How to translate a NSString object to NSDate quickly?

I try to get NSDate objects from NSString which I get from sqlite, but there is a time problem. I takes me 130ms every time.开发者_如何学C And it's insufferable for i have two hundred objects to deal with. So can somebody tell me what i should do. Thanks.

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Assuming you're using NSDateFormatter, you should attend to Apple's recommendation, caching formatters for efficiency. Instead of creating a NSDateFormatter each time you want to convert a date, you should keep a single instance of your NSDateFormatter. From Data Formatting guide:

Cache Formatters for Efficiency

Creating a date formatter is not a cheap operation. If you are likely to use a formatter frequently, it is typically more efficient to cache a single instance than to create and dispose of multiple instances. One approach is to use a static variable.

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    NSDateFormatter *formatter=[[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"HH:mm:ss:SSS"];
     NSDate *currentdate=[formatter dateFromString:currentdateStr];
 //it returns DateObject If String in Specified Format otherwise Returns nil;

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I think this code block will help you :

        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
        [dateFormatter setDateFormat:@"<Add Your Date Format>"];

        NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

        NSDateComponents *dateComponent = [calendar components:NSYearCalendarUnit
                                        |NSMonthCalendarUnit
                                        |NSDayCalendarUnit 
                                        fromDate:[dateFormatter dateFromString: <Add Your Date String> ]];

        [dateComponent setHour:24];
        [dateComponent setMinute:00];
        [dateComponent setSecond:00];

        <Your NSDate Object> = [calendar dateFromComponents:dateComponent];

It might require to change dateComponent values for Hour, Minute, Seconds - according to your calendar time.

Let me know if you face any problem in this..