dart - 链式 future 不按顺序执行

Question

我目前正在从蓝牙设备读取变量。这显然会花费不确定的时间，所以我正在使用 future (此方法在我下面的代码中为 readCharacteristic)。

一次不能进行多个读取操作 - 如果在第一个操作仍在进行时启动第二个读取操作，Flutter 将抛出错误。

我的理解是，使用 .then() 将 futures 链接在一起只会允许下一个语句在前一个调用完成时执行。这个想法似乎是正确的，直到我尝试读取第三个值 - 即由于重叠的读取事件而引发错误。

这是我的代码:

readCharacteristic(scanDurationCharacteristic)
    .then((list) => sensorScanDuration = list[0].toDouble())
    .then((_) {
  readCharacteristic(scanPeriodCharacteristic)
      .then((list) => sensorScanPeriod = list[0].toDouble());
}).then((_) {
  readCharacteristic(aggregateCharacteristic)
      .then((list) => sensorAggregateCount = list[0].toDouble());
}).then((_) {
  readCharacteristic(appEUICharacteristic)
      .then((list) => appEUI = decimalToHexString(list));
}).then((_) {
  readCharacteristic(devEUICharacteristic)
      .then((list) => devEUI = decimalToHexString(list));
}).then((_) {
  readCharacteristic(appKeyCharacteristic)
      .then((list) => appKey = decimalToHexString(list));
});

有什么更好的方法来确保这些读取事件不会重叠？

Answer 1

尽管 R.C Howell 的回答是正确的，但更喜欢使用 async/await 关键字来代替。这更具可读性，您犯错的可能性也较小

Future<void> scanBluetooth() async {
  sensorScanDuration = (await readCharacteristic(scanDurationCharacteristic))[0].toDouble();
  sensorScanPeriod = (await readCharacteristic(scanPeriodCharacteristic))[0].toDouble();
  sensorAggregateCount = (await readCharacteristic(aggregateCharacteristic))[0].toDouble();
  appEUI = await readCharacteristic(appEUICharacteristic).then(decimalToHexString);
  devEUI = await readCharacteristic(devEUICharacteristic).then(decimalToHexString);
  appKey = await readCharacteristic(appKeyCharacteristic).then(decimalToHexString);
}