有沒有辦法在Flutter中呼叫另一個類的方法？

我傳遞的方法如下，但它非常復雜。我想直接呼叫方法而不傳遞方法。有沒有辦法做到這一點？

class Parent extends StatelessWidget {
  const Parent({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Child(onPressed: onPressed);
  }

  onPressed() {
    print("onPressed");
  }
}

class Child extends StatelessWidget {
  const Child({
    Key? key,
    required this.onPressed,
  }) : super(key: key);

  final Function() onPressed;

  @override
  Widget build(BuildContext context) {
    return Grandchild(onPressed: onPressed);
  }
}

class Grandchild extends StatelessWidget {
  const Grandchild({
    Key? key,
    required this.onPressed,
  }) : super(key: key);

  final Function() onPressed;

  @override
  Widget build(BuildContext context) {
    return FloatingActionButton(
      backgroundColor: Colors.black,
      mini: true,
      child: const Icon(
        Icons.cached,
        color: Colors.white,
      ),
      tooltip: 'Change Camera',
      onPressed: onPressed,
    );
  }
}

我正在設想像 Riverpod 的 StateNotifierProvider 之類的東西，你可以在其中傳遞方法，就像傳遞屬性一樣，但如果你能讓它變得更容易，那也很好。

uj5u.com熱心網友回復：

如果沒有狀態，則不必使用StateNotifierProvider。使用Provider：

final parentProvider = Provider<ParentNotifier>((ref) {
  return ParentNotifier();
});

class ParentNotifier {
  ParentNotifier();

  onPressed() {
    print("onPressed");
  }
}

在用戶界面中：

main() => runApp(const ProviderScope(child: MaterialApp(home: Parent())));

class Parent extends ConsumerWidget {
  const Parent({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    return const Child();
  }
}

class Child extends ConsumerWidget {
  const Child({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    return const Grandchild();
  }
}

class Grandchild extends ConsumerWidget {
  const Grandchild({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    return FloatingActionButton(
      backgroundColor: Colors.black,
      mini: true,
      tooltip: 'Change Camera',
      onPressed: () => ref.read(parentProvider).onPressed(),
      child: const Icon(Icons.cached, color: Colors.white),
    );
  }
}

通知類Child()，Grandchild()現在您可以使用const.

uj5u.com熱心網友回復：

你可以在 Dartpad 中試試這個。請注意，我將您的 Parent 轉換為一個簡單的類，該類僅具有您希望子小部件訪問的方法。

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

const Color darkBlue = Color.fromARGB(255, 18, 32, 47);

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(
        scaffoldBackgroundColor: darkBlue,
      ),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: Provider<ModelFromParent>(
                  create: (_) => ModelFromParent(),
                  child: const Parent()
          )
        ),
      ),
    );
  }
}



class ModelFromParent {
  onPressed() {
    print("onPressed");
  }
}

class Parent extends StatelessWidget {
  const Parent({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const Child();
  }
  
}

class Child extends StatelessWidget {
  const Child({
    Key? key
  }) : super(key: key);

  
  @override
  Widget build(BuildContext context) {
    return const Grandchild();
  }
}

class Grandchild extends StatelessWidget {
  const Grandchild({
    Key? key
  }) : super(key: key);

  

  @override
  Widget build(BuildContext context) {
    return FloatingActionButton(
      backgroundColor: Colors.black,
      mini: true,
      tooltip: 'Change Camera',
      onPressed: Provider.of<ModelFromParent>(context, listen:false).onPressed,
      child: const Icon(
        Icons.cached,
        color: Colors.white,
      )
    );
  }
}

uj5u.com熱心網友回復：

這是一個如何從孫子呼叫父方法的示例。希望這能回答你的問題。

class ParentScreen extends StatelessWidget {
  ParentScreen({super.key});



  void parentMethod() {
    print('calling parent method...');
  }

  @override
  Widget build(BuildContext context) {
    print('building parent ...');
    return Scaffold(
      appBar: AppBar(title: const Text('home page')),
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
          const  ChildWidget(
      
            )
          ],
        ),
      ),
    );
  }
}

class ChildWidget extends StatefulWidget {
  const ChildWidget({super.key, required this.grandChildKey});


  @override
  State<ChildWidget> createState() => ChildWidgetState();
}

class ChildWidgetState extends State<ChildWidget> {



  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.amber,
      child: Center(
        child: Column(
          children: [
            const Text(
              'child',
            ),
           const GrandChild(
      
            )
          ],
        ),
      ),
    );
  }
}

class GrandChild extends StatefulWidget {
  const GrandChild({
    super.key,
  });

  @override
  State<GrandChild> createState() => GrandChildState();
}

class GrandChildState extends State<GrandChild> {
  void callParent() {
  //for stateless parent:
    final parent = ParentScreen();
    parent.parentMethod();
    
    //if the parent is stateful:
//final parent = ParentScreenState();
//parent.parentMethod();
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisSize: MainAxisSize.min,
      children: [
        Container(
            color: Colors.amber,
            child: const Center(child: Text('grand child'))),
        ElevatedButton(onPressed: callParent, child: const Text('call parent'))
      ],
    );
  }
}

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