How to store data of collection from firestore into a list?

问题

I am looking to store fetch data from firestore into a List which would contain data from all of its documents.

I defined list as :

List retrievedData = List();

next, on press of button, I wanted to print data in all documents of a specific collection. So, I did this:

RaisedButton(
        onPressed: () async {

          var collectionReferece = await Firestore.instance.collection('insults');
          collectionReferece.getDocuments().then((collectionSnapshot){
            retrievedData = collectionSnapshot.documents.toList();
          });

          print(retrievedData);
        },

I am expecting this in console:

I/flutter (11351): [{index: 200, title: This is a test 1},{index: 100, title: This is a test 2}]

But I get this:

I/flutter (11351): [Instance of 'DocumentSnapshot', Instance of 'DocumentSnapshot']

Also, I just want to store this data in a list or any other variable. Help me out. Thank you.

Edit:

I tried to use forEach but it keeps on adding on every press of button.

回答1:

If you want to:

retrieve data from firestore
add to list
create listview.builder

Then you can do the following, first declare the following variables under your State class:

class _MyHomePageState extends State<MyHomePage> {
  bool isFirstTime = false;
  List<DocumentSnapshot> datas = List<DocumentSnapshot>();

Next, create a method called getData() which will be referenced in onPressed:

      floatingActionButton: FloatingActionButton(
        onPressed: getData,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), 

  getData() async {
    if (!isFirstTime) {
      QuerySnapshot snap =
          await Firestore.instance.collection("insults").getDocuments();
      isFirstTime = true;
      setState(() {
        datas.addAll(snap.documents);
      });
    }
  }

Here on press of the FAB, you will get the data inside the insults collection. We use the boolean to only retrieve once per click. Inside the method dispose which you override:

  @override
  void dispose() {
    super.dispose();
    this.isFirstTime = false;
  }
}

You can assign isFirstTime to false again. Then to display the data, You can use the property body of AppBar, assign it to Center widget, and the Center widget will contain the listview:

      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: ListView.builder(
          itemCount: datas.length,
          itemBuilder: (context, index) {
            return ListTile(
              title: Text('${datas[index]["index"]}'),
              subtitle: Text('${datas[index]["title"]}'),
            );
          },
        ),

Using listview.builder, you will have a list in your screen and you dont have to use forEach to iterate a list. You just have to use the get operator [] to be able to get the data inside the list.

回答2:

Any code that needs access to the data from Firestore, need to be inside the then. So:

  var collectionReferece = await Firestore.instance.collection('insults');
  collectionReferece.getDocuments().then((collectionSnapshot){
    retrievedData = collectionSnapshot.documents.toList();
    print(retrievedData);
  });

But you'll typically want to separate the data loading out of the build() method, and use state or FutureBuilder to get the data from the database into the rendered output. Some examples of that:

Flutter/Firebase_Auth: a build function returned null for using state
How to use one field of firebase to login for another example of using state
how do i call async property in Widget build method for an example of using a FutureBuilder

回答3:

i think its because the .toList() method put those 2 documents just same datatype as "DocumentSnapshot" in the List. try printing this to be sure.

print(retrievedData[0]['title']);

来源：https://stackoverflow.com/questions/61547400/how-to-store-data-of-collection-from-firestore-into-a-list

标签

firebase

Flutter

dart

google-cloud-firestore