Fixes subscription for Rx::bindStream

- add docs to bindStream for RxList,RxSet,RxMap,RxImpl.
- fixes the error of binding an ongoing Stream, without closing the Subscription when the observable gets closed.

@@ -179,13 +179,17 @@ class _RxImpl<T> implements RxInterface<T> {
   }
 
   Stream<T> get stream => subject.stream;
-
   StreamSubscription<T> listen(void Function(T) onData,
           {Function onError, void Function() onDone, bool cancelOnError}) =>
       stream.listen(onData, onError: onError, onDone: onDone);
 
-  /// Binds an existing stream to this Rx to keep the values in sync.
-  void bindStream(Stream<T> stream) => stream.listen((va) => value = va);
+  /// Binds an existing [Stream<T>] to this Rx<T> to keep the values in sync.
+  /// You can bind multiple sources to update the value.
+  /// Closing the subscription will happen automatically when the observer
+  /// Widget ([GetX] or [Obx]) gets unmounted from the Widget tree.
+  void bindStream(Stream<T> stream) {
+    _subscriptions[stream] = stream.listen((va) => value = va);
+  }
 
   Stream<R> map<R>(R mapper(T data)) => stream.map(mapper);
 }

 import 'dart:async';
+import 'dart:collection';
 import 'dart:math';
 
 import 'package:flutter/foundation.dart';
@@ -31,7 +32,7 @@ class RxList<E> implements List<E>, RxInterface<List<E>> {
   @override
   StreamController<List<E>> subject = StreamController.broadcast();
 
-  final Map<Stream<List<E>>, StreamSubscription> _subscriptions = {};
+  final _subscriptions = HashMap<Stream<List<E>>, StreamSubscription>();
 
   void operator []=(int index, E val) {
     _list[index] = val;
@@ -209,7 +210,13 @@ class RxList<E> implements List<E>, RxInterface<List<E>> {
   }) =>
       stream.listen(onData, onError: onError, onDone: onDone);
 
-  void bindStream(Stream<List<E>> stream) => stream.listen((va) => value = va);
+  /// Binds an existing [Stream<List>] to this [RxList].
+  /// You can bind multiple sources to update the value.
+  /// Closing the subscription will happen automatically when the observer
+  /// Widget ([GetX] or [Obx]) gets unmounted from the Widget tree.
+  void bindStream(Stream<List<E>> stream) {
+    _subscriptions[stream] = stream.listen((va) => value = va);
+  }
 
   @override
   E get first => value.first;

 import 'dart:async';
+import 'dart:collection';
 
 import 'package:flutter/foundation.dart';
 
@@ -13,7 +14,7 @@ class RxMap<K, V> implements RxInterface<Map<K, V>>, Map<K, V> {
 
   @override
   StreamController<Map<K, V>> subject = StreamController<Map<K, V>>.broadcast();
-  final Map<Stream<Map<K, V>>, StreamSubscription> _subscriptions = {};
+  final _subscriptions = HashMap<Stream<Map<K, V>>, StreamSubscription>();
 
   Map<K, V> _value;
 
@@ -62,8 +63,13 @@ class RxMap<K, V> implements RxInterface<Map<K, V>>, Map<K, V> {
           {Function onError, void Function() onDone, bool cancelOnError}) =>
       stream.listen(onData, onError: onError, onDone: onDone);
 
-  void bindStream(Stream<Map<K, V>> stream) =>
-      stream.listen((va) => value = va);
+  /// Binds an existing [Stream<Map>] to this [RxMap].
+  /// You can bind multiple sources to update the value.
+  /// Closing the subscription will happen automatically when the observer
+  /// Widget ([GetX] or [Obx]) gets unmounted from the Widget tree.
+  void bindStream(Stream<Map<K, V>> stream) {
+    _subscriptions[stream] = stream.listen((va) => value = va);
+  }
 
   void add(K key, V value) {
     _value[key] = value;

 import 'dart:async';
+import 'dart:collection';
 
 import 'package:flutter/foundation.dart';
 
@@ -27,7 +28,7 @@ class RxSet<E> implements Set<E>, RxInterface<Set<E>> {
   bool get isNotEmpty => value.isNotEmpty;
 
   StreamController<Set<E>> subject = StreamController<Set<E>>.broadcast();
-  final Map<Stream<Set<E>>, StreamSubscription> _subscriptions = {};
+  final _subscriptions = HashMap<Stream<Set<E>>, StreamSubscription>();
 
   /// Adds [item] only if [condition] resolves to true.
   void addIf(dynamic condition, E item) {
@@ -153,7 +154,13 @@ class RxSet<E> implements Set<E>, RxInterface<Set<E>> {
           {Function onError, void Function() onDone, bool cancelOnError}) =>
       stream.listen(onData, onError: onError, onDone: onDone);
 
-  void bindStream(Stream<Set<E>> stream) => stream.listen((va) => value = va);
+  /// Binds an existing [Stream<Set>] to this [RxSet].
+  /// You can bind multiple sources to update the value.
+  /// Closing the subscription will happen automatically when the observer
+  /// Widget ([GetX] or [Obx]) gets unmounted from the Widget tree.
+  void bindStream(Stream<Set<E>> stream) {
+    _subscriptions[stream] = stream.listen((va) => value = va);
+  }
 
   @override
   E get first => value.first;