如何使用Flutter监听Cloud Firestore中的文档更改？ [英] How to listen for document changes in Cloud Firestore using Flutter?

问题描述

我想有一个侦听器方法，如果发生更改，它会检查文档集合的更改。

I would like to have a listener method that checks for changes to a collection of documents if changes occur.

类似的东西：

import 'package:cloud_firestore/cloud_firestore.dart';


  Future<Null> checkFocChanges() async {
    Firestore.instance.runTransaction((Transaction tx) async {
      CollectionReference reference = Firestore.instance.collection('planets');
      reference.onSnapshot.listen((querySnapshot) {
        querySnapshot.docChanges.forEach((change) {
          // Do something with change
        });
      });
    });
  }

此处的错误是 onSnapshot 未在 CollectionReference 上定义。

The error here is that onSnapshot isn't defined on CollectionReference.

有任何想法吗？

推荐答案

通过 cloud_firestore 的文档，您可以看到来自 Query 的流可以通过 snapshots（）获得。

Reading through cloud_firestore's documentation you can see that a Stream from a Query can be obtained via snapshots().

为了让您理解，我将稍微转换一下代码：

For you to understand, I will transform your code just a tiny bit:

CollectionReference reference = Firestore.instance.collection('planets');
reference.snapshots().listen((querySnapshot) {
  querySnapshot.documentChanges.forEach((change) {
    // Do something with change
  });
});

您也不应该在事务中运行它。 Flutter方式是使用 StreamBuilder 直接从 cloud_firestore Dart 发布页：

You should also not run this in a transaction. The Flutter way of doing this is using a StreamBuilder, straight from the cloud_firestore Dart pub page:

StreamBuilder<QuerySnapshot>(
  stream: Firestore.instance.collection('books').snapshots(),
  builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
    if (!snapshot.hasData) return new Text('Loading...');
    return new ListView(
      children: snapshot.data.documents.map((DocumentSnapshot document) {
        return new ListTile(
          title: new Text(document['title']),
          subtitle: new Text(document['author']),
        );
      }).toList(),
    );
  },
);

如果您想了解更多信息，可以查看源代码，该文件已被很好地证明，在这里不言自明。

If you want to know any more, you can take a look at the source, it is well documented, where it is not self-explanatory.

还要注意，我将 docChanges 更改为 documentChanges 。您可以在 query_snapshot 文件。如果您使用的是IntelliJ或Android Studio之类的IDE，也可以非常轻松地单击其中的文件。

Also take note that I changed docChanges to documentChanges. You can see that in the query_snapshot file. If you are using an IDE like IntelliJ or Android Studio, it is also pretty easy to click through the files in it.

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