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 3.14159265358979323846
static 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 color
	CGContextSetRGBStrokeColor(ctx, 1, 1, 1, 1.0);
 
	// define line width
	CGContextSetLineWidth(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：