如何在flutter上实现事件侦听器或委托

Question

I have a main dart class in which the app bar is located and the app bar contains a refresh button. I'm using a navigation drawer to populate two other views f1 and f2.

From my main.dart how can I pass the refresh button clicks to the sub fragment kind of f1.dart so that I can refresh my contents on f1.dart

// State of Main
class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      drawer: Drawer(
        child: new Column(
          children: <Widget>[

////////////////////////////////////////////////////////////
                new FirstFragment(),
                new SecondFragment()
/////////////////////////////////////////////////////////////
          ],
        ),
      ),
      appBar: AppBar(
        title: Text(widget.title),
        actions: <Widget>[
          IconButton(
            icon: Icon(Icons.refresh),
            onPressed: () {
              print("refresh pressed");
/////////////////////////
         How to send this refresh pressed event to my FirstFragment class??
/////////////////////////
            },
            color: Colors.white,
          )
        ],
      ),
      body: _getDrawerItemWidget(_selectedDrawerIndex),
    );
  }

}

In Android, I've been using event listeners and for iOS, I can use delegates for the purpose. How can I achieve this on flutter/dart. ?

Answer 1

您可以传递回调，使用VoidCallback并在Main小部件上接收事件。

        class MainPage extends StatelessWidget {
          _onTapButton() {
            print("your event here");
          }

          @override
          Widget build(BuildContext context) {
            return Container(
              child: ChildPage(
                onTap: _onTapButton,
              ),
            );
          }
        }

        class ChildPage extends StatelessWidget {
          final VoidCallback onTap;

          const ChildPage({Key key, this.onTap}) : super(key: key);

          @override
          Widget build(BuildContext context) {
            return Container(
              child: RaisedButton(
                child: Text("Click Me"),
                onPressed: () {
                  //call to your callback  here
                  onTap();
                },
              ),
            );
          }
        } 

如果您想要相反的选择，则可以仅刷新父窗口小部件的状态并更改传递给片段的参数，也可以使用GlobalKey，如下例所示：

        class MainPage extends StatelessWidget {

          final GlobalKey<ChildPageState> _key = GlobalKey();

          _onTapButton() {
            _key.currentState.myMethod();
          }

          @override
          Widget build(BuildContext context) {
            return Container(
              child: Column(
                children: [
                  ChildPage(
                    key: _key,
                  ),
                  RaisedButton(
                    child: Text("Click me"),
                    onPressed: _onTapButton,
                  )
                ],
              )
            );
          }
        }

        class ChildPage extends StatefulWidget {
          const ChildPage({Key key}) : super(key: key);

          @override
          ChildPageState createState() {
            return new ChildPageState();
          }
        }

        class ChildPageState extends State<ChildPage> {

          myMethod(){
            print("called from parent");
          }

          @override
          Widget build(BuildContext context) {
            return Container(
              child: Text("Click Me"),
            );
          }
        }