问题
I have to setting a time to check for update data from server 2times a day, suppose 9AM and 9PM, but i don't know the way to do that.
Create a thread, run every-time and check time current time with setting,if they are equal,so do task? This way is good? I think that's bad performance.
回答1:
Use thread but instead of checking every sec, if it is equal. You could use NSNotification. When the time is the same, it will send a notification to get the data.
You can read this: iOS timed background processing
Can go through this tutorial as well: http://mobile.tutsplus.com/tutorials/iphone/ios-multitasking-local-notifications/
I have reading up as well. Something new for me as well. Best is NSLocalNotifications. Have a look at this: Reminder App
The documentation for Local Notifications: Local Notifications
回答2:
maybe when your app is launching , you can get the current time(also can get the timeInterval of current time called timeInterval0) using [NSDate date] and if your current time < 9:00AM today , you can get the timeInterval of 9:00AM today called timeInterval1. and then you can get how many seconds between now and your target time , then use NSTimer to invocation your method ,the delay is the between seconds.
In your method , you can check the update , and you must also to calc the seconds from then between next 9:00 as above.
来源：https://stackoverflow.com/questions/14475195/how-to-create-thread-to-checking-time