how to delete content of UIView (Core Graphics)? - ios

Question

I'm trying to clear the content of what I have drawn when i press a button. But, I cant seem to do it figure out how to do it. I have google around abit and it seems like you need to do this inside of draw rect. This is the full code that I am using:
#import "PaintView.h"
#implementation PaintView
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
hue = 0.0;
[self initContext:frame.size];
}
return self;
}
- (BOOL) initContext:(CGSize)size {
int bitmapByteCount;
int bitmapBytesPerRow;
// Declare the number of bytes per row. Each pixel in the bitmap in this
// example is represented by 4 bytes; 8 bits each of red, green, blue, and
// alpha.
bitmapBytesPerRow = (size.width * 4);
bitmapByteCount = (bitmapBytesPerRow * size.height);
// Allocate memory for image data. This is the destination in memory
// where any drawing to the bitmap context will be rendered.
self.cacheBitmap = malloc( bitmapByteCount );
if (self.cacheBitmap == NULL){
return NO;
}
self.cacheContext = CGBitmapContextCreate (self.cacheBitmap, size.width, size.height, 8, bitmapBytesPerRow, CGColorSpaceCreateDeviceRGB(), kCGImageAlphaNoneSkipFirst);
return YES;
}
- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [touches anyObject];
[self drawToCache:touch];
}
- (void) drawToCache:(UITouch*)touch {
hue += 0.005;
if(hue > 1.0) hue = 0.0;
UIColor *color = [UIColor colorWithHue:hue saturation:0.7 brightness:1.0 alpha:1.0];
CGContextSetStrokeColorWithColor(self.cacheContext, [color CGColor]);
CGContextSetLineCap(self.cacheContext, kCGLineCapRound);
CGContextSetLineWidth(self.cacheContext, 6);
CGPoint lastPoint = [touch previousLocationInView:self];
CGPoint newPoint = [touch locationInView:self];
CGContextMoveToPoint(self.cacheContext, lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(self.cacheContext, newPoint.x, newPoint.y);
CGContextStrokePath(self.cacheContext);
CGRect dirtyPoint1 = CGRectMake(lastPoint.x-10, lastPoint.y-10, 20, 20);
CGRect dirtyPoint2 = CGRectMake(newPoint.x-10, newPoint.y-10, 20, 20);
[self setNeedsDisplayInRect:CGRectUnion(dirtyPoint1, dirtyPoint2)];
}
-(void)clear{
// this doesn't work.
CGContextClearRect(self.context, self.bounds);
}
- (void) drawRect:(CGRect)rect {
self.context = UIGraphicsGetCurrentContext();
CGImageRef cacheImage = CGBitmapContextCreateImage(self.cacheContext);
CGContextDrawImage(self.context, self.bounds, cacheImage);
CGImageRelease(cacheImage);
CGContextRetain(self.context);
}
#end

Answer 1

the button should call the view's setNeedsDisplay method which forces drawrect to be called or essentially forces a repaint.