Question

I have a UIView called myView

@interface MyView : UIView {    UIImage *myPic;
        NSMutableArray *myDrawing; }

@end

and i updated this array using touches began, and in the touches moved and touches ended by adding values.

-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
 //   myDrawing = [[NSMutableArray alloc] initWithCapacity:4];
   [myDrawing addObject:[[NSMutableArray alloc] initWithCapacity:4]]; 
    CGPoint curPoint = [[touches anyObject] locationInView:self]; 
    [[myDrawing lastObject] addObject:[NSNumber numberWithFloat:curPoint.x]]; 
    [[myDrawing lastObject] addObject:[NSNumber numberWithFloat:curPoint.y]];
}

-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    CGPoint curPoint = [[touches anyObject] locationInView:self]; 
    [[myDrawing lastObject] addObject:[NSNumber numberWithFloat:curPoint.x]];
    [[myDrawing lastObject] addObject:[NSNumber numberWithFloat:curPoint.y]]; 
    [self setNeedsDisplay];
}

-(void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    CGPoint curPoint = [[touches anyObject] locationInView:self]; 
    [[myDrawing lastObject] addObject:[NSNumber numberWithFloat:curPoint.x]];
    [[myDrawing lastObject] addObject:[NSNumber numberWithFloat:curPoint.y]];
    [self setNeedsDisplay];
}

then i use the draw rect method to update the lines

- (void)drawRect:(CGRect)rect
{
    // Drawing code


    float newHeight;
    float newWidth; 

    if (!myDrawing) {
        myDrawing = [[NSMutableArray alloc] initWithCapacity:0];
    }

    CGContextRef ctx = UIGraphicsGetCurrentContext(); 

    if (myPic != NULL) 
    {
        float ratio = myPic.size.height/460; 
        if (myPic.size.width/320 > ratio) 
        {
            ratio = myPic.size.width/320;
        }  

        newHeight = myPic.size.height/ratio;
        newWidth = myPic.size.width/ratio;
        [myPic drawInRect:CGRectMake(0,0,newWidth,newHeight)];
    }

    if ([myDrawing count] > 0) {
        CGContextSetLineWidth(ctx, 3);
        NSData *colorData = [[NSUserDefaults standardUserDefaults] objectForKey:@"SwatchColor"];
        UIColor *color;
        if (colorData!=nil) {
            // If the data object is valid, unarchive the color we've stored in it.
            color = (UIColor *)[NSKeyedUnarchiver unarchiveObjectWithData:colorData];

        }
        if (color)
        {
            CGContextSetStrokeColorWithColor(ctx, color.CGColor);  
        }
        else
        {
            CGContextSetStrokeColorWithColor(ctx,[UIColor blackColor].CGColor);
        }

        for (int i = 0 ; i < [myDrawing count] ; i++) {
            NSArray *thisArray = [myDrawing objectAtIndex:i];
            if ([thisArray count] > 2) 
            {
                float thisX = [[thisArray objectAtIndex:0] floatValue];
                float thisY = [[thisArray objectAtIndex:1] floatValue];



                CGContextBeginPath(ctx);
                CGContextMoveToPoint(ctx, thisX, thisY);

            for (int j = 2; j < [thisArray count] ; j+=2) 
            { 
                thisX = [[thisArray objectAtIndex:j] floatValue];
                thisY = [[thisArray objectAtIndex:j+1] floatValue];

                CGContextAddLineToPoint(ctx, thisX,thisY);
                //CGContextAddQuadCurveToPoint(ctx, 150, 10, thisX, thisY);
                 // CGContextAddCurveToPoint(ctx , 0, 50, 300, 250, thisX, thisY);
            }
                CGContextStrokePath(ctx);

            }
        }
    }

}

i have a color picker in my code to change the colors and i want to draw lines of different colors each time by selecting colors, but as of now since i am constructing lines and rendering it when i choose initially red and draw a line, and then later select blue and draw a line , now the older line also change to blue instead of red, However i want the red to remain as red, and blue as such can any one help?

Answer 1

You are always drawing over the drawn lines. Clear myDrawing to make it store only the points that need to be processed, keep already processed points at another array if you need undo/optimized-save functionality.