e("Query Ref",dataSnapshot.getRef().toString());
    Log.e("Query DataS","\n "+dataSnapshot.toString() );
    Log.e("Query getVal()","\n "+ receivedData.toString() );
    Log.e("Query","\n "+ Long.toString(receivedData.getTotalMeters()));
    allLocations = receivedData.getMyLocationsList();
  (...)

E/Query getRef（）：https://*********/users/pZl7xHxREefHZu3Zgd7ZZBSJTmA2/activities

DataSnapshot.toString（）

E/查询数据：DataSnapshot{key=activities，value={29May201720:11:16={，elapsedTime=0，currentTime=170529201116，（…）， MyLocationList={（…）}//信息
//当前时刻的最后数据

铸造后的模型数据

E/Query getVal（）：ResourcesFromActivity{averageSpeed=0.0，maxSpeed=0.0，averageStrokeRate=0.0，totalMeters=0}//归零默认值

在单个节点上，它正在工作

{
  "rules": {
    "users": {
      "$uid": {
        ".read": "true",
        ".write": "$uid === auth.uid",
        "$userId" :{
        "activities":{
         "$activitieId": {
           ".read": "true",
           ".indexOn": ["currentTime"]
         }
        }
      }
      },

}
}

usersactiviesref=database.getReference（“消息”）； usersActivitiesRef.addValueEventListener（此）

代码：At onCreate（）：

    (mAuth.getCurrentUser() == null) {
        mAuth.getCurrentUser().reload();
    }
    else{
        mUser = FirebaseAuth.getInstance().getCurrentUser();
        usersActivitiesRef = database.getReference("users").child(mUser.getUid()).child("activities");//.endAt(true).limitToLast(1);

       // usersActivitiesRef = database.getReference("message");
        Query query = usersActivitiesRef.orderByChild("currentTime").limitToLast(1);
        Log.e("Query getRef()",query.getRef().toString());
        //usersActivitiesRef.addValueEventListener(this);
        query.addValueEventListener(this);
    }

@IgnoreExtraProperties
public class ResourcesFromActivity {

public String currentTime;
public long elapsedTime;
public String elapsedTimeStr;
public float averageSpeed;
public float maxSpeed;
public float averageStrokeRate;
public long totalMeters;
public List<MyLocation> myLocationsList = new ArrayList<>();
public List<Location> allLocations = new ArrayList<>();
public List<Float> allStrokes = new ArrayList<>();

public ResourcesFromActivity(){
    // Default constructor required for calls to DataSnapshot.getValue(ResourcesFromActivity.class)
} 
public ResourcesFromActivity(String currentTime, long elapsedTime, String elapsedTimeStr, float averageSpeed, float maxSpeed, float averageStrokeRate, long totalMeters, List<MyLocation> myLocationsList, List<Location> allLocations, List<Float> allStrokes) {
    this.currentTime = currentTime;
    this.elapsedTime = elapsedTime;
    this.elapsedTimeStr = elapsedTimeStr;
    this.averageSpeed = averageSpeed;
    this.maxSpeed = maxSpeed;
    this.averageStrokeRate = averageStrokeRate;
    this.totalMeters = totalMeters;
    this.myLocationsList = myLocationsList;
    this.allLocations = allLocations;
    this.allStrokes = allStrokes;
}

关于数据更改

@Override
public void onDataChange(DataSnapshot dataSnapshot){
    ResourcesFromActivity receivedData = dataSnapshot.getValue(ResourcesFromActivity.class);
    Log.e("Query Ref",dataSnapshot.getRef().toString());
    Log.e("Query DataS","\n "+dataSnapshot.toString() );
    Log.e("Query getVal()","\n "+ receivedData.toString() );
    Log.e("Query","\n "+ Long.toString(receivedData.getTotalMeters()));
    allLocations = receivedData.getMyLocationsList();
  (...)

型号：

    (mAuth.getCurrentUser() == null) {
        mAuth.getCurrentUser().reload();
    }
    else{
        mUser = FirebaseAuth.getInstance().getCurrentUser();
        usersActivitiesRef = database.getReference("users").child(mUser.getUid()).child("activities");//.endAt(true).limitToLast(1);

       // usersActivitiesRef = database.getReference("message");
        Query query = usersActivitiesRef.orderByChild("currentTime").limitToLast(1);
        Log.e("Query getRef()",query.getRef().toString());
        //usersActivitiesRef.addValueEventListener(this);
        query.addValueEventListener(this);
    }

@IgnoreExtraProperties
public class ResourcesFromActivity {

public String currentTime;
public long elapsedTime;
public String elapsedTimeStr;
public float averageSpeed;
public float maxSpeed;
public float averageStrokeRate;
public long totalMeters;
public List<MyLocation> myLocationsList = new ArrayList<>();
public List<Location> allLocations = new ArrayList<>();
public List<Float> allStrokes = new ArrayList<>();

public ResourcesFromActivity(){
    // Default constructor required for calls to DataSnapshot.getValue(ResourcesFromActivity.class)
} 
public ResourcesFromActivity(String currentTime, long elapsedTime, String elapsedTimeStr, float averageSpeed, float maxSpeed, float averageStrokeRate, long totalMeters, List<MyLocation> myLocationsList, List<Location> allLocations, List<Float> allStrokes) {
    this.currentTime = currentTime;
    this.elapsedTime = elapsedTime;
    this.elapsedTimeStr = elapsedTimeStr;
    this.averageSpeed = averageSpeed;
    this.maxSpeed = maxSpeed;
    this.averageStrokeRate = averageStrokeRate;
    this.totalMeters = totalMeters;
    this.myLocationsList = myLocationsList;
    this.allLocations = allLocations;
    this.allStrokes = allStrokes;
}

}

---

谢谢

这里的问题似乎是，作为dataSnapshot返回的内容与您期望得到的内容略有不匹配

在本例中，您得到的不是单个活动记录，而是活动记录的映射，在本例中，它包含一个项（或一个子项），因为这是您在查询中指定的

因此，这一点很重要，因为您不能直接将此映射设置为

ResourcesFromActivity

类，即使映射只包含一个项目，预期的字段也不匹配

使用当前设置执行此操作的一种方法是修改

onDataChange

，如下所示：

@Override
public void onDataChange(DataSnapshot dataSnapshot){
    for(DataSnapshot activitySnapShot: dataSnapshot.getChildren()){
        ResourcesFromActivity receivedData = activitySnapShot.getValue(ResourcesFromActivity.class);
    }
}

---

现在，我们正在迭代dataSnapshot的子项，以从子项中获取活动数据。在这种情况下，它只有一个子项，但您可以修改以处理多个子项。

我可以看到您的变量是私有的。您是否为它们创建了getter和setter？是否有一个公共构造函数接受所有变量bles作为参数？我固定了私有变量，但没有任何更改，{我使用了alt+Insert，默认值为private，}创建一个将这些变量作为参数的构造函数。以及公共getter和setter。同样，不工作。是否可能有多个构造函数出现问题？