Decrease time in objective-c

I have a number of hours and a number of minutes, and I want a reduce the time of 1 second. So, I think I must create a nsdate object with my time, and after find the method to decrease the time. I looked in the apple docume开发者_如何学Pythonntation but I don't find how to do this.

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You can use this

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"MM/dd/yyyy"];
NewDateString = [formatter stringFromDate:[NSDate dateWithTimeIntervalSinceNow:-1]

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You want NSDateComponents. Note, you need to use it with a specific calendar. A code example is listed on the page to which I linked.

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Don't reinvent the wheel. There are many open source NSDate additions that you can use here. See here