本文所需知识点:

1 UIBezierPath画线
2 高中三角函数基础知识,包括正弦函数,余弦函数,反正弦函数,反余弦函数,圆的参数方程等

温馨提示:

1 凑热闹的直接复制代码,直接代码拿走;
2 想研究的可以逐行看一下什么意思,每一行都不能去掉
3 有问题欢迎留言,不吝赐教

示意图奉上:

image.png

废话不多说,直接上代码:

FiveStarView.h

#import <UIKit/UIKit.h>
    @interface FiveStarView : UIView
    //五角星的中心点坐标
    @property (nonatomic, assign) CGPoint centerPoint;

    /**
     五角星一个角的坐标
     */
    @property (nonatomic, assign) CGPoint aCorner;

    /**
     给一个范围画一个最大的五角星,不能超出本视图大小
     * 如果设置了这个属性,aCorner和centerPoint将失去效果
     * 如果aCorner和centerPoint也没有设置,将会有一个默认的位置和大小
     
     */
    @property (nonatomic, assign) CGRect contentRect;

    @end

FiveStarView.m

#import "FiveStarView.h"

    @implementation FiveStarView
    // Only override drawRect: if you perform custom drawing.
    // An empty implementation adversely affects performance during animation.
    - (void)drawRect:(CGRect)rect {
        CGPoint point1 = CGPointZero;
        CGPoint center = CGPointZero;
        if(self.contentRect.size.height != 0){
            rect = self.contentRect;
            point1 = CGPointMake(rect.origin.x, rect.origin.y+rect.size.height/2.0);
            center = CGPointMake(rect.origin.x+rect.size.height/2.0, rect.origin.y+rect.size.height/2.0);
        } else if (self.centerPoint.x != 0 && self.centerPoint.y != 0 && self.aCorner.x != 0 && self.aCorner.y != 0){
            point1 = self.aCorner;
            center = self.centerPoint;
        }else{//默认
        //设五角星一点坐标
    //    CGPoint point1 = CGPointMake(10, 40);
    //    CGPoint point1 = CGPointMake(10, 10);
    //    CGPoint point1 = CGPointMake(40, 40);
    //    point1 = CGPointMake(rect.size.width, rect.size.height/2.0);//右侧中点
    //        point1 = CGPointMake(0, rect.size.height/2.0);//左侧中点
    //        point1 = CGPointMake(rect.size.width/2, rect.size.height);//底部侧中点
            point1 = CGPointMake(rect.size.width/2, 0);//顶部中点
        center = CGPointMake(rect.size.width/2.0, rect.size.height/2.0);
        }
        
        //计算圆半径
        CGFloat r = sqrt((center.x-point1.x)*(center.x-point1.x) + (center.y-point1.y)*(center.y-point1.y));
        //首先判断五角星所在圆是否在view内
    //    if([self roundIfOutRectWithCenter:center r:r rect:rect]){//超出边界不在画五角星
        NSAssert([self roundIfOutRectWithCenter:center r:r rect:rect] == NO, @"超出边界不再画五角星");
    //        return;
    //    }
        
        //角度alpha
        CGFloat alpha = asin((point1.y-center.y)/r);
        CGFloat alpha1 = acos((point1.x-center.x)/r);
        CGPoint point2 = CGPointZero;
        CGPoint point3 = CGPointZero;
        CGPoint point4 = CGPointZero;
        CGPoint point5 = CGPointZero;
        //这个是因为asin函数的象限决定的,反函数出来的角度不一定是真是的角度,所以有以下处理
        if (point1.x < center.x && point1.y == center.y) {
            alpha = alpha1;
        }else if (point1.x > center.x && point1.y == center.y){
            
        }else if(point1.x < center.x && point1.y < center.y){
            alpha = -1 *alpha + M_PI;
        }else if (point1.x < center.x && point1.y > center.y){
            alpha = alpha1;
        }

        point2 = CGPointMake(r*cos(alpha+72.0/180.0*M_PI)+center.x, r*sin(alpha+72.0/180.0*M_PI)+center.y);
            
        point3 = CGPointMake(r*cos(alpha+72.0*2/180.0*M_PI)+center.x, r*sin(alpha+72.0*2/180.0*M_PI)+center.y);
        point4 = CGPointMake(r*cos(alpha+72.0*3/180.0*M_PI)+center.x, r*sin(alpha+72.0*3/180.0*M_PI)+center.y);
        point5 = CGPointMake(r*cos(alpha+72.0*4/180.0*M_PI)+center.x, r*sin(alpha+72.0*4/180.0*M_PI)+center.y);
        UIBezierPath *path = [UIBezierPath bezierPathWithRect:rect];
        [path moveToPoint:point1];
        [path addLineToPoint:point3];
        [path addLineToPoint:point5];
        [path addLineToPoint:point2];
        [path addLineToPoint:point4];
        [path addLineToPoint:point1];
        [[UIColor redColor] setStroke];
        [path stroke];
        
    //    UIBezierPath *p = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(30-r, 30-r, r*2, r*2) cornerRadius:r];
    //    [p stroke];
        
        
        
    }
    -(BOOL)roundIfOutRectWithCenter:(CGPoint)center r:(CGFloat)r rect:(CGRect)rect{
        CGFloat width = rect.size.width;
        CGFloat height = rect.size.height;
        CGPoint point1 =CGPointMake(width, center.y);
        CGPoint point2 =CGPointMake(0, center.y);
        CGPoint point3 =CGPointMake(center.x, height);
        CGPoint point4 =CGPointMake(0, height);
        
        if ([self isBiggerThan:r dis:[self distanceWith:point1 point:center]] &&
            [self isBiggerThan:r dis:[self distanceWith:point2 point:center]] &&
            [self isBiggerThan:r dis:[self distanceWith:point3 point:center]] &&
            [self isBiggerThan:r dis:[self distanceWith:point4 point:center]]) {
            return NO;
        }
        return YES;
    }
    -(CGFloat)distanceWith:(CGPoint)point1 point:(CGPoint)point2{
        return sqrt((point1.x-point2.x) * (point1.x-point2.x) + (point1.y-point2.y)*(point1.y-point2.y));
    }
    - (BOOL)isBiggerThan:(CGFloat)r dis:(CGFloat)distace{
        if (distace >= r) {
            return YES;
        }else{
            return NO;
        }
    }
    @end