问题描述
因此，我在多个Days集合中都有活动"文档，并且需要将所有活动"合并到一个列表中.我以为应该先循环集合，然后再循环活动，最后得到下面的代码，我不知道这是否是组合多个集合的最佳方法.更糟糕的是，我不知道何时可以将我的列表用于所有异步调用.有什么建议吗?谢谢！
So I have Activities documents in several Days collections and I need to combine all of the Activities in a list. I thought I should loop the collections and then loop the Activities and ended up with the code below which I don't know whether it's the best way to combine multiple collections. Even worse I don't know WHEN my list is ready to be used with all the asynchronous calls.Any advice? Thanks!
db.collection("calendar").get()
.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
@Override
public void onComplete(@NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
for (DocumentSnapshot ds : task.getResult().getDocuments()) {
ds.getReference().collection("thingstodo").get()
.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
@Override
public void onComplete(@NonNull Task<QuerySnapshot> task) {
for (DocumentSnapshot ds : task.getResult().getDocuments()) {
ScheduledItem item = ds.toObject(ScheduledItem.class);
itemsList.add(item);
}
}
});
}
}
});
推荐答案
CollectionReference (是Query的子类)返回任务，在文档准备就绪后即可解决.与其将侦听器添加到该单独的任务，不如将所有任务收集到一个列表中，然后将其传递给 Tasks.whenAllComplete() 在整个设置完成后做出响应.然后，您可以根据需要检查那里所有任务的结果.
The get() method you're using on CollectionReference (which is a subclass of Query) returns a Task that becomes resolved when the document is ready. Instead of adding a listener to that individual Task, collect all the tasks into a List, and pass that to Tasks.whenAllComplete() to respond when the entire set is complete. You can then examine the results of all the tasks there, as needed.
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