From 8e7487a9489a9e3d87bf614d327e4955f7a7b5f7 Mon Sep 17 00:00:00 2001
From: Jean-Philippe Levesque <jp.levesque@nventive.com>
Date: Tue, 18 Feb 2025 11:32:41 -0500
Subject: [PATCH] chore: Add getFromStream to have ViewModel properties that
 automatically update based on Stream sources.

---
 doc/Architecture.md                           |  6 ++++-
 .../lib/presentation/mvvm/mvvm_widget.dart    |  1 +
 src/app/lib/presentation/mvvm/view_model.dart | 27 +++++++++++++++++--
 src/cli/CHANGELOG.md                          |  3 +++
 4 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/doc/Architecture.md b/doc/Architecture.md
index 64ebed97..19490e44 100644
--- a/doc/Architecture.md
+++ b/doc/Architecture.md
@@ -121,13 +121,17 @@ These defined using accessors that call the `get` (or variants such as `getLazy`
 Here is an example of a ViewModel showcasing the usage of dynamic properties.
 ```dart
 class HomePageViewModel extends ViewModel {
-  // Regular property don't trigger rebuild if changed.
+  // Regular properties don't trigger rebuild if changed.
   final String title = 'Flutter Demo Home Page';
 
   // Dynamic properties triggers rebuild if changed.
   int get counter => get('counter', 0);
   set counter(int value) => set('counter', value);
 
+  // Dynamic properties can be made using complex sources, such as streams.
+  int get autoCounter => getFromStream('autoCounter',
+      () => Stream.periodic(const Duration(seconds: 1), (i) => i), 0);
+
   List<HomeItemViewModel> get items => getLazy(
       'items',
       () => [
diff --git a/src/app/lib/presentation/mvvm/mvvm_widget.dart b/src/app/lib/presentation/mvvm/mvvm_widget.dart
index 5c3c9388..4ff7bd91 100644
--- a/src/app/lib/presentation/mvvm/mvvm_widget.dart
+++ b/src/app/lib/presentation/mvvm/mvvm_widget.dart
@@ -55,6 +55,7 @@ class _MvvmWidgetState<TViewModel extends ViewModel>
   void dispose() {
     super.dispose();
     _viewModel.removeListener(onPropertyChanged);
+    _viewModel.dispose();
   }
 
   @override
diff --git a/src/app/lib/presentation/mvvm/view_model.dart b/src/app/lib/presentation/mvvm/view_model.dart
index 1e9ce569..e4613833 100644
--- a/src/app/lib/presentation/mvvm/view_model.dart
+++ b/src/app/lib/presentation/mvvm/view_model.dart
@@ -1,3 +1,4 @@
+import 'dart:async';
 import 'dart:collection';
 
 import 'package:flutter/foundation.dart';
@@ -5,17 +6,20 @@ import 'package:flutter/foundation.dart';
 abstract class ViewModel extends ChangeNotifier {
   final Map<String, dynamic> _properties = {};
   final HashSet<String> _propertiesToNotify = HashSet<String>();
+  final Map<String, StreamSubscription> _streamSubscriptions = {};
 
   bool _isRecordingPropertiesToNotify = false;
-  
+
   void startRecordingPropertiesToNotify() {
     _propertiesToNotify.clear();
     _isRecordingPropertiesToNotify = true;
   }
+
   void stopRecordingPropertiesToNotify() {
     _isRecordingPropertiesToNotify = false;
   }
-  void _recordPropertyName(String propertyName){
+
+  void _recordPropertyName(String propertyName) {
     if (_isRecordingPropertiesToNotify) {
       _propertiesToNotify.add(propertyName);
     }
@@ -41,4 +45,23 @@ abstract class ViewModel extends ChangeNotifier {
     _properties[propertyName] = value;
     notifyPropertyChanged(propertyName);
   }
+
+    T getFromStream<T>(String propertyName, Stream<T> Function() getStream, T initialValue) {
+    if (!_streamSubscriptions.containsKey(propertyName)) {
+      final subscription = getStream().listen((value) {
+        set(propertyName, value);
+      });
+      _streamSubscriptions[propertyName] = subscription;
+    }
+    return get(propertyName, initialValue);
+  }
+
+  @override
+  void dispose() {
+    super.dispose();
+    for (final subscription in _streamSubscriptions.values) {
+      subscription.cancel();
+    }
+    _streamSubscriptions.clear();
+  }
 }
diff --git a/src/cli/CHANGELOG.md b/src/cli/CHANGELOG.md
index 72b98e2f..022f5618 100644
--- a/src/cli/CHANGELOG.md
+++ b/src/cli/CHANGELOG.md
@@ -5,6 +5,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 
 Prefix your items with `(Template)` if the change is about the template and not the resulting application.
 
+## 0.24.1
+- Add `getFromStream` to have ViewModel properties that automatically update based on `Stream` sources.
+
 ## 0.24.0
 - Replace Riverpod in favor of a custom MVVM recipe with ViewModels to better align with the recommended [app architecture](https://docs.flutter.dev/app-architecture).