ios - 如何在UIView中绘制贝塞尔曲线

Question

我需要在 UIView 中制作一条曲线，如下图所示。我必须使用 UIBezierPath。请帮我解决这个问题。

我还想知道如何从水平轴翻转曲线，以便在顶部有圆弧，在底部有底部。

Answer 1

要在特定的 CGSize 内绘制实心圆弧，您可以像这样定义一个 UIBezierPath:

- (UIBezierPath * _Nullable)pathOfArcWithinSize:(CGSize)size {
    if (size.width == 0 || size.height <= 0) return nil;

    CGFloat theta = M_PI - atan2(size.width / 2.0, size.height) * 2.0;
    CGFloat radius = self.bounds.size.height / (1.0 - cos(theta));

    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:CGPointMake(0, 0)];
    [path addArcWithCenter:CGPointMake(size.width / 2.0, -radius + size.height) radius:radius startAngle:M_PI_2 + theta endAngle:M_PI_2 - theta clockwise:false];
    [path closePath];

    return path;
}

这只是使用一点三角函数来计算给定 View 高度和宽度的弧的角度和半径。

一旦有了它，您就可以使用该路径构造一个 CAShapeLayer，然后将其添加为 UIView 的子层，或者您可以实现自己的 在该路径上调用 fill 的 drawRect 方法。 (或者，假设您已使用 core-graphics 对其进行标记，您也可以使用 CoreGraphics 调用执行自定义 drawRect，但我不确定您为什么要这样做。)

例如，您可以定义一个使用 CAShapeLayer 的 CurvedView 类:

//  CurvedView.h

#import <UIKit/UIKit.h>

IB_DESIGNABLE
@interface CurvedView : UIView

@property (nonatomic, strong) IBInspectable UIColor *fillColor;

@end

和

//  CurvedView.m

#import "CurvedView.h"

@interface CurvedView ()
@property (nonatomic, weak) CAShapeLayer *curvedLayer;
@end

@implementation CurvedView

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        [self configureView];
    }
    return self;
}

- (instancetype _Nullable)initWithCoder:(NSCoder *)coder {
    self = [super initWithCoder:coder];
    if (self) {
        [self configureView];
    }
    return self;
}

- (void)configureView {
    self.fillColor = [UIColor whiteColor];

    CAShapeLayer *layer = [CAShapeLayer layer];
    layer.fillColor = self.fillColor.CGColor;
    layer.strokeColor = [UIColor clearColor].CGColor;
    layer.lineWidth = 0;
    [self.layer addSublayer:layer];
    self.curvedLayer = layer;
}

- (void)setFillColor:(UIColor *)fillColor {
    _fillColor = fillColor;

    self.curvedLayer.fillColor = fillColor.CGColor;
}

- (void)layoutSubviews {
    [super layoutSubviews];

    self.curvedLayer.path = [self pathOfArcWithinSize:self.bounds.size].CGPath;
}

- (UIBezierPath * _Nullable)pathOfArcWithinSize:(CGSize)size {
    if (size.width == 0 || size.height <= 0) return nil;

    CGFloat theta = M_PI - atan2(size.width / 2.0, size.height) * 2.0;
    CGFloat radius = self.bounds.size.height / (1.0 - cos(theta));

    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:CGPointMake(0, 0)];
    [path addArcWithCenter:CGPointMake(size.width / 2.0, -radius + size.height) radius:radius startAngle:M_PI_2 + theta endAngle:M_PI_2 - theta clockwise:false];
    [path closePath];

    return path;
}

@end

产生:

或者，如果您更愿意使用 drawRect 方法而不是使用 CAShapeLayer:

//  CurvedView.m

#import "CurvedView.h"

@implementation CurvedView

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        [self configureView];
    }
    return self;
}

- (instancetype _Nullable)initWithCoder:(NSCoder *)coder {
    self = [super initWithCoder:coder];
    if (self) {
        [self configureView];
    }
    return self;
}

- (void)configureView {
    self.fillColor = [UIColor whiteColor];
}

- (void)setFillColor:(UIColor *)fillColor {
    _fillColor = fillColor;

    [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect {
    UIBezierPath *path = [self pathOfArcWithinSize:self.bounds.size];
    [self.fillColor setFill];
    [path fill];
}

- (UIBezierPath * _Nullable)pathOfArcWithinSize:(CGSize)size {
    if (size.width == 0 || size.height <= 0) return nil;

    CGFloat theta = M_PI - atan2(size.width / 2.0, size.height) * 2.0;
    CGFloat radius = self.bounds.size.height / (1.0 - cos(theta));

    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:CGPointMake(0, 0)];
    [path addArcWithCenter:CGPointMake(size.width / 2.0, -radius + size.height) radius:radius startAngle:M_PI_2 + theta endAngle:M_PI_2 - theta clockwise:false];
    [path closePath];

    return path;
}

@end

---

如果你想让圆弧占据 View 的底部，路径应该是这样的:

- (UIBezierPath * _Nullable)pathOfArcWithinSize:(CGSize)size {
    if (size.width == 0 || size.height <= 0) return nil;

    CGFloat theta = M_PI - atan2(size.width / 2.0, size.height) * 2.0;
    CGFloat radius = self.bounds.size.height / (1.0 - cos(theta));

    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:CGPointMake(0, size.height)];
    [path addArcWithCenter:CGPointMake(size.width / 2.0, radius) radius:radius startAngle:M_PI_2 * 3.0 + theta endAngle:M_PI_2 * 3.0 - theta clockwise:false];
    [path closePath];

    return path;
}

本质上，这与 theta 和 radius 相同，但从左下角开始，将 center 设置为 size。 M_PI_2 * 3.0 ± theta 的宽度/2.0、半径 和弧度: