1. 简单阴影

我们给layer设置了shadowOpacity后就能得到一个简单的阴影

view.layer.shadowOpacity = 1;

shadowOpacity设置了阴影的不透明度,取值范围在0~1
这里shadow有一个默认值
shadowOffset = CGSizeMake(0, -3)
shadowRadius = 3.0
注意:如果view没有设置背景色阴影也是不会显示的

2. 阴影属性

layer中与阴影相关的属性有以下几个

(CGColorRef *) shadowColor//阴影颜色
(float) shadowOpacity//阴影透明度
(CGSize) shadowOffset//阴影偏移量
(CGFloat) shadowRadius//模糊计算的半径
(CGPathRef *) shadowPath//阴影路径

3. shadowColor

- (void)p_setupSubViews {
    self.view.backgroundColor = [UIColor whiteColor];
    [self p_setupViewWithY:100 shadowColor:[UIColor redColor]];
    [self p_setupViewWithY:170 shadowColor:[UIColor blueColor]];
    [self p_setupViewWithY:240 shadowColor:[UIColor yellowColor]];
}

- (void)p_setupViewWithY:(CGFloat)y shadowColor:(UIColor *)shadowColor {
    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(30, y, [UIScreen mainScreen].bounds.size.width - 60, 50)];
    view.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:view];
    view.layer.shadowOpacity = 1;
    view.layer.shadowColor = shadowColor.CGColor;
}

shadow color

4. shadowOpacity

- (void)p_setupSubViews {
    self.view.backgroundColor = [UIColor whiteColor];
    [self p_setupViewWithY:100 shadowOpacity:0.2];
    [self p_setupViewWithY:170 shadowOpacity:0.6];
    [self p_setupViewWithY:240 shadowOpacity:0.9];
}

- (void)p_setupViewWithY:(CGFloat)y shadowOpacity:(float)shadowOpacity {
    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(30, y, [UIScreen mainScreen].bounds.size.width - 60, 50)];
    view.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:view];
    view.layer.shadowOpacity = shadowOpacity;
}

shadow opacity

5. shadowOffset

- (void)p_setupSubViews {
    self.view.backgroundColor = [UIColor whiteColor];
    [self p_setupViewWithY:100 shadowOffset:CGSizeMake(0, 0)];
    [self p_setupViewWithY:170 shadowOffset:CGSizeMake(5, 0)];
    [self p_setupViewWithY:240 shadowOffset:CGSizeMake(-5, 0)];
    [self p_setupViewWithY:310 shadowOffset:CGSizeMake(0, 5)];
    [self p_setupViewWithY:380 shadowOffset:CGSizeMake(0, -5)];
    [self p_setupViewWithY:450 shadowOffset:CGSizeMake(5, 5)];
    [self p_setupViewWithY:520 shadowOffset:CGSizeMake(-5, -5)];
}

- (void)p_setupViewWithY:(CGFloat)y shadowOffset:(CGSize)shadowOffset {
    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(30, y, [UIScreen mainScreen].bounds.size.width - 60, 50)];
    view.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:view];
    view.layer.shadowOpacity = 1;
    view.layer.shadowOffset = shadowOffset;
}

shadow offset

6. shadowRadius

shadowRadius其实可以理解为阴影的宽度

- (void)p_setupSubViews {
    self.view.backgroundColor = [UIColor whiteColor];
    [self p_setupViewWithY:100 shadowRadius:0];
    [self p_setupViewWithY:170 shadowRadius:3.0];
    [self p_setupViewWithY:240 shadowRadius:10.0];

}

- (void)p_setupViewWithY:(CGFloat)y shadowRadius:(CGFloat)shadowRadius {
    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(30, y, [UIScreen mainScreen].bounds.size.width - 60, 50)];
    view.backgroundColor = [UIColor yellowColor];
    [self.view addSubview:view];
    view.layer.shadowOpacity = 1;
    view.layer.shadowOffset = CGSizeMake(0, 0);
    view.layer.shadowRadius = shadowRadius;
}

shadow radius

7. shadowPath

- (void)p_setupSubViews {
    self.view.backgroundColor = [UIColor whiteColor];
    [self p_setupViewWithY1:100];
    [self p_setupViewWithY2:170];
    [self p_setupViewWithY3:240];//贝塞尔曲线未闭合
}

- (void)p_setupViewWithY1:(CGFloat)y {
    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(30, y, [UIScreen mainScreen].bounds.size.width - 60, 50)];
    view.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:view];
    view.layer.shadowOpacity = 1;
    UIBezierPath *path = [UIBezierPath bezierPathWithRect:view.bounds];
    view.layer.shadowPath = path.CGPath;
}

- (void)p_setupViewWithY2:(CGFloat)y {
    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(30, y, [UIScreen mainScreen].bounds.size.width - 60, 50)];
    view.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:view];
    view.layer.shadowOpacity = 1;
    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:CGPointMake(0, 0)];
    [path addLineToPoint:CGPointMake(0, view.frame.size.height + 10)];
    [path addLineToPoint:CGPointMake(view.frame.size.width, view.frame.size.height + 10)];
    [path addLineToPoint:CGPointMake(view.frame.size.width, 0)];
    [path addLineToPoint:CGPointMake(0, 0)];
    view.layer.shadowPath = path.CGPath;
}

- (void)p_setupViewWithY3:(CGFloat)y {
    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(30, y, [UIScreen mainScreen].bounds.size.width - 60, 50)];
    view.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:view];
    view.layer.shadowOpacity = 1;
    view.layer.shadowOffset = CGSizeMake(0, 0);
    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:CGPointMake(-5, 0)];
    [path addLineToPoint:CGPointMake(-5, view.frame.size.height)];
    [path addLineToPoint:CGPointMake(view.frame.size.width, view.frame.size.height)];
    [path addLineToPoint:CGPointMake(view.frame.size.width, 0)];
    view.layer.shadowPath = path.CGPath;
}

shadow path

当用bounds设置path时,看起来的效果与只设置了shadowOpacity一样
但是添加了shadowPath后消除了离屏渲染问题

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