iOS－字串轉化成NSDate類型 計算與目前時間的相差 月數 天數

NSString *dateStr=[dic
objectForKey:@"date"];// 2012-05-17 11:23:23

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

    
NSUInteger unitFlags =
NSMonthCalendarUnit | NSDayCalendarUnit;  

   
NSDateFormatter *format=[[NSDateFormatter
alloc]
init];

    [format
setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

   
NSDate *fromdate=[format dateFromString:dateStr];

   
NSTimeZone *fromzone = [NSTimeZone
systemTimeZone];

   
NSInteger frominterval = [fromzone secondsFromGMTForDate: fromdate];

   
NSDate *fromDate = [fromdate  dateByAddingTimeInterval: frominterval]; 

    
NSLog(@"fromdate=%@",fromDate);

    [format
release];

   
NSDate *date = [NSDate
date];

   
NSTimeZone *zone = [NSTimeZone
systemTimeZone];

   
NSInteger interval = [zone secondsFromGMTForDate: date];

   
NSDate *localeDate = [date  dateByAddingTimeInterval: interval]; 

   
NSLog(@"enddate=%@",localeDate);

   
NSDateComponents *components = [gregorian components:unitFlags
fromDate:fromDate
toDate:localeDate options:0];  

   
NSInteger months = [components month];  

   
NSInteger days = [components day];//年[components year]

   
NSLog(@"month=%d",months);

   
NSLog(@"days=%d",days);

    [gregorian
release];

   
if (months==0&&days==0) {

        dateStr=[[dateStr
substringFromIndex:11]substringToIndex:5];

        cell.textLabel.text=[NSString
stringWithFormat:@"今天 %@",dateStr];//今天 11:23

    }else
if(months==0&&days==1){

        dateStr=[[dateStr
substringFromIndex:11]substringToIndex:5];

       
cell.textLabel.text=[NSString
stringWithFormat:@"昨天 %@",dateStr];//昨天
11:23

    }else{

        dateStr=[dateStr
substringToIndex:10];

       
cell.textLabel.text=dateStr;

    }