二个时间字符串比较

//比较时间
-(void)initTimerCompare
{
    
    NSString *starTimer=@"2014-08-29";
    NSString *finishTimer=@"2014-09-30";
    
    BOOL result = [starTimer compare:finishTimer] == NSOrderedSame;
    NSLog(@"result:%d",result);
    if (result==1) {
        UIAlertView *alert=[[UIAlertView alloc]initWithTitle:nil message:@"开始时间和结束时间相等" delegate:self cancelButtonTitle:@"知道了" otherButtonTitles:nil, nil];
        [alert show];
        return;
    }
    
    BOOL result1 = [starTimer compare:finishTimer]==NSOrderedDescending;
    NSLog(@"result1:%d",result1);
    if (result1==1) {
        UIAlertView *alert=[[UIAlertView alloc]initWithTitle:nil message:@"开始时间晚于结束时间" delegate:self cancelButtonTitle:@"知道了" otherButtonTitles:nil, nil];
        [alert show];
        return;
    }

    
    BOOL result2 = [starTimer compare:finishTimer]==NSOrderedAscending;
    NSLog(@"result2:%d",result1);
    if (result2==1) {
        UIAlertView *alert=[[UIAlertView alloc]initWithTitle:nil message:@"开始时间早于结束时间" delegate:self cancelButtonTitle:@"知道了" otherButtonTitles:nil, nil];
        [alert show];
        return;
    }

}