Core Graphices 获取上下文

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Core Graphices 获取上下文的三种方式：

1、自定义view 重写view 的 drawRect:(CGRect)rect方法

- (void)drawRect:(CGRect)rect { /*
UIBezierPath *bezier = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(20, 20, 80, 80) byRoundingCorners:UIRectCornerTopLeft| UIRectCornerTopRight cornerRadii:CGSizeMake(40, 0)]; [[UIColor magentaColor ]setFill];
[[UIColor redColor] setStroke]; //Path operations on the current graphics context当前图形上下文中执行路径操作 [p fill];//只操作了填充把路径在上下文中执行
[p stroke];//只操作了画线 */
/******************上面是ui方式下面是core graphices *****************************/
//当前上下文及画布为当前view
CGContextRef con = UIGraphicsGetCurrentContext(); CGContextAddEllipseInRect(con, CGRectMake(,,,)); CGContextSetFillColorWithColor(con, [UIColor blueColor].CGColor);
CGContextSetStrokeColorWithColor(con, [UIColor redColor].CGColor); // CGContextFillPath(con);//只操作了填充
// CGContextStrokePath(con);//只操作了画线
CGContextDrawPath(con, kCGPathFillStroke);}

draw的调用时机

1.如果在UIView初始化时没有设置rect大小，将直接导致drawRect不被自动调用。

2.该方法在调用sizeThatFits后被调用，所以可以先调用sizeToFit计算出size。然后系统自动调用drawRect:方法。

3.通过设置contentMode属性值为UIViewContentModeRedraw。那么将在每次设置或更改frame的时候自动调用drawRect:。

4.直接调用setNeedsDisplay，或者setNeedsDisplayInRect:触发drawRect:，但是有个前提条件是rect不能为0.

注意：在UIView中绘制图形，获取的上下文就是这个view对应的layer的上下文。在渲染的时候，就是把图形渲染到对应的layer上。

在执行渲染操作的时候，本质上它的内部相当于执行了 [self.layer drawInContext:ctx];

2、drawInContext:(CGContextRef)ctx

#import "GainContext_DrawInContext.h"@implementation GainContext_DrawInContext- (void)drawInContext:(CGContextRef)ctx{// UIGraphicsPushContext(ctx);
// UIBezierPath *bezier = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(10, 20, 80, 80) byRoundingCorners:UIRectCornerTopLeft|UIRectCornerTopRight cornerRadii:CGSizeMake(40, 40)];
// [[UIColor magentaColor ]setFill];
// [[UIColor redColor] setStroke];
// [bezier fill];
// [bezier stroke];
// UIGraphicsPopContext(); /*************************************/ UIBezierPath *bezier = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(, , , ) byRoundingCorners:UIRectCornerTopLeft|UIRectCornerTopRight cornerRadii:CGSizeMake(, )]; CGContextAddPath(ctx, bezier.CGPath);
CGContextSetStrokeColorWithColor(ctx, [UIColor magentaColor].CGColor);
CGContextSetFillColorWithColor(ctx, [UIColor cyanColor].CGColor);// CGContextStrokePath(ctx);
// CGContextFillPath(ctx); CGContextDrawPath(ctx, kCGPathEOFillStroke);}

调用： GainContext_DrawInContext *layer = [GainContext_DrawInContext layer];
layer.frame = CGRectMake(, , , );
[layer setNeedsDisplay];
[self.view.layer addSublayer:layer];

注意：在自定义layer中的-(void)drawInContext:方法不会自己调用，只能自己通过setNeedDisplay方法调用

3、设置CALayer的delegate，然后让delegate实现drawLayer:inContext:方法，当CALayer需要绘图时，会调用delegate的drawLayer:inContext:方法进行绘图。

#import <UIKit/UIKit.h>@interface GainContext_Delegate : NSObject@end#import "GainContext_Delegate.h"@implementation GainContext_Delegate- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx{
// UIGraphicsPushContext(ctx);
// CGPoint center = CGPointMake(40, 40);
// UIBezierPath *path = [UIBezierPath bezierPathWithArcCenter:center radius:40 startAngle:0 endAngle:50*M_PI/180 clockwise:NO];
// [path addArcWithCenter:center radius:20 startAngle:50*M_PI/180 endAngle:0 clockwise:YES];
// [[UIColor magentaColor] setFill];
// [path fill];
// UIGraphicsPopContext(); CGPoint center = CGPointMake(, );
UIBezierPath *path = [UIBezierPath bezierPathWithArcCenter:center radius: startAngle: endAngle:*M_PI/ clockwise:NO];
[path addArcWithCenter:center radius: startAngle:*M_PI/ endAngle: clockwise:YES];
[[UIColor magentaColor] setFill]; CGContextAddPath(ctx, path.CGPath);
CGContextSetStrokeColorWithColor(ctx, [UIColor magentaColor].CGColor);
CGContextSetFillColorWithColor(ctx, [UIColor greenColor].CGColor);
CGContextDrawPath(ctx, kCGPathFillStroke);}/***调用***/

self.delegate = [[GainContext_Delegate alloc] init];

CAShapeLayer *delegateShapLayer = [CAShapeLayer layer];

delegateShapLayer.frame = CGRectMake(10, 20, 100, 100);

delegateShapLayer.delegate = self.delegate;

[delegateShapLayer setNeedsDisplay];

[self.view.layer addSublayer:delegateShapLayer];

4、画图片

UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(, , , )]; [self addSubview:imageView]; UIGraphicsBeginImageContextWithOptions(CGSizeMake(, ), NO, [UIScreen mainScreen].scale);
CGContextRef contex = UIGraphicsGetCurrentContext(); UIBezierPath *bezier = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(, , , ) byRoundingCorners:UIRectCornerTopLeft|UIRectCornerTopRight cornerRadii:CGSizeMake(, )]; CGContextAddPath(contex, bezier.CGPath);
CGContextSetStrokeColorWithColor(contex, [UIColor magentaColor].CGColor);
CGContextSetFillColorWithColor(contex, [UIColor cyanColor].CGColor); CGContextDrawPath(contex, kCGPathFillStroke);
UIFont *font = [UIFont systemFontOfSize:];
NSString *string = @"Core Graphics";
[string drawAtPoint:CGPointMake(, ) withAttributes:@{NSFontAttributeName:font,NSForegroundColorAttributeName:[UIColor redColor]}]; UIImage *im = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
imageView.image = im;

注意：coreGraphices 是不支持arc 的。。。