How to create a CGGradient for my UIView subclass? - objective-c

Question

Does anyone know how to create a CGGradient that will fill my view,
my current code is this and it fill the UIView with a red rectangle I want to have a gradient (from black to grey for instance) instead of the rect :
- (void)drawRect:(CGRect)rect {
CGContextRef context=UIGraphicsGetCurrentContext();
CGRect r;
r.origin.x=0.;
r.origin.y=0.;
r.size.width=rect.size.width;
r.size.height=rect.size.height;
CGContextSetRGBFillColor(context, 1., 0., 0., 1.);
CGContextFillRect (context,r);
}

Answer 1

In my answer to this question, I provide code for drawing a gloss gradient within a UIView. The colors and drawing positions can be modified from that to form whatever linear gradient you need.

Answer 2

this is a subclass where you can chose the colors
.h file
#import <UIKit/UIKit.h>
#interface GradientView : UIView {
CGGradientRef gradient;
}
#property(nonatomic, assign) CGGradientRef gradient;
- (id)initWithGradient:(CGGradientRef)gradient;
- (id)initWithColor:(UIColor*)top bottom:(UIColor*)bot;
- (void)setGradientWithColor:(UIColor*)top bottom:(UIColor*)bot;
- (void)getRGBA:(CGFloat*)buffer;
#end
.m file
#import "GradientView.h"
#implementation GradientView
#synthesize gradient;
- (id)initWithGradient:(CGGradientRef)grad {
self = [super init];
if(self){
[self setGradient:grad];
}
return self;
}
- (id)initWithColor:(UIColor*)top bottom:(UIColor*)bot {
self = [super init];
if(self){
[self setGradientWithColor:top bottom:bot];
}
return self;
}
- (void)setGradient:(CGGradientRef)g {
if(gradient != NULL && g != gradient){
CGGradientRelease(gradient);
}
if(g != gradient){
CGGradientRetain(g);
}
gradient = g;
[self setNeedsDisplay];
}
- (void)setGradientWithColor:(UIColor*)top bottom:(UIColor*)bot {
CGColorSpaceRef rgb = CGColorSpaceCreateDeviceRGB();
CGFloat clr[8];
[top getRGBA:clr];
[bot getRGBA:clr+4] ;
CGGradientRef grad = CGGradientCreateWithColorComponents(rgb, clr, NULL, sizeof(clr)/(sizeof(clr[0])*4));
[self setGradient:grad];
CGColorSpaceRelease(rgb);
CGGradientRelease(grad);
}
- (void)getRGBA:(CGFloat*)buffer {
CGColorRef clr = [self CGColor];
NSInteger n = CGColorGetNumberOfComponents(clr);
const CGFloat *colors = CGColorGetComponents(clr);
// TODO: add other ColorSpaces support
switch (n) {
case 2:
for(int i = 0; i<3; ++i){
buffer[i] = colors[0];
}
buffer[3] = CGColorGetAlpha(clr);
break;
case 3:
for(int i = 0; i<3; ++i){
buffer[i] = colors[i];
}
buffer[3] = 1.0;
break;
case 4:
for(int i = 0; i<4; ++i){
buffer[i] = colors[i];
}
break;
default:
break;
}
}
- (void)drawRect:(CGRect)rect {
CGContextRef c = UIGraphicsGetCurrentContext();
CGContextDrawLinearGradient(c, gradient, CGPointMake(0, 0), CGPointMake(0, rect.size.height), 0);
}
- (void)dealloc {
CGGradientRelease(gradient);
[super dealloc];
}
#end

Answer 3

Use CGGradientCreateWithColorComponents or CGGradientCreateWithColors to create the gradient. (The latter takes CGColor objects.) Then, use CGContextDrawLinearGradient or CGContextDrawRadialGradient to draw it.
A linear gradient will extend infinitely in at least the two directions perpendicular to the line of the gradient. A radial gradient extends infinitely in every direction. To prevent the gradient from spilling outside your view, you'll probably need to add the view's bounds to the clipping path using CGContextClipToRect.