问题描述
我正在按照文档在Firebase Firestore中创建分布式计数器,但是,我在其提供的代码上遇到了错误.
I'm following the documentation to create a distributed counter in Firebase Firestore, however, I'm getting an error on their provided code.
// counters/${ID}
public class Counter {
int numShards;
public Counter(int numShards) {
this.numShards = numShards;
}
}
// counters/${ID}/shards/${NUM}
public class Shard {
int count;
public Shard(int count) {
this.count = count;
}
}
运行createCounter方法时,它们已经定义
When running the createCounter method they've defined
public Task<Void> createCounter(final DocumentReference ref, final int numShards) {
// Initialize the counter document, then initialize each shard.
return ref.set(new Counter(numShards))
.continueWithTask(new Continuation<Void, Task<Void>>() {
@Override
public Task<Void> then(@NonNull Task<Void> task) throws Exception {
if (!task.isSuccessful()) {
throw task.getException();
}
List<Task<Void>> tasks = new ArrayList<>();
// Initialize each shard with count=0
for (int i = 0; i < numShards; i++) {
Task<Void> makeShard = ref.collection("shards")
.document(String.valueOf(i))
.set(new Shard(0));
tasks.add(makeShard);
}
return Tasks.whenAll(tasks);
}
});
}
我只是遇到了运行时异常
I simply get a Runtime Exception
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.enterprises.optaku.bvalyan.gametalk, PID: 8471
java.lang.RuntimeException: No properties to serialize found on class com.enterprises.optaku.bvalyan.gametalk.TopicVotingFragment$Counter
at com.google.firebase.firestore.g.zzg$zza.<init>(SourceFile:643)
at com.google.firebase.firestore.g.zzg.zza(SourceFile:331)
at com.google.firebase.firestore.g.zzg.zzb(SourceFile:152)
at com.google.firebase.firestore.g.zzg.zza(SourceFile:1085)
at com.google.firebase.firestore.UserDataConverter.convertPOJO(SourceFile:427)
at com.google.firebase.firestore.DocumentReference.set(SourceFile:165)
at com.enterprises.optaku.bvalyan.gametalk.TopicVotingFragment.createCounter(TopicVotingFragment.java:217)
at com.enterprises.optaku.bvalyan.gametalk.TopicVotingFragment.lambda$null$5$TopicVotingFragment(TopicVotingFragment.java:180)
即使我序列化了类,当我增加计数器时,它们的代码中仍然有一个异常
Even when I serialize the classes, I still get an exception in their code when I go to increment the counter
Shard shard = transaction.get(shardRef).toObject(Shard.class);
编译器抱怨在Shard类中没有无参数的构造函数.
The compiler complains there is no no-argument constructor in the Shard class.
我在这里不知所措,因为这是我能找到的唯一文档.有人成功实现了这一点,知道我在这里可能会缺少什么吗?
I'm at a loss here, as this is the only documentation I can find. Has anyone implemented this successfully and know what I could be missing here?
推荐答案
如错误消息所述,您的Shard类没有无参数构造函数.JavaBean类型类必须具有无参数构造函数,以便无法完全理解其他构造函数做什么的代码将其实例化.因此,您应该在代码中添加一个无参数的构造函数:
As the error message says, your Shard class has no no-argument constructor. JavaBean type classes must have a no-argument constructor in order for it to be instantiated by code that can't fully understand what the other constructors do. So, you should add a no-arg constructor to your code:
public class Shard {
int count;
public Shard() {} // this constructor has no arguments
public Shard(int count) {
this.count = count;
}
}
如果没有该构造函数,则Firestore SDK无法以可预测的方式创建 Shard
的实例.
Without that constructor, the Firestore SDK doesn't have a predictable way to create instances of Shard
.
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