Firebase数据库:获取“无参数构造函数"尽管有错误 [英] Firebase Database: Getting "No-Argument Constructor" Error Despite Having It

问题描述

我试图在一个活动中写入数据，然后在另一个活动中读取数据.我的写作部分正在工作.对于我的阅读部分，我试图将getValue与我编写的类的参数一起使用.但我不断收到此错误:

I am trying to writing data in an activity and then reading it in another activity. My writing part is working. For my reading part, I am trying to use getValue with parameter of a class I wrote. But I keep getting this error:

com.google.firebase.database.DatabaseException:类ozhan.climb.MainActivity $ User没有定义无参数构造函数.如果您使用的是ProGuard，请确保没有剥离这些构造函数.

com.google.firebase.database.DatabaseException: Class ozhan.climb.MainActivity$User does not define a no-argument constructor. If you are using ProGuard, make sure these constructors are not stripped.

我在 getValue()中使用的班级:

class User {
    public String  Server,
            NeededRole,
            Role,
            SummonerName;

    User() {}

    public String get_Server() {
        return Server;
    }

    public String get_NeededRole() {
        return NeededRole;
    }

    public String get_Role() {
        return Role;
    }

    public String get_SummonerName() {
        return SummonerName;
    }
}

这是应该获取数据的代码:

and here is the code that should get data:

public void getUserData(){
    final TextView tv_sumName = findViewById(R.id.tv_sumName),
             tv_neededRole = findViewById(R.id.tv_neededrole),
             tv_userRole = findViewById(R.id.tv_userrole),
             tv_server = findViewById(R.id.tv_server);
    final String uid = Objects.requireNonNull(mAuth.getCurrentUser()).getUid();

    DatabaseReference usersDataRef = databaseRef.child("Users").child(uid);
    usersDataRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            User u = dataSnapshot.getValue(User.class);
            if (u != null) {
                tv_server.setText(u.Server);
                tv_neededRole.setText(u.NeededRole);
                tv_userRole.setText(u.Role);
                tv_sumName.setText(u.SummonerName);
            }
        }
        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {
        }
    });
}

推荐答案

该异常表明您的类是 ozhan.climb.MainActivity $ User -即，它是 MainActivity的内部类.

The exception says your class is ozhan.climb.MainActivity$User - i.e., it is an inner class of MainActivity.

内部类需要构造其外部类的实例.尽管错误消息肯定可以得到改善，但这不适用于Firebase数据库.

Inner classes require an instance of their outer class to construct. This won't work with Firebase Database, although the error message could definitely be improved.

您的User类应该是 static 类，该类没有相同的要求，即仅在包含类的实例中存在:

Your User class should be a static class, which does not have the same requirement to exist only within the instance of a containing class:

static class User {
  ...
}

这篇关于Firebase数据库:获取“无参数构造函数"尽管有错误的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！