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。

我也想知道如何从水平轴翻转曲线，这样我的圆弧在顶部，底部在底部。

Answer 1

要在特定 CGSize 内绘制实心圆弧，您可以像这样定义 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视图的高度和宽度的弧的角度和半径。

一旦你有了它，你可以使用该路径构建一个 CAShapeLayer，然后将其添加为 UIView 的子层，或者你可以实现你自己的 drawRect 方法在该路径上调用 fill。（或者，假设您已使用 core-graphics 标记它，您也可以使用 CoreGraphics 调用进行自定义 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 class

//  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视图的底部，路径看起来像：

- (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，theta和radius是一样的，只是从左下角开始，将center设置为size.width / 2.0, radius，弧从M_PI_2 * 3.0 ± theta:

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