iOS drawRect not being called

[man2manno]

Hey guys, I am new to Quartz 2D and have been trying to figure this out. I have a window based app and a UIView as a sub view of it. All I am simply trying to do is draw and line with the following code:

- (void)drawRectCGRect)rect {
NSLog(@"I am trying to draw");
CGContextRef context = UIGraphicsGetCurrentContext();

CGContextSetLineWidth(context, 6.0);
CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor);
CGContextMoveToPoint(context, 100.0f, 100.0f);
CGContextAddLineToPoint(context, 200.0f, 200.0f);
CGContextStrokePath(context);
}

When I run that nothing happens. I have tried to use
[self setNeedsDisplay:YES] and still nothing. Maybe I dont know where to put the setNeedsDisplay? or maybe I am missing a framework? or maybe I am not importing something or making a Quartz 2D delegate? Any help would be greatly appericated!!

Thanks.

 

[North Bronson]

Try this, instead of calling:

[1] CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor);

Try:

[2] CGContextSetRGBStrokeColor(currentContext, 1, 0, 0, 1);

This function sets the Stroke Color *Space* to RGB, which you might need before you see anything.

You might also replace [1] with:

[3] [[UIColor redColor] set];

which should set the stroke color to red *and* set the color space to RGB. I would rather do this with [2], but it's up to you.

 

[firewood]

Is your view visible? Are you putting the setNeedsDisplay somewhere where it will actually get called?

(debugger breakpoints are your friends)

 

[man2manno]

Yes my view is visible, and where should I be putting my setNeedsDisplay?
I have been putting it in a method when a button is pressed but I get a warning and the program crashes.

 

[robbieduncan]

Yes my view is visible, and where should I be putting my setNeedsDisplay?
I have been putting it in a method when a button is pressed but I get a warning and the program crashes.

Can you post the code you have. There is no way this should cause a crash...

It should look something like

[viewPointer setNeedsDisplay];

 

[man2manno]

#import "graph.h"
#import <UIKit/UIKit.h>

@implementation graph

- (id)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        // Initialization code
		NSLog(@"code started");
    }
    return self;
}



- (IBAction)start:(id)sender {
	NSLog(@"starting");
	

}


- (void)drawRect:(CGRect)rect {
	NSLog(@"I am trying to draw");

	CGContextRef context = UIGraphicsGetCurrentContext();
	CGContextSetRGBStrokeColor(context, 1, 0, 0, 1);
	CGContextSetLineWidth(context, 6.0);
	
	CGContextMoveToPoint(context, 100.0f, 100.0f);
	CGContextAddLineToPoint(context, 200.0f, 200.0f);
	CGContextStrokePath(context);
}


- (void)dealloc {
    [super dealloc];
}

This is the code where I am just trying to draw the line, Where would I put the setNeedsDisplay?

Thanks alot

 

[robbieduncan]

This is the code where I am just trying to draw the line, Where would I put the setNeedsDisplay?

Thanks alot

Where ever you are causing the view to require updating. Normally not in the view code, rather in the controller code somewhere.

 

[man2manno]

It Worked but...

Thanks a lot, you were right that works now the drawRect method is being called, but I seem to have run into another problem. My drawRect method is being called, but none of the code actually runs because the debugger says I am getting an error like this:

2009-05-30 22:19:16.133 Quartz2D[54243:20b] I am trying to draw
Sat May 30 22:19:16 Macintosh-2.local Quartz2D[54243] <Error>: CGContextSetLineWidth: invalid context
Sat May 30 22:19:16 Macintosh-2.local Quartz2D[54243] <Error>: CGContextSetStrokeColorWithColor: invalid context
Sat May 30 22:19:16 Macintosh-2.local Quartz2D[54243] <Error>: CGContextMoveToPoint: invalid context
Sat May 30 22:19:16 Macintosh-2.local Quartz2D[54243] <Error>: CGContextAddLineToPoint: invalid context
Sat May 30 22:19:16 Macintosh-2.local Quartz2D[54243] <Error>: CGContextDrawPath: invalid context

That is what the debugger is saying, the program compiles and runs and drawRect is being called because of the NSLog I have. What does the rest mean?