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绘制一条直线

- (void)drawRect:(CGRect)rect {    // Drawing code    CGContextRef ctx = UIGraphicsGetCurrentContext();    CGMutablePathRef path = CGPathCreateMutable();    CGPathMoveToPoint(path, NULL, CGRectGetMinX(rect), CGRectGetMinY(rect));    CGPathAddLineToPoint(path, NULL, CGRectGetMaxX(rect), CGRectGetMaxY(rect));    CGPathCloseSubpath(path);    CGContextAddPath(ctx, path);    CGContextSetStrokeColorWithColor(ctx, [UIColor blueColor].CGColor);    CGContextStrokePath(ctx);    CGPathRelease(path);}

结果如下：

- (void)drawRect:(CGRect)rect {    // Drawing code    CGContextRef context = UIGraphicsGetCurrentContext();    CGMutablePathRef path = CGPathCreateMutable();    CGPathMoveToPoint(path, NULL, 50, 50);    CGPathAddLineToPoint(path, NULL, 200, 200);    CGPathRef thickPath = CGPathCreateCopyByStrokingPath(path, NULL, 10, kCGLineCapButt, kCGLineJoinBevel, 0);    CGContextAddPath(context, thickPath);    CGContextSetStrokeColorWithColor(context, [UIColor blackColor].CGColor);    CGContextSetFillColorWithColor(context, [UIColor blueColor].CGColor);    CGContextSetLineWidth(context, 3);    CGContextDrawPath(context, kCGPathFillStroke);    CGPathRelease(thickPath);    CGPathRelease(path);}

绘制圆弧

请参考

- (void)drawRect:(CGRect)rect {    // Drawing code    CGContextRef context = UIGraphicsGetCurrentContext();    //创建transform    CGAffineTransform transform = CGAffineTransformMakeTranslation(50, 50);    CGMutablePathRef path = CGPathCreateMutable();    //圆弧    CGPathAddArc(path, &transform, 50, 50, 50, 0, 1.5 * M_PI, NO);    //划线    CGPathMoveToPoint(path, &transform, 50, 0);    CGPathAddLineToPoint(path, &transform, 50, 50);    CGPathAddLineToPoint(path, &transform, 100, 50);    //将CGMutablePathRef添加到当前Context内    CGContextAddPath(context, path);    [[UIColor grayColor] setFill];    [[UIColor blueColor] setStroke];    CGContextSetLineWidth(context, 2);    CGContextDrawPath(context, kCGPathFillStroke);    CGPathRelease(path);}

使用CGPathAddArcToPoint

- (void)drawRect:(CGRect)rect {    // Drawing code    CGContextRef context = UIGraphicsGetCurrentContext();    //创建用于转移坐标的Transform，这样我们不用按照实际显示做坐标计算    CGAffineTransform transform = CGAffineTransformMakeTranslation(50, 50);    //创建CGMutablePathRef    CGMutablePathRef path = CGPathCreateMutable();    //半径为30    CGFloat radius = 30;    //初始点为(0, 0)    CGPathMoveToPoint(path, &transform, 0, 0);    //右上角和右下角两个点，画出半个圆角    CGPathAddArcToPoint(path, &transform, 100, 0, 100, 100, radius);    //右下角和左下角两个点，画出另外半个圆角    CGPathAddArcToPoint(path, &transform, 100, 100, 0, 100, radius);    //CGPathAddArcToPoint会在交点中停止，所以需要再次调用CGPathAddLineToPoint画出下面的线    CGPathAddLineToPoint(path, &transform, 0, 100);    //将CGMutablePathRef添加到当前Context内    CGContextAddPath(context, path);    [[UIColor grayColor] setFill];    [[UIColor blueColor] setStroke];    CGContextSetLineWidth(context, 2);    CGContextDrawPath(context, kCGPathFillStroke);    CGPathRelease(path);}

CGPathRef上绘制渐变颜色

在iOS Core Graphics中绘制渐变颜色主要是通过使用CGContextDraw(xxx)Gradient相关函数，比如，常见的线性渐变就是CGContextDrawLinearGradient函数，这里帖子封装了绘制渐变颜色的具体代码过程，我们拿过来直接用，只不过原帖代码是用CGContextAddRect画了一个矩形，我们改一下去画CGPathRef。这里无论是什么形状其实无所谓，原理都是用来做Clip，所以需要在CGContextClip函数前调用CGContextAddPath函数把CGPathRef加入到Context中。

另外一个需要注意的地方是渐变的方向，方向是由两个点控制的，点的单位就是坐标。因此需要正确从CGPathRef中找到正确的点，方法当然有很多种看具体实现，本例中，我就是简单得通过调用CGPathGetBoundingBox函数，返回CGPathRef的矩形区域，然后根据这个矩形取两个点，读者可以根据自行需求修改具体代码。

OK，把代码封装成一个方法，类似这样：

/** * 修改自http://www.raywenderlich.com/32283/core-graphics-tutorial-lines-rectangles-and-gradients */- (void)drawLinearGradient:(CGContextRef)context                      path:(CGPathRef)path                startColor:(CGColorRef)startColor                  endColor:(CGColorRef)endColor{    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();    CGFloat locations[] = { 0.0, 1.0 };    NSArray *colors = @[(__bridge id) startColor, (__bridge id) endColor];    CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef) colors, locations);    CGRect pathRect = CGPathGetBoundingBox(path);    //具体方向可根据需求修改    CGPoint startPoint = CGPointMake(CGRectGetMidX(pathRect), CGRectGetMinY(pathRect));    CGPoint endPoint = CGPointMake(CGRectGetMidX(pathRect), CGRectGetMaxY(pathRect));    CGContextSaveGState(context);    CGContextAddPath(context, path);    CGContextClip(context);    CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0);    CGContextRestoreGState(context);    CGGradientRelease(gradient);    CGColorSpaceRelease(colorSpace);}

接下来就可以使用了，示例代码：

- (void)viewDidLoad {    [super viewDidLoad];    //创建CGContextRef    UIGraphicsBeginImageContext(self.view.bounds.size);    CGContextRef gc = UIGraphicsGetCurrentContext();    //创建CGMutablePathRef    CGMutablePathRef path = CGPathCreateMutable();    //绘制Path    CGRect rect = CGRectInset(self.view.bounds, 30, 30);    CGPathMoveToPoint(path, NULL, CGRectGetMinX(rect), CGRectGetMinY(rect));    CGPathAddLineToPoint(path, NULL, CGRectGetMidX(rect), CGRectGetHeight(rect));    CGPathAddLineToPoint(path, NULL, CGRectGetWidth(rect), CGRectGetHeight(rect) * 2 / 3);    CGPathCloseSubpath(path);    //绘制渐变    [self drawLinearGradient:gc path:path startColor:[UIColor greenColor].CGColor endColor:[UIColor redColor].CGColor];    //注意释放CGMutablePathRef    CGPathRelease(path);    //从Context中获取图像，并显示在界面上    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();    UIGraphicsEndImageContext();    UIImageView *imgView = [[UIImageView alloc] initWithImage:img];    [self.view addSubview:imgView];}

效果如下：

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