当我使用函数回调时我遇到问题

发布于 2025-01-12 22:49:00 字数 1432 浏览 4 评论 0原文

我有来自不同文件的自定义按钮小部件，然后我创建回调函数它可能会显示来自主函数的指针，当我运行时我遇到以下问题：问题

和这段代码，主布局：

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

void main() => runApp(MaterialApp(
      home: HomePage(),
    ));

class HomePage extends StatefulWidget {
  HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  int _counter = 0;
  void increment() {
    setState(() {
      _counter = _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          children: [
            Text('Result = ${_counter}'),
            SizedBox(
              height: 100,
            ),
            Inc(increment)
            // ElevatedButton(onPressed: increment, child: Text('-'))
          ],
        ),
      ),
    );
  }
}

和这个小部件自定义：

import 'package:flutter/material.dart';

class Inc extends StatelessWidget {
  final Function selectInc;
  Inc(this.selectInc);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      height: 100,
      child: ElevatedButton(onPressed: selectInc(), child: Text('+')),
    );
  }
}

我如何解决这个问题？

原文

i have custom button widget from different file, then i create callback function it might will showing pointer from main function, when i'm running i have issues this:
Issues

and this code, main layout:

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

void main() => runApp(MaterialApp(
      home: HomePage(),
    ));

class HomePage extends StatefulWidget {
  HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  int _counter = 0;
  void increment() {
    setState(() {
      _counter = _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          children: [
            Text('Result = ${_counter}'),
            SizedBox(
              height: 100,
            ),
            Inc(increment)
            // ElevatedButton(onPressed: increment, child: Text('-'))
          ],
        ),
      ),
    );
  }
}

and this widget custom:

import 'package:flutter/material.dart';

class Inc extends StatelessWidget {
  final Function selectInc;
  Inc(this.selectInc);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      height: 100,
      child: ElevatedButton(onPressed: selectInc(), child: Text('+')),
    );
  }
}

how i can solve this?

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淡紫姑娘！ 2025-01-19 22:49:00

onPressed: selectInc()

这是调用函数并使用结果。您只需将该函数用作参数：

onPressed: () => selectInc()

由于您的 selectInc 方法是一个 void 函数，即回调所需的确切类型，您也可以省略匿名函数包装器并直接传递您的回调：

onPressed: selectInc

但是，看来你需要更多的类型安全才能让编译器不抱怨。使

final Function selectInc;

看起来像这样：

final VoidCallback selectInc;

onPressed: selectInc()

This is calling the function and using the result. You need to use the function only as a parameter:

onPressed: () => selectInc()

Since your selectInc method is a void function, the exact type the callback requires, you could also omit the anonymous function wrapper and pass your callback directly: