Flutter-使用FutureBuilder从Firestore获取数组(使用查询) [英] Flutter - Get array from Firestore with FutureBuilder (using query)

问题描述

我在这里非常困惑……如果我需要执行文档(在哪里)查询，使用FutureBuilder从Firestore中列出数组的正确语法是什么?

I'm confusing myself terribly here...what is the correct syntax for listing an array from Firestore with FutureBuilder if I need to perform a document (where) query?

Firestore数据库结构:

 - [companies]
   - [doc]

 - [gallery]
   - [doc]
    - [reference] <- (ie, companies/doc)
    - [gallery_images] // List these, but show only images that match where() query

这是我当前的代码:

Future<List<dynamic>> getGallery() async {
  var firestore = Firestore.instance;

  DocumentReference docRef = firestore.collection('companies').document(widget.docID);

  var ref = firestore.collection('galleries').where('companyRef', isEqualTo: docRef).getDocuments();

  return ref.get().then((datasnapshot) {
        if (datasnapshot.exists) {
        List<dynamic> imageArray = datasnapshot.data['gallery_images'].toList();
          return imageArray;
        } else {
          print("Please just work...");
        }
      },
    );
  }

FutureBuilder(
  future: getGallery(),
  builder: (context, AsyncSnapshot<List<dynamic>> snapshot) {
    if (snapshot.connectionState == ConnectionState.waiting) {
      return Center(
         child: Text("Loading..."),
        );
       } else {
    return GridView.builder(
    gridDelegate: new SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 2),
    itemCount: *length*,
    itemBuilder: (BuildContext context, int index) {
       return ViewGalleryItemThumbnail(
         viewGalleryItem: snapshot.data[index],
         ....

如果有人可以告诉我我要去哪里错了，我将不胜感激！

Would really appreciate if someone can show me where I'm going wrong!

推荐答案

目前尚不清楚Cloud Firestore模式的外观，但这看起来更有可能返回正确的动态列表. (请注意，通过将泛型添加到地图，您可以返回具体想要的列表-例如.map<SomeRealType>((snap) => snap.data['gallery_images']).)

It's not exactly clear what your Cloud Firestore schema looks like, but this looks more likely to return you the correct list of dynamics. (Note that by adding a generic to the map you could return a list of specifically what you want - e.g. .map<SomeRealType>((snap) => snap.data['gallery_images']).)

当您受困于FutureBuilder时，暂时恢复为有状态的小部件有时会很有用.覆盖initState，并调用经过稍微修改的getGallery，该末尾不会返回任何值，而是将其分配给setState内部的成员变量.这样，打印语句的机会就很多.另外，尝试将异步函数中的任何.then转换为线性的await系列.它使读取变得更容易(并且调试打印以合理的线性顺序出现).

When you're stuck with FutureBuilder it's sometimes useful to revert temporarily to a stateful widget. Override initState, and call a slightly modified getGallery which doesn't return a value at the end, but assigns it to a member variable inside setState. Plenty of opportunity for print statements that way. Additionally, try to convert any .thens in an async function into a linear series of awaits. It makes it easier to read (and your debug prints come out in a linear sensible order).

  Future<List<dynamic>> getGallery() async {
    var firestore = Firestore.instance;

    var docRef = firestore.collection('companies').document(widget.docID);

    var querySnap = await firestore
        .collection('galleries')
        .where('companyRef', isEqualTo: docRef)
        .getDocuments();

    return querySnap.documents
        .map((snap) => snap.data['gallery_images'])
        .toList();
  }

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