GraphView.h文件：

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

#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 itCGContextRef 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 chartsdouble 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