没有一般规则，不能给你任何时间近似值.此外，可能对您来说更重要的是系统可以为您提供多少时间用于后台获取，因为后台应用程序进入挂起状态.

There is no general rule and can not give you any time approximation. Moreover probably for you is more important how much time system can give you for a background fetch as in background app goes to suspended state.

如果我没记错的话，您可以在进入后台后请求的时间在 iOS 7 之前最多 10 分钟，在 iOS 7 上最多 180 秒，我还没有在较新版本上亲自检查过.无论如何，时间是不能保证的.

For the time you can request after going to background if I remember correctly before iOS 7 it was up to 10 minutes, on iOS 7 it was up to 180 seconds and I haven't checked it personally on newer versions. Anyway that time is not guaranteed.