cache time & garbage collection support added

onData & onError callbacks WIP

packages/fl_query/lib/query_builder.dart

@@ -8,10 +8,19 @@ class QueryBuilder<T extends Object, Outside> extends StatefulWidget {
   final QueryJob<T, Outside> job;
   final Outside externalData;
 
+  /// Called when the query returns new data, on query
+  /// refetch or query gets expired
+  final QueryListener<T>? onData;
+
+  /// Called when the query returns error
+  final QueryListener<dynamic>? onError;
+
   const QueryBuilder({
     required this.job,
     required this.externalData,
     required this.builder,
+    this.onData,
+    this.onError,
     Key? key,
   }) : super(key: key);
 
@@ -22,28 +31,51 @@ class QueryBuilder<T extends Object, Outside> extends StatefulWidget {
 
 class _QueryBuilderState<T extends Object, Outside>
     extends State<QueryBuilder<T, Outside>> {
+  late QueryBowl queryBowl;
+
   @override
   void initState() {
     super.initState();
     WidgetsBinding.instance.addPostFrameCallback((_) async {
-      await QueryBowl.of(context).fetchQuery<T, Outside>(widget.job,
-          externalData: widget.externalData);
+      queryBowl = QueryBowl.of(context);
+      await queryBowl.fetchQuery<T, Outside>(
+        widget.job,
+        externalData: widget.externalData,
+        onData: widget.onData,
+        onError: widget.onError,
+        mount: widget,
+      );
     });
   }
 
   @override
   void didUpdateWidget(covariant oldWidget) {
     if (oldWidget.externalData != widget.externalData) {
-      QueryBowl.of(context)
-          .fetchQuery(widget.job, externalData: widget.externalData);
+      queryBowl = QueryBowl.of(context);
+      // clearing up the old widget before adding the new updated one
+      // so unmounted zombie widgets don't get piled up
+      queryBowl.getQuery(widget.job.queryKey)?.unmount(oldWidget);
+      queryBowl.fetchQuery(
+        widget.job,
+        externalData: widget.externalData,
+        onData: widget.onData,
+        onError: widget.onError,
+        mount: widget,
+      );
     }
     super.didUpdateWidget(oldWidget);
   }
 
+  @override
+  void dispose() {
+    queryBowl.getQuery(widget.job.queryKey)?.unmount(widget);
+    super.dispose();
+  }
+
   @override
   Widget build(BuildContext context) {
-    final query =
-        QueryBowl.of(context).getQuery<T, Outside>(widget.job.queryKey);
+    queryBowl = QueryBowl.of(context);
+    final query = queryBowl.getQuery<T, Outside>(widget.job.queryKey);
     if (query == null) return Container();
     return widget.builder(context, query);
   }