译：用iPhone SDK来画饼图(Pie Charts)报表

以下类文件可帮我们用UIKit和QuartzCore框架来绘制向量图形。类似这个饼图（Pie Charts）。

// GraphView.h

#import <UIKit/UIKit.h>

@interface GraphView:UIView {
}
@end

// GraphView.m

#import "GraphView.h"

#define PI 3.14159265358979323846
static inline float radians(double degrees) { return degrees * PI / 180; }

@implementation GraphView
- (void)drawRect : (CGRect)rect {
   CGRect  parentViewBounds = self.bounds;
   CGFloat  x = CGRectGetWidth(parentViewBounds) / 2;
   CGFloat  y = CGRectGetHeight(parentViewBounds) * 0.55;

   // 获得图形上下文，然后清除之
   CGContextRef ctx = UIGraphicsGetCurrentContext();
   CGContextClearRect(ctx, rect);

   // 定义笔触颜色
   CGContextSetRGBStrokeColor(ctx, 1, 1, 1, 1.0);
   // 定义线宽
   CGContextSetLineWidth(ctx, 4.0);

   // 绘制饼图的一些必要值
   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);
}

代码中类似snapshot_start等变量值要在程序中设定好！！。

调用示例：

GraphView *graph = [[GraphView alloc] initWithFrame:CGRectMake(0.0, 20.0, 320.0, 460.0)];
[window addSubview:graph];