Why I cannot use where & orderby from FirebaseFirestore in flutter

in my code

StreamBuilder(
        stream: FirebaseFirestore.instance
            .collection('Posts')
            .where('imageType', isEqualTo: 'image')
            .orderBy('time', descending: true) 
            .snapshots(),

I will got error.

itemCount: snapshot.data!.docs.length

Error code

Exception has occurred.
_CastError (Null check operator used on a null value)

Where has problem?

CodePudding user response：

Data can be null, so using your snapshot.data! bang operator will give you that error. By using ! you basically tell the compiler that you promise the value will not be null at that point. However, it is in your case :)

Consider implementing some sort of loading indicator that is returned instead of whatever you are building when you got actual data :)

The where and orderBy have nothing to do with your issue btw.

CodePudding user response：

You can use something like a loading indicator to wait until data comes so it will not be null

For example in your stream builder you can use something like

if (!snapshot.hasData)
   return Center(
       child: CircularProgressIndicator());
return TheWidgetYouWantToBuildWhenDataComes();