1、利用NSUserDefaults来传值，这种方法只限于传少量数据的情形：

比如你要传一个float的值，在需要传的时候用
[[NSUserDefaults standardUserDefaults] setFloat:float forKey::@"float"]
接收值的时候用
[[NSUserDefaults standardUserDefaults] floatForKey:@"float"]

2、NSNotificationCenter来传值

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch * touch = [touches anyObject];
    CGPoint point = [touch locationInView:self];
    CGRect roundRect = [self rectNeedRefreshFromThisPoint:point];
    mLastPoint = CGPointMake(-1, -1);
   
    NSLog(@"%s: point(%f,%f)", __FUNCTION__, point.x, point.y);
   
    [self addToCurrentLineWithPoint:point.x y:point.y];
    [self endLine];
    [self setNeedsDisplayInRect:roundRect];
   
    NSNumber *pointX = [NSNumber numberWithFloat:point.x];
    NSNumber *pointY = [NSNumber numberWithFloat:point.y];
    NSDictionary *pointDict = [NSDictionary dictionaryWithObjectsAndKeys:pointX,@"pointX",pointY,@"pointY", nil];
    [[NSNotificationCenter defaultCenter]postNotificationName:@"passTouchedEndPointMsg"object:self userInfo:pointDict];
   
}

在消息中心的函数：

        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(getTouchedPoint:)
                                                     name:@"passTouchedEndPointMsg"
                                                   object:nil];
  

- (void) getTouchedPoint:(NSNotification *)noti
{
    NSDictionary *pointDict = [noti userInfo];
    touchedEndPointX = [[pointDict objectForKey:@"pointX"] floatValue];
    touchedEndPointY = [[pointDict objectForKey:@"pointY"] floatValue];
    NSLog(@"%f:%f",touchedEndPointX,touchedEndPointY);
}

用消息来传参数有下面几点说法：object指的是发送者、在poseter端的userInfo里面可以存放要传的参数，必须为NSDictionary类型。在center端获取这个dictionary类型用:[notification userInfo];来获取