一、需求来源

发现问题：

最近发现老代码中验证码倒计时按钮在低配机器上会出现数字乱闪的情况，查询资料之后发现是 jank 导致的问题。

解决办法：

思路是验证码接口请求成功之后，立即计算当前时间未来60s的目标时间点。定时器每秒轮训一次，查询当前时间距离目标时间点的剩余秒，然后显示在界面上。 通过mixin 做了倒计时逻辑抽离，方便二次封装组件。现成组件是 TimerButton，效果如下：

二、使用示例

TimerButton(
  onRequest: () async {
    await Future.delayed(Duration(milliseconds: 1));//假装在请求
    return true;
  },
),

三、源码

1、倒计时混入mixin： CountDownTimer,倒计时逻辑抽离

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter_templet_project/extension/extension_local.dart';

/// 倒计时
mixin CountDownTimer<T extends StatefulWidget> on State<T>, WidgetsBindingObserver {
  DateTime? _endTime;
  Timer? _timer;

  int get limitSecond => 60;

  final isCountingDownVN = ValueNotifier(false);
  late final countdownVN = ValueNotifier(limitSecond);

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    _timer?.cancel();
    super.dispose();
  }

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
  }

  // 处理 app 暂停/恢复（确保从后台回来能立即刷新）
  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (state == AppLifecycleState.resumed) {
      // app 回到前台，立刻重算一次
      _updateRemaining();
    }
  }

  /// 开始倒计时
  void startCountdown() {
    isCountingDownVN.value = true;
    countdownVN.value = limitSecond;

    _endTime = DateTime.now().add(Duration(seconds: limitSecond));
    _updateRemaining(); // 立即计算一次（避免 UI 延迟）
    _timer?.cancel();
    // 周期短一点以保证恢复后能尽快反映（但 setState 只有在秒数变化才触发）
    _timer = Timer.periodic(const Duration(seconds: 1), (_) => _updateRemaining());
  }

  void _updateRemaining() {
    if (_endTime == null) {
      return;
    }
    final secondsLeft = _endTime!.difference(DateTime.now()).inSeconds.clamp(0, limitSecond);
    DLog.d(["secondsLeft: $secondsLeft"]);
    if (secondsLeft <= 0) {
      isCountingDownVN.value = false;
      _timer?.cancel();
      _endTime = null;
    } else {
      countdownVN.value = secondsLeft;
    }
  }
}

2、TimerButton源码

// 验证码
class TimerButton extends StatefulWidget {
  const TimerButton({
    super.key,
    required this.onRequest,
  });

  final Future<bool> Function() onRequest;

  @override
  State<TimerButton> createState() => TimerButtonState();
}

/// 倒计时
class TimerButtonState extends State<TimerButton> with WidgetsBindingObserver, CountDownTimer {
  @override
  Widget build(BuildContext context) {
    return ValueListenableBuilder(
      valueListenable: isCountingDownVN,
      builder: (context, isCountingDown, child) {
        // final disabledBackgroundColor = themeProvider.isDark ? const Color(0xFF3A3A48) : const Color(0xFFDEDEDE);
        // final disabledForegroundColor = themeProvider.isDark ? const Color(0xFF7C7C85) : const Color(0xFFA7A7AE);

        return ElevatedButton(
          style: ElevatedButton.styleFrom(
            minimumSize: Size(60, 30),
            maximumSize: Size(100, 30),
            padding: EdgeInsets.symmetric(horizontal: 10, vertical: 4),
            tapTargetSize: MaterialTapTargetSize.shrinkWrap,
            backgroundColor: Colors.red,
            // disabledBackgroundColor: disabledBackgroundColor,
            foregroundColor: Colors.white,
            disabledForegroundColor: Colors.white,
            shape: RoundedRectangleBorder(
              borderRadius: BorderRadius.circular(4), // 设置圆角半径
            ),
            elevation: 0,
          ),
          onPressed: isCountingDown
              ? null
              : () async {
                  var res = await widget.onRequest();
                  if (res) {
                    startCountdown();
                  }
                },
          child: ValueListenableBuilder(
            valueListenable: countdownVN,
            builder: (context, value, child) {
              return Container(
                alignment: Alignment.center,
                child: Text(
                  isCountingDown ? '$value秒后重试' : '发送验证码',
                ),
              );
            },
          ),
        );
      },
    );
  }
}

最后、总结

倒计时逻辑实现起来并不复杂，但也算开发中遇到的疑难杂（高配机器永远不出现，低配经常出现），顺手做个记录。

github