比较两个日期的大小

//比较两个日期的大小  日期格式为2016-08-14 08：46：20

+ (NSInteger)compareDate:(NSString*)aDate withDate:(NSString*)bDate

{

NSInteger aa;

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

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

NSDate *dta = [[NSDate alloc] init];

NSDate *dtb = [[NSDate alloc] init];

dta = [dateformater dateFromString:aDate];

dtb = [dateformater dateFromString:bDate];

NSComparisonResult result = [dta compare:dtb];

if (result=NSOrderedSame)

{

//        相等  aa=0

}else if (result=NSOrderedAscending)

{

//bDate比aDate大

aa=1

}else if (result=NSOrderedDescending)

{

//bDate比aDate小

aa=-1

}

return aa;

}