iOS绘图及贝塞尔曲线关键知识

一、如果是自定义一个继承于UIView的子类要在这个子类view上画图的话：1.假如是在drawRect：方法中单纯地画贝塞尔曲线 

- (void)set;

- (void)setFill;

- (void)setStroke;

这三个方法是用来设置这种画线方式所需的边色或者填充色（是类UIColor的实例方法）UIBezierPath *path = [UIBezierPath bezierPath];

[path stroke];//这个方法必须要写的,否则不会画出来（描边）

[path fill];//这个也要写，否则不会画线（填充）

2.假如画完线之后（不论是否在drawRect：方法中），所画贝塞尔曲线的CGPath属性是用作CAShapeLayer的path属性的那么[path stroke]、[path fill]这两个方法可以不要，（1）如果非要写的话画线的代码需要放到

UIGraphicsBeginImageContext(self.view.bounds.size);

UIGraphicsEndImageContext();

这两句代码之间才能避免控制台打印出一串

“Jul  6 14:32:00  TextBeiSaiEr[7433]: CGContextSaveGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Jul  6 14:32:00  TextBeiSaiEr[7433]: CGContextSetLineWidth: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Jul  6 14:32:00  TextBeiSaiEr[7433]: CGContextSetLineJoin: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Jul  6 14:32:00  TextBeiSaiEr[7433]: CGContextSetLineCap: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Jul  6 14:32:00  TextBeiSaiEr[7433]: CGContextSetMiterLimit: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Jul  6 14:32:00  TextBeiSaiEr[7433]: CGContextSetFlatness: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Jul  6 14:32:00  TextBeiSaiEr[7433]: CGContextAddPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Jul  6 14:32:00  TextBeiSaiEr[7433]: CGContextDrawPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Jul  6 14:32:00  TextBeiSaiEr[7433]: CGContextRestoreGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

”

这些警告。

如果在这两句代码之间用

CGContextRef contextRef =UIGraphicsGetCurrentContext();

CGContextAddEllipseInRect(contextRef, CGRectMake(0,0,100,100));

CGContextSetFillColorWithColor(contextRef,  [UIColor blueColor].CGColor);

 CGContextFillPath(contextRef);

来画线的话，下面这句代码是必须的

UIImage* image = UIGraphicsGetImageFromCurrentImageContext();

（2）如果不写[path stroke]、[path fill]这两个方法的话

UIGraphicsBeginImageContext(self.view.bounds.size);

UIGraphicsEndImageContext();

这两句代码也可以不需要

二、如果不自定义UIView的子类

可以直接按一中的第2点来处理

代码如下：（写在viewDidLoad方法中的）

UIBezierPath* path = [UIBezierPath bezierPath];

path.lineWidth =3.0;

path.lineCapStyle =kCGLineCapRound;//终点样式

path.lineJoinStyle =kCGLineJoinRound;//连接点样式

[path moveToPoint:CGPointMake(100,20)];//起点

[path addLineToPoint:CGPointMake(200,40)];//途经点

[path addLineToPoint:CGPointMake(160,140)];//途经点

[path addLineToPoint:CGPointMake(40,140)];//途经点

[path addLineToPoint:CGPointMake(0,40)];//途经点

[path closePath];//闭合

CAShapeLayer * layer = [CAShapeLayer layer];

layer.path = path.CGPath;

layer.backgroundColor = [UIColor clearColor].CGColor;

layer.fillColor = [UIColor clearColor].CGColor;

layer.lineCap =kCALineCapRound;

layer.lineJoin =kCALineJoinRound;

layer.strokeColor = [UIColor redColor].CGColor;

layer.lineWidth = path.lineWidth;

self.view.layer.shouldRasterize = YES;//去线条锯齿

[self.view.layer addSublayer:layer];