How to remove UIBezierPath from UIView on button click?

Question

I am using following code to create a digital signature on UIView :

#import "Signature.h"

@implementation Signature {
    UIBezierPath *path;
    UIImage *incrementalImage;
    CGPoint pts[5]; // we now need to keep track of the four points of a Bezier segment and the first control point of the next segment
    uint ctr;
}

- (id)initWithCoder:(NSCoder *)aDecoder
{
    if (self = [super initWithCoder:aDecoder])
    {
        [self setMultipleTouchEnabled:NO];
        [self setBackgroundColor:[UIColor greenColor]];
        path = [UIBezierPath bezierPath];
        [path setLineWidth:2.0];
    }
    return self;

}

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        [self setMultipleTouchEnabled:NO];
        path = [UIBezierPath bezierPath];
        [path setLineWidth:2.0];
    }
    return self;
}

- (void)drawRect:(CGRect)rect
{
    [incrementalImage drawInRect:rect];
    [path stroke];
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    ctr = 0;
    UITouch *touch = [touches anyObject];
    pts[0] = [touch locationInView:self];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint p = [touch locationInView:self];
    ctr++;
    pts[ctr] = p;
    if (ctr == 4)
    {
        pts[3] = CGPointMake((pts[2].x + pts[4].x)/2.0, (pts[2].y + pts[4].y)/2.0); // move the endpoint to the middle of the line joining the second control point of the first Bezier segment and the first control point of the second Bezier segment

        [path moveToPoint:pts[0]];
        [path addCurveToPoint:pts[3] controlPoint1:pts[1] controlPoint2:pts[2]]; // add a cubic Bezier from pt[0] to pt[3], with control points pt[1] and pt[2]

        [self setNeedsDisplay];
        // replace points and get ready to handle the next segment
        pts[0] = pts[3];
        pts[1] = pts[4];
        ctr = 1;
    }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    [self drawBitmap];
    [self setNeedsDisplay];
    [path removeAllPoints];
    ctr = 0;
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSLog(@"hello");
    [self touchesEnded:touches withEvent:event];
}

- (void)drawBitmap
{
    UIGraphicsBeginImageContextWithOptions(self.bounds.size, YES, 0.0);

    if (!incrementalImage) // first time; paint background white
    {
        UIBezierPath *rectpath = [UIBezierPath bezierPathWithRect:self.bounds];
        [[UIColor greenColor] setFill];
        [rectpath fill];
    }
    [incrementalImage drawAtPoint:CGPointZero];
    [[UIColor blackColor] setStroke];
    [path stroke];
    incrementalImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
}

- (void)erase {
    NSLog(@"Erase Testing...");
     // self->path   = nil;  //Set current path nil
     //path   = [UIBezierPath bezierPath];
    // [self setNeedsDisplay];
}

I am calling erase method on button click but it's not working for me. I don't know why it's not responding.

Answer 1

sandeep tomar,

Trying to remove the already drawn UIBezierPath from UIView can be bit cumbersome though absolutely possible.

But I believe the simplest solution would be not trying to remove it and just make it invisible :)

Assume you are drawing on a white canvas then when you want to remove the existing UIBezierPath just stroke it again but this time with white color :)

You can never see a white line drawn on white canvas can you ??? :)

[[UIColor whiteColor] setStroke];
 [path stroke];

EDIT

If you want to clear everything in one shot then this might help you :)

- (void)erase {
  incrementalImage = nil;
  path   = nil;  //Set current path nil
  path   = [UIBezierPath bezierPath];
  [self setNeedsDisplay]; 
}

Try this and lemme know if you still have issues. Hope it helps :)

Answer 2

try this

- (void)erase {

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextClearRect(context, self.bounds);
}