今天项目遇到个需求，需要根据时间来显示不同的样式，于是去翻了一下NSCalendar，发现苹果其实是提供了这个API的

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/*
	This API reports if the date is within "today".
*/
- (BOOL)isDateInToday:(NSDate *)date NS_AVAILABLE(10_9, 8_0);
/*
	This API reports if the date is within "yesterday".
*/
- (BOOL)isDateInYesterday:(NSDate *)date NS_AVAILABLE(10_9, 8_0);

可是我们项目需要兼容到iOS7,没办法只能自己动手了因为懒，最后还是google了

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+(BOOL)isInToday:(NSDate *)date
{
    if([[NSCalendar currentCalendar] respondsToSelector:@selector(isDateInToday:)]) //iOS8以上直接使用系统api
    {
        return [[NSCalendar currentCalendar] isDateInToday:date];
    }
    else
    {
        NSCalendar *calendar = [NSCalendar currentCalendar];
        NSCalendarUnit calendarUnits = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay;
        
        NSDateComponents *components = [calendar components:calendarUnits
                                                   fromDate:date];
        NSDateComponents *todayComponents = [calendar components:calendarUnits
                                                        fromDate:[NSDate date]];
        
        NSDate *lessGranularDate1 = [calendar dateFromComponents:components];
        NSDate *lessGranularToday = [calendar dateFromComponents:todayComponents];
        
        BOOL isInToday = [lessGranularDate1 isEqualToDate:lessGranularToday];
        
        return isInToday;
    }
}
+(BOOL)isInYesterDay:(NSDate *)date
{
    if([[NSCalendar currentCalendar] respondsToSelector:@selector(isDateInYesterday:)])//iOS8以上直接使用系统api
    {
        return [[NSCalendar currentCalendar] isDateInYesterday:date];
    }
    else
    {
        NSCalendar *calendar = [NSCalendar currentCalendar];
        NSCalendarUnit calendarUnits = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay;
        
        NSDateComponents *components = [calendar components:calendarUnits
                                                   fromDate:date];
        NSDateComponents *yesterdayComponents = [calendar components:calendarUnits
                                                            fromDate:[[NSDate date] dateByAddingTimeInterval:-1*60*60*24]];
        
        NSDate *lessGranularDate1 = [calendar dateFromComponents:components];
        NSDate *lessGranularYesterday = [calendar dateFromComponents:yesterdayComponents];
        
        BOOL isYesterday = [lessGranularDate1 isEqualToDate:lessGranularYesterday];
        
        return isYesterday;
    }
}