CGContextFillRect not drawing a rectangle? - iphone

Question

I have this code:
CGColorRef darkColor = [[UIColor colorWithRed:21.0/255.0 green:92.0/255.0 blue:136.0/255.0 alpha:1.0] CGColor];
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, darkColor);
CGContextFillRect(context, CGRectMake(18, 62, 66, 66));
And I just put it in the viewdidload method of my view, but my view doesn't look any different than before. I've tried making it really big and bright red, but it's just not drawing. Is there some other initialization code that I need?
EDIT: After working with the answers given to me, I have this now in my veiwdidload:
[self.view addSubview:[[[imageBackground alloc] init] autorelease]];
and in imageBackground.m:
#implementation imageBackground
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
// Initialization code
self.opaque = YES;
self.backgroundColor = [UIColor clearColor];
}
return self;
}
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
CGColorRef darkColor = [[UIColor colorWithRed:21.0/255.0 green:92.0/255.0 blue:136.0/255.0 alpha:1.0] CGColor];
darkColor = [[UIColor colorWithRed:255.0 green:0.0 blue:0.0 alpha:1.0] CGColor];
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, darkColor);
CGContextFillRect(context, CGRectMake(18, 62, 66, 66));
}
#end
Imagebackground.h subclasses UIView:
#import <UIKit/UIKit.h>
#interface imageBackground : UIView
#end
I still get no results out of it though.
EDIT2: Well, I solved it myself, but then realized progrmr had already told me how to solve it. I had to use [self.view addSubview:[[[imageBackground alloc] initWithFrame:CGRectMake(0, 0, 320, 480)] autorelease]]; instead of just plain alloc init.
Thanks glorifiedhacker for lots of help as well!

Answer 1

You need to subclass UIView (or one of its subclasses) and override the drawRect method:
- (void)drawRect:(CGRect)rect {
CGColorRef darkColor = [[UIColor colorWithRed:21.0/255.0 green:92.0/255.0 blue:136.0/255.0 alpha:1.0] CGColor];
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, darkColor);
CGContextFillRect(context, CGRectMake(18, 62, 66, 66));
}
in order to get a valid graphics context into which you can draw. From Apple's documentation on UIView:
View drawing occurs on an as-needed basis. When a view is first shown,
or when all or part of it becomes visible due to layout changes, the
system asks the view to draw its contents. For views that contain
custom content using UIKit or Core Graphics, the system calls the
view’s drawRect: method. Your implementation of this method is
responsible for drawing the view’s content into the current graphics
context, which is set up by the system automatically prior to calling
this method. This creates a static visual representation of your
view’s content that can then be displayed on the screen.

Answer 2

The most simply way, without subclassing, is a procedure for whole code.
void DrawRectFrame(CGContext c, CGRect rc)
{
CGContextMoveToPoint(c, rc.origin.x, rc.origin.y);
CGContextAddLineToPoint(c, rc.origin.x+rc.size.width, rc.origin.y);
CGContextMoveToPoint(c, rc.origin.x+rc.size.width, rc.origin.y);
CGContextAddLineToPoint(c, rc.origin.x+rc.size.width, rc.origin.y+rc.size.height);
CGContextMoveToPoint(c, rc.origin.x+rc.size.width, rc.origin.y+rc.size.height);
CGContextAddLineToPoint(c, rc.origin.x, rc.origin.y+rc.size.height);
CGContextMoveToPoint(c, rc.origin.x, rc.origin.y+rc.size.height);
CGContextAddLineToPoint(c, rc.origin.x, rc.origin.y);
}