Howto: Drawing Pie Charts using iPhone SDK

Drawing Pie Charts using iPhone SDK

Here’s one way to draw a PIE chart using the latest iPhone SDK. There are a ton of tutorials out there that let you get started with the iPhone app development itself and I am by no means any authoritative source on learning how to develop one. Having said that, here’s a class file that will help you use the UIKit and Quartz to draw vector graphics.
An example of the pie charts the code base generates is below (a screenshot):

iPhone SDK

And now, for the code:

GraphView.h

#
#(nothing to see here)
#

#import <UIKit/UIKit.h>
#import <Foundation/Foundation.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;

    // 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);
}