//日期轉xx前
@interface NSString(date)
+ (NSString *)dateString:(NSString *)dateStr;
@end

@implementation NSString (date)
+ (NSString *)dateString:(NSString *)dateStr
{
    NSDate *date = [NSDate dateFromString:dateStr withFormat:@"yyyy-MM-dd HH:mm:ss"];
    if (!date) {
        return @"";
    }
    int minites = [[NSDate date] timeIntervalSinceDate:date]/60;
    if (minites < 0) {
        return @"";
    }
    if (minites < 60) {//不到一小時
        return [NSString stringWithFormat:@"%d分鐘前",minites];
    }
    else if(minites < 60 * 24)//不到一天
    {
        return [NSString stringWithFormat:@"%d小時前",minites / 60];
    }
    else if(minites < 60 * 24 * 3)//不大於三天
    {
        return [NSString stringWithFormat:@"%d天前",minites / 60 / 24];
    }
    //可以根據自己需要再添加幾個月前，甚至幾年前
    return [date stringWithFormat:@"MM-dd”];//返回一個xx月xx日
}
@end