UIBezierPath主要用来绘制矢量图形，它是基于Core Graphics对CGPathRef数据类型和path绘图属性的一个封装，所以是需要图形上下文的（CGContextRef），所以一般UIBezierPath在drawRect中使用。

直接画个圆吧！

创建一个CustonView继承自UIView
#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface CustonView : UIView

/// 进度（值范围0.0~1.0，默认0.0）
@property (nonatomic, assign) CGFloat progress;

@end

NS_ASSUME_NONNULL_END

在.m文件重写
- (void)drawRect:(CGRect)rect {
    UIBezierPath *path = [UIBezierPath bezierPathWithArcCenter:CGPointMake(self.bounds.size.width/2.f,self.bounds.size.height/2.f)radius:self.bounds.size.width/2.f startAngle:0 endAngle:M_PI *2*self.progress clockwise:YES];
    //创建一个shapeLayer
    CAShapeLayer *layer = [CAShapeLayer layer];
    layer.frame = self.bounds;
    layer.path = path.CGPath;                         //从bezier曲线获取到的形状
    layer.strokeColor = [UIColor greenColor].CGColor; //边缘线的颜色
    layer.fillColor = [UIColor clearColor].CGColor;   //闭环填充的颜色
    layer.lineCap = kCALineCapSquare;                  //边缘线的类型
    layer.lineWidth = 4.0f;                            //线条宽度
    //    layer.strokeStart = 0.0f;
    //    layer.strokeEnd = 0.0f;
    //    self.layer.mask = layer;
    //    [path stroke];
    //    //将layer添加进图层
    [self.layer addSublayer:layer];
}

- (void)setProgress:(CGFloat)progress {
    _progress = progress;
    [self setNeedsDisplay];
}

使用
#import "CustonView.h"

@interface xxxxxxVC ()

@property (nonatomic , strong)NSTimer *timer;
@property (nonatomic , assign)float index;
@property (nonatomic , strong)CustonView *showView;
@end

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
   [self LayerTest];
    self.view.backgroundColor = [UIColor whiteColor];
    self.index = 0.01;
    self.timer = [NSTimer timerWithTimeInterval:0.1 target:self selector:@selector(timerEvent) userInfo:nil 
 repeats:YES];
    [[NSRunLoop mainRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];
}

- (void)timerEvent {
    self.index+=0.01;
    NSLog(@"%f",self.index);
    if (self.index >=1) {
        [self.timer invalidate];
        self.timer = nil;
    }
    self.showView.progress = self.index;
}

#pragma mark --- CALayer
- (void)LayerTest {
    self.showView = [[CustonView alloc] initWithFrame:CGRectMake(100,200, 100, 100)];
    self.showView.backgroundColor = [UIColor whiteColor];
    self.showView.alpha =0.5;
    [self.view addSubview:self.showView];
}