Support for Streams from query objects

README.md

@@ -158,6 +158,37 @@ scoreQuery.close();
 query.close();
 ```
 
+### Streams
+
+Streams can be created from queries.
+The streams can be extended with [rxdart](https://github.com/ReactiveX/rxdart);
+
+```dart
+    import "package:objectbox/src/observable.dart";
+
+    // final store = ...
+    final query = box.query(condition).build();
+    final queryStream = query.stream;
+    final sub1 = queryStream.listen((query) {
+      print(query.count());
+    });
+
+    // box.put ...
+
+    sub1.cancel();
+
+    final stream = query.findStream(limit:5);
+    final sub2 = stream.listen((list) {
+      // ...
+    });
+
+    // clean up
+    sub2.cancel();
+    store.unsubscribe();
+
+    store.close();
+```
+
 Help wanted
 -----------
 ObjectBox for Dart is still in an early stage with limited feature set (compared to other languages).

example/flutter/objectbox_demo/lib/main.dart

@@ -3,6 +3,9 @@ import 'package:objectbox/objectbox.dart';
 import 'package:intl/intl.dart';
 import 'package:path_provider/path_provider.dart';
 import 'objectbox.g.dart';
+import 'package:objectbox/src/observable.dart';
+import 'dart:async';
+import 'dart:io';
 
 @Entity()
 class Note {
@@ -11,14 +14,17 @@ class Note {
 
   String text;
   String comment;
-  int date; // TODO: use DateTime class
+  int date;
 
   Note();
 
   Note.construct(this.text) {
     date = DateTime.now().millisecondsSinceEpoch;
     print('constructed date: $date');
   }
+
+  get dateFormat => DateFormat('dd.MM.yyyy hh:mm:ss')
+      .format(DateTime.fromMillisecondsSinceEpoch(date));
 }
 
 void main() => runApp(MyApp());
@@ -43,143 +49,169 @@ class MyHomePage extends StatefulWidget {
   _MyHomePageState createState() => _MyHomePageState();
 }
 
-class _MyHomePageState extends State<MyHomePage> {
-  final _noteInputController = TextEditingController();
+class ViewModel {
   Store _store;
   Box<Note> _box;
-  List<Note> _notes = [];
+  Query<Note> _query;
+
+  ViewModel(Directory dir) {
+    _store = Store(getObjectBoxModel(), directory: dir.path + '/objectbox');
+    _box = Box<Note>(_store);
+
+    final dateProp = Note_.date;
+    final dummyCondition = dateProp.greaterThan(0);
+
+    _query = _box
+        .query(dummyCondition)
+        .order(dateProp, flags: Order.descending)
+        .build();
+  }
+
+  void addNote(Note note) => _box.put(note);
+
+  void removeNote(Note note) => _box.remove(note.id);
+
+  get queryStream => _query.findStream();
+
+  get allNotes => _query.find();
+
+  void dispose() {
+    _query.close();
+    _store.unsubscribe();
+    _store.close();
+  }
+}
+
+class _MyHomePageState extends State<MyHomePage> {
+  final _noteInputController = TextEditingController();
+  final _listController = StreamController<List<Note>>(sync:true);
+  Stream<List<Note>> _stream;
+  ViewModel _vm;
 
   void _addNote() {
     if (_noteInputController.text.isEmpty) return;
-    final newNote = Note.construct(_noteInputController.text);
-    newNote.id = _box.put(newNote);
-    setState(() => _notes.add(newNote));
+    _vm.addNote(Note.construct(_noteInputController.text));
     _noteInputController.text = '';
   }
 
-  void _removeNote(int index) {
-    _box.remove(_notes[index].id);
-    setState(() => _notes.removeAt(index));
-  }
-
   @override
   void initState() {
     super.initState();
 
     getApplicationDocumentsDirectory().then((dir) {
-      _store = Store(getObjectBoxModel(), directory: dir.path + '/objectbox');
-      _box = Box<Note>(_store);
-      final notesFromDb = _box.getAll();
-      setState(() => _notes = notesFromDb);
-      // TODO: don't show UI before this point
+      _vm = ViewModel(dir);
+      _stream = _listController.stream;
+
+      setState(() {});
+
+      _listController.add(_vm.allNotes);
+      _listController.addStream(_vm.queryStream);
     });
   }
 
   @override
   void dispose() {
     _noteInputController.dispose();
+    _listController.close();
+    _vm.dispose();
     super.dispose();
   }
 
-  @override
-  Widget build(BuildContext context) {
-    return Scaffold(
-      appBar: AppBar(
-        title: Text(widget.title),
-      ),
-      body: Column(
-        children: <Widget>[
-          Padding(
-            padding: EdgeInsets.all(20.0),
-            child: Row(
-              children: <Widget>[
-                Expanded(
+  GestureDetector Function(BuildContext, int) _itemBuilder(List<Note> notes) {
+    return (BuildContext context, int index) {
+      return GestureDetector(
+        onTap: () => _vm.removeNote(notes[index]),
+        child: Row(
+          children: <Widget>[
+            Expanded(
+              child: Container(
+                child: Padding(
+                  padding:
+                      EdgeInsets.symmetric(vertical: 18.0, horizontal: 10.0),
                   child: Column(
+                    crossAxisAlignment: CrossAxisAlignment.start,
                     children: <Widget>[
-                      Padding(
-                        padding: EdgeInsets.only(right: 10.0),
-                        child: TextField(
-                          decoration:
-                              InputDecoration(hintText: 'Enter new note'),
-                          controller: _noteInputController,
+                      Text(
+                        notes[index].text,
+                        style: TextStyle(
+                          fontSize: 15.0,
                         ),
                       ),
                       Padding(
-                        padding: EdgeInsets.only(top: 10.0, right: 10.0),
-                        child: Align(
-                          alignment: Alignment.centerRight,
-                          child: Text(
-                            'Click a note to remove it',
-                            style: TextStyle(
-                              fontSize: 11.0,
-                              color: Colors.grey,
-                            ),
+                        padding: EdgeInsets.only(top: 5.0),
+                        child: Text(
+                          'Added on ${notes[index].dateFormat}',
+                          style: TextStyle(
+                            fontSize: 12.0,
                           ),
                         ),
                       ),
                     ],
                   ),
                 ),
-                Column(
-                  children: <Widget>[
-                    RaisedButton(
-                      onPressed: _addNote,
-                      child: Text('Add'),
-                    )
-                  ],
-                )
-              ],
+                decoration: BoxDecoration(
+                    border: Border(bottom: BorderSide(color: Colors.black12))),
+              ),
             ),
-          ),
-          Expanded(
-            child: ListView.builder(
-              shrinkWrap: true,
-              padding: EdgeInsets.symmetric(horizontal: 20.0),
-              itemCount: _notes.length,
-              itemBuilder: (BuildContext context, int index) {
-                return GestureDetector(
-                  onTap: () => _removeNote(index),
-                  child: Row(
-                    children: <Widget>[
-                      Expanded(
-                        child: Container(
-                          child: Padding(
-                            padding: EdgeInsets.symmetric(
-                                vertical: 18.0, horizontal: 10.0),
-                            child: Column(
-                              crossAxisAlignment: CrossAxisAlignment.start,
-                              children: <Widget>[
-                                Text(
-                                  _notes[index].text,
-                                  style: TextStyle(
-                                    fontSize: 15.0,
-                                  ),
-                                ),
-                                Padding(
-                                  padding: EdgeInsets.only(top: 5.0),
-                                  child: Text(
-                                    "Added on ${DateFormat('dd.MM.yyyy hh:mm:ss').format(DateTime.fromMillisecondsSinceEpoch(_notes[index].date))}",
-                                    style: TextStyle(
-                                      fontSize: 12.0,
-                                    ),
-                                  ),
-                                ),
-                              ],
-                            ),
+          ],
+        ),
+      );
+    };
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(widget.title),
+      ),
+      body: Column(children: <Widget>[
+        Padding(
+          padding: EdgeInsets.all(20.0),
+          child: Row(
+            children: <Widget>[
+              Expanded(
+                child: Column(
+                  children: <Widget>[
+                    Padding(
+                      padding: EdgeInsets.symmetric(horizontal: 10.0),
+                      child: TextField(
+                        decoration:
+                            InputDecoration(hintText: 'Enter a new note'),
+                        controller: _noteInputController,
+                        onSubmitted: (String) => _addNote()
+                      ),
+                    ),
+                    Padding(
+                      padding: EdgeInsets.only(top: 10.0, right: 10.0),
+                      child: Align(
+                        alignment: Alignment.centerRight,
+                        child: Text(
+                          'Tap a note to remove it',
+                          style: TextStyle(
+                            fontSize: 11.0,
+                            color: Colors.grey,
                           ),
-                          decoration: BoxDecoration(
-                              border: Border(
-                                  bottom: BorderSide(color: Colors.black12))),
                         ),
                       ),
-                    ],
-                  ),
-                );
-              },
-            ),
+                    ),
+                  ],
+                ),
+              )
+            ],
           ),
-        ],
-      ),
+        ),
+        Expanded(
+            child: StreamBuilder<List<Note>>(
+                stream: _stream,
+                builder: (context, snapshot) {
+                  return ListView.builder(
+                      shrinkWrap: true,
+                      padding: EdgeInsets.symmetric(horizontal: 20.0),
+                      itemCount: snapshot.hasData ? snapshot.data.length : 0,
+                      itemBuilder: _itemBuilder(snapshot.data));
+                }))
+      ]),
     );
   }
 }

lib/src/bindings/bindings.dart

@@ -171,6 +171,11 @@ class _ObjectBoxBindings {
 
   obx_query_visit_dart_t obx_query_visit;
 
+  // Observers
+  obx_observe_t obx_observe;
+  obx_observe_single_type_t<int> obx_observe_single_type;
+  obx_observer_close_dart_t obx_observer_close;
+
   // query property
   obx_query_prop_t<int> obx_query_prop;
   obx_query_prop_close_t<int> obx_query_prop_close;
@@ -509,6 +514,11 @@ class _ObjectBoxBindings {
     obx_query_visit =
         _fn<obx_query_visit_native_t>('obx_query_visit').asFunction();
 
+    // observers
+    obx_observe = _fn<obx_observe_t>('obx_observe').asFunction();
+    obx_observe_single_type = _fn<obx_observe_single_type_t<Uint32>>('obx_observe_single_type').asFunction();
+    obx_observer_close = _fn<obx_observer_close_native_t>('obx_observer_close').asFunction();
+
     // query property
     obx_query_prop =
         _fn<obx_query_prop_t<Uint32>>('obx_query_prop').asFunction();

lib/src/bindings/signatures.dart

@@ -213,6 +213,17 @@ typedef obx_query_visit_dart_t = int Function(
     Pointer<NativeFunction<obx_data_visitor_native_t>> visitor,
     Pointer<Void> user_data);
 
+// observers
+
+typedef obx_observer_t = Void Function(Pointer<Void> user_data, Pointer<Uint32> entity_id, Uint32 type_ids_count);
+typedef obx_observer_single_type_native_t = Void Function(Pointer<Void> user_data);
+typedef obx_observer_single_type_dart_t = void Function(Pointer<Void> user_data);
+
+typedef obx_observe_t = Pointer<Void> Function(Pointer<Void> store, Pointer<NativeFunction<obx_observer_t>> callback, Pointer<Void> user_data);
+typedef obx_observe_single_type_t<T> = Pointer<Void> Function(Pointer<Void> store, T entity_id, Pointer<NativeFunction<obx_observer_single_type_native_t>> callback, Pointer<Void> user_data);
+typedef obx_observer_close_native_t = Void Function(Pointer<Void> observer);
+typedef obx_observer_close_dart_t = void Function(Pointer<Void> observer);
+
 // query property
 
 typedef obx_query_prop_t<T> = Pointer<Void> Function(