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小编典典

颤动倒数计时器

flutter

如何将传递的值放入构造中，使计时器
四舍五入到小数点后一位并显示在RaisedButton的子文本中？
我尝试过但没有运气。我设法使用
一个简单的Timer 来使回调函数起作用，但没有周期性，并且
文本中没有实时更新值…

import 'package:flutter/material.dart';
import 'dart:ui';
import 'dart:async';

class TimerButton extends StatefulWidget {
  final Duration timerTastoPremuto;


  TimerButton(this.timerTastoPremuto);

  @override
  _TimerButtonState createState() => _TimerButtonState();
}

class _TimerButtonState extends State<TimerButton> {
  @override
  Widget build(BuildContext context) {
    return Container(
      margin: EdgeInsets.all(5.0),
      height: 135.0,
      width: 135.0,
      child: new RaisedButton(
        elevation: 100.0,
        color: Colors.white.withOpacity(.8),
        highlightElevation: 0.0,
        onPressed: () {
          int _start = widget.timerTastoPremuto.inMilliseconds;

          const oneDecimal = const Duration(milliseconds: 100);
          Timer _timer = new Timer.periodic(
              oneDecimal,
                  (Timer timer) =>
                  setState(() {
                    if (_start < 100) {
                      _timer.cancel();
                    } else {
                      _start = _start - 100;
                    }
                  }));

        },
        splashColor: Colors.red,
        highlightColor: Colors.red,
        //shape: RoundedRectangleBorder e tutto il resto uguale
        shape: BeveledRectangleBorder(
            side: BorderSide(color: Colors.black, width: 2.5),
            borderRadius: new BorderRadius.circular(15.0)),
        child: new Text(
          "$_start",
          style: new TextStyle(fontFamily: "Minim", fontSize: 50.0),
        ),
      ),
    );
  }
}

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2020-08-13

共1个答案

小编典典

Here is an example using
Timer.periodic :

Countdown starts from 10 to 0 on button click :

import 'dart:async';

[...]

Timer _timer;
int _start = 10;

void startTimer() {
  const oneSec = const Duration(seconds: 1);
  _timer = new Timer.periodic(
    oneSec,
    (Timer timer) => setState(
      () {
        if (_start < 1) {
          timer.cancel();
        } else {
          _start = _start - 1;
        }
      },
    ),
  );
}

@override
void dispose() {
  _timer.cancel();
  super.dispose();
}

Widget build(BuildContext context) {
  return new Scaffold(
    appBar: AppBar(title: Text("Timer test")),
    body: Column(
      children: <Widget>[
        RaisedButton(
          onPressed: () {
            startTimer();
          },
          child: Text("start"),
        ),
        Text("$_start")
      ],
    ),
  );
}

Result :

Flutter countdown timer example

You can also use the
CountdownTimer class from the
quiver.async library, usage is even simpler :

import 'package:quiver/async.dart';

[...]

int _start = 10;
int _current = 10;

void startTimer() {
  CountdownTimer countDownTimer = new CountdownTimer(
    new Duration(seconds: _start),
    new Duration(seconds: 1),
  );

  var sub = countDownTimer.listen(null);
  sub.onData((duration) {
    setState(() { _current = _start - duration.elapsed.inSeconds; });
  });

  sub.onDone(() {
    print("Done");
    sub.cancel();
  });
}

Widget build(BuildContext context) {
  return new Scaffold(
    appBar: AppBar(title: Text("Timer test")),
    body: Column(
      children: <Widget>[
        RaisedButton(
          onPressed: () {
            startTimer();
          },
          child: Text("start"),
        ),
        Text("$_current")
      ],
    ),
  );
}

EDIT : For the question in comments about button click behavior

With the above code which uses Timer.periodic, a new timer will indeed be
started on each button click, and all these timers will update the same
_start variable, resulting in a faster decreasing counter.

There are multiple solutions to change this behavior, depending on what you
want to achieve :

  • disable the button once clicked so that the user could not disturb the countdown anymore (maybe enable it back once timer is cancelled)

  • wrap the Timer.periodic creation with a non null condition so that clicking the button multiple times has no effect

    if (_timer != null) {
    _timer = new Timer.periodic(…);
    }

  • cancel the timer and reset the countdown if you want to restart the timer on each click :

    if (_timer != null) {
    _timer.cancel();
    _start = 10;
    }
    _timer = new Timer.periodic(…);

  • if you want the button to act like a play/pause button :

    if (_timer != null) {
    _timer.cancel();
    _timer = null;
    } else {
    _timer = new Timer.periodic(…);
    }

You could also use this official async
package which provides a
RestartableTimer class which extends from Timer and adds the reset method.

So just call _timer.reset(); on each button click.

Finally, Codepen now supports Flutter ! So here is a live example so that
everyone can play with it : https://codepen.io/Yann39/pen/oNjrVOb

2020-08-13