flutter combine two stream where the second depends on the first? - flutter

Question

i have two collection,
users collection
like collection.
in my like i have the list of like with there id, i am now using stream to fetch the list like user but. so if the user change his profile image it cant be updated in the like collection, so what i did is after fetching the list, i pass the id to another stream to get upadate from Users collection. this alot of bioler plate code. i am looking for way to combine this stream together.
here is a sample code
StreamBuilder(
stream: firestore
.collection('Matches')
.doc(auth.currentUser.uid)
.collection('Match')
.orderBy('chatTimeStamp').snapshots(),
builder: (context, snapshot) {
if (!snapshot.hasData) {
return Container();
}
if (snapshot.connectionState ==
ConnectionState.waiting) {
return Center(child: CircularProgressIndicator());
}
if (snapshot.data.docs.isEmpty) {
return Align(
alignment: Alignment.center,
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
RippleAnimation(
repeat: true,
color: Colors.white,
minRadius: 100,
ripplesCount: 6,
child: Material(
elevation: 8.0,
shape: CircleBorder(),
child: CircleAvatar(
backgroundColor: themedata.darkTheme
? Colors.black
: Colors.white,
child: Image.asset(
'assets/1.png',
),
radius: 80.0,
),
),
),
Flexible(
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Text(
'No Message Yet!',
textAlign: TextAlign.center,
style: GoogleFonts.raleway(
textStyle: TextStyle(
color: Colors.white,
fontWeight: FontWeight.bold,
fontSize: 20,
),
),
),
),
),
],
),
);
}
return ListView.separated(
separatorBuilder: (_, index) => Padding(
padding:
EdgeInsets.only(left: 120.0, right: 40),
child: Divider(
color: Colors.white,
thickness: 1.0,
),
),
shrinkWrap: true,
itemCount: snapshot.data.docs.length,
itemBuilder: (context, index) {
final data =
snapshot.data.docs[index].data()['Match'];
//here is where it depend on the value
return StreamBuilder(
stream: firestore
.collection('users')
.doc(data['id'])
.snapshots(),
builder: (context, snapshotid) {
final active = snapshotid.data.data();
if (snapshotid.hasError) {
return Container();
}
if (snapshotid.connectionState ==
ConnectionState.waiting) {
return Center(
child: CircularProgressIndicator());
}
if (snapshotid.connectionState ==
ConnectionState.none) {
return Container();
}
if (!snapshotid.hasData) {
return Container();
}

Answer 1

For combining two streams you can use combine2 method from rxdart library. this library has all of the stream class features + some extra functionality which is really useful. for more detail you can see the official documentation here.
note: for using this library methods and functionalities you should also define streams by this library classes.
for example:
Stream stream, may be PublishSubject stream.