iphone上如何绘制饼图（使用CGContextAddArc）（原创）

CGContextAddArc是一个比较强大的函数，建议仔细看一下iphone的开发文档。

CGContextAddArc(CGContextRef c, CGFloat x, CGFloat y, CGFloat radius, CGFloat startAngle, CGFloat endAngle, intclockwise)

 

• CGContextRef: 图形上下文
• x,y: 开始画的坐标
• radius: 半径
• startAngle, endAngle: 开始的弧度,结束的弧度
• clockwise: 画的方向(顺时针,逆时针)

GraphView.h文件：

 

#import <UIKit/UIKit.h>#import <Foundation/Foundation.h> @interface GraphView : UIView { } @end

 

 

 

GraphView.m文件：
#import "GraphView.h"#define PI 3.14159265358979323846static inline float radians(double degrees) { return degrees * PI / 180; } @interface GraphView(private)//如果有什么私有方法，在这里声明@end@implementation GraphView- (id)initWithFrame:(CGRect)frame {    if ((self = [super initWithFrame:frame])) {        // Initialization code    }    return self;}- (void)drawRect:(CGRect)rect { CGRect parentViewBounds = self.bounds;CGFloat x = CGRectGetWidth(parentViewBounds)/2;CGFloat y = CGRectGetHeight(parentViewBounds)*0.55;     // Get the graphics context and clear it    CGContextRef ctx = UIGraphicsGetCurrentContext();    CGContextClearRect(ctx, rect); // define stroke colorCGContextSetRGBStrokeColor(ctx, 1, 1, 1, 1.0); // define line widthCGContextSetLineWidth(ctx, 4.0);         // need some values to draw pie charts         double snapshotCapacity =20;        double rawCapacity = 100;        double systemCapacity = 1; int offset = 5;double pie1_start = 315.0;double pie1_finish = snapshotCapacity *360.0/rawCapacity; double system_finish = systemCapacity*360.0/rawCapacity;     CGContextSetFillColor(ctx, CGColorGetComponents( [[UIColor greenColor] CGColor]));    CGContextMoveToPoint(ctx, x+2*offset, y);         CGContextAddArc(ctx, x+2*offset, y, 100,  radians(snapshot_start), radians(snapshot_start+snapshot_finish), 0);     CGContextClosePath(ctx);     CGContextFillPath(ctx);  // system capacity CGContextSetFillColor(ctx, CGColorGetComponents( [[UIColor colorWithRed:15 green:165/255 blue:0 alpha:1 ] CGColor]));CGContextMoveToPoint(ctx, x+offset,y);         CGContextAddArc(ctx, x+offset, y, 100,  radians(snapshot_start+snapshot_finish+offset), radians(snapshot_start+snapshot_finish+system_finish), 0);     CGContextClosePath(ctx);     CGContextFillPath(ctx);  /* data capacity */CGContextSetFillColor(ctx, CGColorGetComponents( [[UIColor colorWithRed:99/255 green:184/255 blue:255/255 alpha:1 ] CGColor]));CGContextMoveToPoint(ctx, x, y);         CGContextAddArc(ctx, x, y, 100,  radians(snapshot_start+snapshot_finish+system_finish+offset), radians(snapshot_start), 0);     CGContextClosePath(ctx);     CGContextFillPath(ctx);}- (void)dealloc {    [super dealloc];}@end

调用代码如下：
GraphView* viewTest = [[GraphView alloc] initWithFrame:CGRectMake(x,y,width,height)];
[self.view addsubView:viewTest];
[viewTest release];
效果图如下：