Clear a drawing in drawRect - iphone

Question

How can I clear a drawing in a subview? What should I put in my (void)clearLine below?
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
// Setup subview to draw a line
CGRect subviewRect = CGRectMake(0, 0, 250, 300);
Draw* _draw = [[Draw alloc] initWithFrame:subviewRect];
_draw.exclusiveTouch = NO;
_draw.backgroundColor = [UIColor clearColor];
[self addSubview:_draw];
}
return self;
}
- (void) clearLine
{
// how can I clear the drawing in Draw
}
And below is the Draw.m file, that will draw a straight line by getting the first touch as the starting point and the second touch as the ending point.
#implementation Draw
- (void)drawRect:(CGRect)rect {
CGPoint fromPoint;
CGPoint toPoint;
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 2.0);
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGFloat components[] = {0.0, 0.0, 1.0, 1.0};
CGColorRef color = CGColorCreate(colorspace, components);
CGContextSetStrokeColorWithColor(context, color);
CGContextSetLineCap(context, kCGLineCapRound);
CGContextMoveToPoint(context, fromPoint.x, fromPoint.y);
CGContextAddLineToPoint(context, toPoint.x, toPoint.y);
CGContextStrokePath(context);
CGColorSpaceRelease(colorspace);
CGColorRelease(color);
}
// Touch event
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch* touchPoint = [touches anyObject];
fromPoint = [touchPoint locationInView:self];
toPoint = [touchPoint locationInView:self];
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch* touch = [touches anyObject];
toPoint = [touch locationInView:self];
[self setNeedsDisplay];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch* touch = [touches anyObject];
toPoint = [touch locationInView:self];
[self setNeedsDisplay];
}

Answer 1

In clear line you should remove Draw view and set it nil
Draw* _draw;
- (void) clearLine
{
[_draw removeFromSuperview];
_draw=nil;
}
and to again enable drawing use
-(void) initDrawView
{
CGRect subviewRect = CGRectMake(0, 0, 250, 300);
if(_draw!=nil)
{
[_draw removeFromSuperview];
_draw=nil;
}
_draw = [[Draw alloc] initWithFrame:subviewRect];
_draw.exclusiveTouch = NO;
_draw.backgroundColor = [UIColor clearColor];
[self addSubview:_draw];
}

Answer 2

Draw the background color on your view,
Like if you have white background then [UIColor whiteColor];
if you have black background then [UIColor blackColor];

Answer 3

Make a Bool variable in Draw class
And when you want to clear all like this
- (void) clearLine
{
// Here you can clearn lines
[_draw CleanAllLines]
}
And In Draw class make the method
-(void)CleanAllLines{
isNeedToClear = YES;
[self setNeedsLayout];
}
- (void)drawRect:(CGRect)rect {
if(isNeedToClear){
isNeedToClear = NO;
return;
}
CGPoint fromPoint;
CGPoint toPoint;
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 2.0);
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGFloat components[] = {0.0, 0.0, 1.0, 1.0};
CGColorRef color = CGColorCreate(colorspace, components);
CGContextSetStrokeColorWithColor(context, color);
CGContextSetLineCap(context, kCGLineCapRound);
CGContextMoveToPoint(context, fromPoint.x, fromPoint.y);
CGContextAddLineToPoint(context, toPoint.x, toPoint.y);
CGContextStrokePath(context);
CGColorSpaceRelease(colorspace);
CGColorRelease(color);
}