步骤：
1、新建UIBezierPath对象bezierPath
2、新建CAShapeLayer对象caShapeLayer
3、将bezierPath的CGPath赋值给caShapeLayer的path，即caShapeLayer.path = bezierPath.CGPath
4、把caShapeLayer添加到某个显示该图形的layer中

下面的小例子是一个环形的progress代码，有具体的使用方法
.h文件：

#import <QuartzCore/QuartzCore.h>
#import <UIKit/UIKit.h>

@interface KACircleProgressView : UIView {
    CAShapeLayer *_trackLayer;
    UIBezierPath *_trackPath;
    CAShapeLayer *_progressLayer;
    UIBezierPath *_progressPath;
}

@property (nonatomic, strong) UIColor *trackColor;
@property (nonatomic, strong) UIColor *progressColor;
@property (nonatomic) float progress;//0~1之间的数
@property (nonatomic) float progressWidth;

- (void)setProgress:(float)progress animated:(BOOL)animated;

@end

.m文件：

#import "KACircleProgressView.h"

@implementation KACircleProgressView

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
        _trackLayer = [CAShapeLayer new];
        [self.layer addSublayer:_trackLayer];
        _trackLayer.fillColor = nil;
        _trackLayer.frame = self.bounds;
        
        _progressLayer = [CAShapeLayer new];
        [self.layer addSublayer:_progressLayer];
        _progressLayer.fillColor = nil;
        _progressLayer.lineCap = kCALineCapRound;
        _progressLayer.frame = self.bounds;
        
        //默认5
        self.progressWidth = 5;
    }
    return self;
}

- (void)setTrack
{
    _trackPath = [UIBezierPath bezierPathWithArcCenter:self.center radius:(self.bounds.size.width - _progressWidth)/ 2 startAngle:0 endAngle:M_PI * 2 clockwise:YES];;
    _trackLayer.path = _trackPath.CGPath;
}

- (void)setProgress
{
    _progressPath = [UIBezierPath bezierPathWithArcCenter:self.center radius:(self.bounds.size.width - _progressWidth)/ 2 startAngle:- M_PI_2 endAngle:(M_PI * 2) * _progress - M_PI_2 clockwise:YES];
    _progressLayer.path = _progressPath.CGPath;
}

- (void)setProgressWidth:(float)progressWidth
{
    _progressWidth = progressWidth;
    _trackLayer.lineWidth = _progressWidth;
    _progressLayer.lineWidth = _progressWidth;
    
    [self setTrack];
    [self setProgress];
}

- (void)setTrackColor:(UIColor *)trackColor
{
    _trackLayer.strokeColor = trackColor.CGColor;
}

- (void)setProgressColor:(UIColor *)progressColor
{
    _progressLayer.strokeColor = progressColor.CGColor;
}

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

- (void)setProgress:(float)progress animated:(BOOL)animated
{
    
}

/*
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
    // Drawing code
}
*/
@end

使用：

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    KACircleProgressView *progress = [[KACircleProgressView alloc] initWithFrame:CGRectMake(20, 40, 100, 100)];
    [self.view addSubview:progress];
    progress.trackColor = [UIColor blackColor];
    progress.progressColor = [UIColor orangeColor];
    progress.progress = 0.7;//progress所占比例
    progress.progressWidth = 10;//图形圆的粗细
}

效果图：

效果图.png

来自：http://blog.csdn.net/volcan1987/article/details/9969455