我建议使用调度组：
func resetDevice(completion: () -> ()) {
let dispatchGroup = DispatchGroup()
for device in devices {
dispatchGroup.enter()
device.isValid = 0
DeviceManager.instance.updateDevice(device).call { response in
print("device reset")
dispatchGroup.leave()
}
}
dispatchGroup.notify(queue: DispatchQueue.main) {
// Some code to execute when all devices have been reset
}
}
每个设备都立即进入该组，但直到收到响应后才离开该组。在所有对象都离开组之前，不会调用最后的notify块。
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