flutter - StatefulBuilder 与 StatefulWidget

Question

StatefulBuilder有什么区别和 StatefulWidget ?什么时候应该使用一个而不是另一个？
乍一看，它们似乎很相似。StatefulBuilder被定义为:

A platonic widget that both has state and calls a closure to obtain its child widget

虽然 StatefulBuilder被定义为:

A widget that has mutable state

Answer 1

一般使用 Builder在 build 中创建小部件树时内联方法。当您需要访问 context 时，这通常很有帮助。在您的小部件子树中。例如:
另见此 SO question

 @override
 Widget build(BuildContext context) {
   return Scaffold(
       appBar: AppBar(
         title: Text("Home"),
       ),
       body: Builder(builder: (thisLowerContext) {
         return RaisedButton(
             onPressed: () => Scaffold.of(thisLowerContext)
                 .showSnackBar(SnackBar(content: Text("button was clicked"))));
       }));
 }

使用 StatefulBuilder当您需要访问 setState那个子树。这将仅重建 StatefulBuilder及其子树。

class _SomeWidgetState extends State<HomeScreen> {
  Data data;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("Home"),
        ),
        body: StatefulBuilder(builder: (thisLowerContext, innerSetState) {
          if (data == null) {
            return RaisedButton(
                child: Text("Load data"),
                onPressed: () async {
                  Scaffold.of(thisLowerContext)
                      .showSnackBar(SnackBar(content: Text("Loading data...")));
                  var loadedData = await _loadData();
                  innerSetState(() => data = loadedData);
                });
          } else {
            return RaisedButton(
                child: Text("Reload data"),
                onPressed: () async {
                  Scaffold.of(thisLowerContext).showSnackBar(
                      SnackBar(content: Text("Reloading data...")));
                  var loadedData = await _reloadData();
                  innerSetState(() => data = loadedData);
                });
          }
        }));
  }
}