首先，声明几个属性

@property(nonatomic,strong)UIBezierPath * beizer;@property(nonatomic,assign)CGPoint startPoint;@property(nonatomic,assign)CGPoint movePoint;@property(nonatomic,strong)CAShapeLayer * shapelayer;

然后注册屏幕上的拖拽事件，并初始化贝塞尔曲线和CAShapeLayer

- (void)viewDidLoad {    [super viewDidLoad];    UIPanGestureRecognizer * pan = [[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(panTouch:)];    [self.view addGestureRecognizer:pan];    self.beizer = [UIBezierPath bezierPath];    [self initCAShaper];}-(void)initCAShaper{    self.shapelayer = [CAShapeLayer new];    self.shapelayer.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height);    self.shapelayer.fillColor = nil;    self.shapelayer.lineCap = kCALineCapRound;    self.shapelayer.strokeColor = [UIColor cyanColor].CGColor;    self.shapelayer.lineWidth =2;    [self.view.layer addSublayer:self.shapelayer];}

紧接着处理拖拽事件

-(void)panTouch:(UIPanGestureRecognizer *)pan{    _startPoint = [pan locationInView:self.view];    if(pan.state == UIGestureRecognizerStateBegan)    {        [self.beizer moveToPoint:_startPoint];    }    if(pan.state == UIGestureRecognizerStateChanged)    {        _movePoint = [pan locationInView:self.view];        [_beizer addLineToPoint:_movePoint];        self.shapelayer.path = _beizer.CGPath;    }}

大功告成。如图