Flutter焦点检测插件 focus_detector 的使用

focus_detector 是一个用于检测Flutter应用中Widget是否获得或失去焦点的插件。它类似于Android中的onResume()/onPause()和iOS中的viewDidAppear()/viewDidDisappear()方法。

功能介绍

每当你的Widget在屏幕上出现或消失时，focus_detector都会触发回调函数。这些事件可能包括：

• 用户导航到另一个屏幕或从另一个屏幕返回。
• 当设备屏幕打开或关闭时。
• 用户切换到另一个应用程序或从后台切换回当前应用。
• 滚动导致Widget进入或离开屏幕视图。

使用方法

添加依赖

首先，在你的pubspec.yaml文件中添加focus_detector依赖：

dependencies:
  flutter:
    sdk: flutter
  focus_detector: ^1.0.4 # 请根据最新版本进行调整

然后运行flutter pub get来安装依赖。

示例代码

下面是一个完整的示例，展示了如何使用focus_detector插件来检测Widget的焦点变化情况。

import 'package:flutter/material.dart';
import 'package:focus_detector/focus_detector.dart';
import 'package:logger/logger.dart';

class FocusDetectorExample extends StatelessWidget {
  @override
  Widget build(BuildContext context) => FocusDetector(
        onFocusLost: () {
          logger.i(
            'Focus Lost.'
            '\nTriggered when either [onVisibilityLost] or [onForegroundLost] '
            'is called.'
            '\nEquivalent to onPause() on Android or viewDidDisappear() on iOS.',
          );
        },
        onFocusGained: () {
          logger.i(
            'Focus Gained.'
            '\nTriggered when either [onVisibilityGained] or [onForegroundGained] '
            'is called.'
            '\nEquivalent to onResume() on Android or viewDidAppear() on iOS.',
          );
        },
        onVisibilityLost: () {
          logger.i('Visibility Lost.\nIt means the widget is no longer visible within your app.');
        },
        onVisibilityGained: () {
          logger.i('Visibility Gained.\nIt means the widget is now visible within your app.');
        },
        onForegroundLost: () {
          logger.i(
            'Foreground Lost.'
            '\nIt means, for example, that the user sent your app to the background by opening another app or turned off the device\'s screen while your widget was visible.',
          );
        },
        onForegroundGained: () {
          logger.i(
            'Foreground Gained.'
            '\nIt means, for example, that the user switched back to your app or turned the device\'s screen back on while your widget was visible.',
          );
        },
        child: Material(
          child: Padding(
            padding: const EdgeInsets.all(16),
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                const Text(
                  'Send the app to the background or push another page and watch the console.',
                  textAlign: TextAlign.center,
                  style: TextStyle(fontSize: 20),
                ),
                const SizedBox(height: 20),
                ElevatedButton(
                  onPressed: () {
                    final route = MaterialPageRoute(builder: (_) => OtherPage());
                    Navigator.of(context).push(route);
                  },
                  child: const Text('PUSH ANOTHER PAGE'),
                )
              ],
            ),
          ),
        ),
      );
}

class OtherPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) => Scaffold(
        appBar: AppBar(),
        body: const Padding(
          padding: EdgeInsets.all(16),
          child: Center(
            child: Text(
              'Look at the console and return to the first screen.',
              textAlign: TextAlign.center,
              style: TextStyle(fontSize: 20),
            ),
          ),
        ),
      );
}

Logger logger = Logger(
  printer: PrettyPrinter(methodCount: 0, printTime: false),
);

void main() {
  runApp(MaterialApp(home: FocusDetectorExample(), theme: ThemeData()));
}

运行效果

当你运行这个示例程序，并尝试以下操作时，你会在控制台看到相应的日志输出：

• 点击按钮跳转到其他页面。
• 切换到其他应用再返回。
• 锁定屏幕再解锁。
• 滑动页面使Widget进入或离开视图范围。

通过这种方式，你可以更好地管理应用的状态，比如暂停和恢复视频播放、同步数据等。