自定义带弹性效果的pageControl

分三部分实现，在drawrect方法里画出灰色背景，根据pageCount创建对应个数的dotView放置在对应位置，并隐藏，创建一个CAShapeView类型的layer，根据scrollView的偏移量 构建贝塞尔曲线，画出红色线条，以及形变的大圆。

大圆的形变以及构建思路：

（图引用自：http://kittenyang.com/deformationandgooey/）

下面就是构建A、B、C、D、c1、c2、c3、c4、c5、c6、c7、c8这些点，给A、B、C、D、四个点，一个关于contentOffset的形变量，以达到园形变的效果。value ＝ （半径 ＊ 比例）＊形变因素，其中形变因素于contentOffset相关（在滑动一个页面时会形成这样的关系：0～0.5～0）；CGFloat factor = MIN(0.5, MAX(0, (ABS(scrollView.contentOffset.x - last) / scrollView.frame.size.width)));，构建好点后，根据偏移量，更新点的坐标，生成新的贝塞尔曲线，便生成形变的 圆了。

下面是部分代码：

/** 根据scrollView 更新贝塞尔曲线 */
- (void)updateDotLayerScrollView:(UIScrollView *)scrollView{
    // 判断滑动方向
    BOOL left = (scrollView.contentOffset.x - self.lastOffsetX) >= 0?YES:NO;
    
    // 向左滑动就显示dotView
    if (left) {
        [self setDotViewShowWithScrollView:scrollView];
    }
    
    CGPoint dotCenter = [self calculateDotCenterWithScrollView:scrollView];
    
    // 计算当前偏移量的 归属地（超过一半 就归属后者，反之前者）
    int count = (int)(scrollView.contentOffset.x / scrollView.frame.size.width+0.5);
    
    // 根据count 计算归属地 的偏移量
    CGFloat last = scrollView.frame.size.width * count;
    
    CGFloat factor = MIN(0.5, MAX(0, (ABS(scrollView.contentOffset.x - last) / scrollView.frame.size.width)));
    
    // extra 是 A、B、C、D四点的 位移量，跟factor有关。而factor跟contentOffset相关，其关系为0～0.5～0；
    CGFloat extra = self.SeletedDotRadiu * 4 / 5 * factor;
    
    // 构成贝塞尔曲线的相关点 的计算
    A = CGPointMake(dotCenter.x, dotCenter.y - self.SeletedDotRadiu+extra);
    B = CGPointMake(left?(dotCenter.x+self.SeletedDotRadiu):(dotCenter.x+self.SeletedDotRadiu+extra * 2), dotCenter.y);
    C = CGPointMake(dotCenter.x, dotCenter.y+self.SeletedDotRadiu-extra);
    D = CGPointMake(left?(dotCenter.x-self.SeletedDotRadiu-extra*2):(dotCenter.x-self.SeletedDotRadiu), dotCenter.y);
    // 1.8 的得来应该是能计算出来的，不过不知道咋算，试出来
    CGFloat offset = self.SeletedDotRadiu / 1.8;
    
    c1 = CGPointMake(A.x + offset, A.y);
    c2 = CGPointMake(B.x, B.y - offset);
    c3 = CGPointMake(B.x, B.y + offset);
    c4 = CGPointMake(C.x + offset, C.y);
    c5 = CGPointMake(C.x - offset, C.y);
    c6 = CGPointMake(D.x, D.y + offset);
    c7 = CGPointMake(D.x, D.y - offset);
    c8 = CGPointMake(A.x - offset, A.y);
    
    UIBezierPath* ovalPath = [UIBezierPath bezierPath];
    CGPoint startPoint = CGPointMake(self.SeletedDotRadiu, CGRectGetHeight(self.frame) / 2.0);
    [ovalPath moveToPoint: startPoint];
    [ovalPath addLineToPoint:D];
    [ovalPath addCurveToPoint:C controlPoint1:c6 controlPoint2:c5];
    [ovalPath addCurveToPoint:B controlPoint1:c4 controlPoint2:c3];
    [ovalPath addCurveToPoint:A controlPoint1:c2 controlPoint2:c1];
    [ovalPath addCurveToPoint:D controlPoint1:c8 controlPoint2:c7];
    
    [ovalPath closePath];
    self.dotLayer.path = ovalPath.CGPath;
    
    self.lastOffsetX = scrollView.contentOffset.x;
}

    drawRect 方法：

/** 画初始 的背景 */
- (void)drawRect:(CGRect)rect {
    
    // 控件垂直方向中心
    CGFloat verticalCenter = rect.size.height / 2.0;
    // 圆点 半径
    CGFloat dotR = self.dotRadiu;
    
    // 选中圆点 半径
    CGFloat selectedDotR = self.SeletedDotRadiu;
    // 圆心距离
    CGFloat distanceCenter = (rect.size.width - 2 * selectedDotR) / (self.pageCount - 1);
    
    UIBezierPath *path = [UIBezierPath bezierPathWithRect:CGRectMake(selectedDotR, (rect.size.height - self.lineWidth) / 2.0, rect.size.width - 2 * selectedDotR, self.lineWidth)];
    
    [self.color setFill];

    for (int i = 0; i < self.pageCount; i++) {
        
        UIBezierPath *dotPath = [UIBezierPath bezierPathWithArcCenter:CGPointMake(selectedDotR + distanceCenter * i, verticalCenter) radius:dotR startAngle:0 endAngle:M_PI * 2 clockwise:YES];
        [path appendPath:dotPath];
    }
    [path fill];
    
}

完整代码：http://pan.baidu.com/s/1i4y78gt