tableview_nav 动画效果

-(void)scrollViewDidScroll:(UIScrollView *)scrollView

{

CGFloat yOffset  = scrollView.contentOffset.y;

CGFloat xOffset = (yOffset + BackGroupHeight)/2;

if (yOffset < -BackGroupHeight) {

CGRect rect = imageBG.frame;

rect.origin.y = yOffset;

rect.size.height =  -yOffset ;

rect.origin.x = xOffset;

rect.size.width = KScreen_Width + fabs(xOffset)*2;

imageBG.frame = rect;

}

CGFloat alpha = (yOffset+BackGroupHeight)/BackGroupHeight;

[self.navigationController.navigationBar setBackgroundImage:[self imageWithColor:[[UIColor orangeColor]colorWithAlphaComponent:alpha]] forBarMetrics:UIBarMetricsDefault];

titleLabel.alpha=alpha;

alpha=fabs(alpha);

alpha=fabs(1-alpha);

alpha=alpha<0.2? 0:alpha-0.2;

BGView.alpha=alpha;

}

- (UIImage *)imageWithColor:(UIColor *)color

{

// 描述矩形

CGRect rect = CGRectMake(0.0f, 0.0f, 1.0f, 1.0f);

// 开启位图上下文

UIGraphicsBeginImageContext(rect.size);

// 获取位图上下文

CGContextRef context = UIGraphicsGetCurrentContext();

// 使用color演示填充上下文

CGContextSetFillColorWithColor(context, [color CGColor]);

// 渲染上下文

CGContextFillRect(context, rect);

// 从上下文中获取图片

UIImage *theImage = UIGraphicsGetImageFromCurrentImageContext();

// 结束上下文

UIGraphicsEndImageContext();

return theImage;

}