Core Graphics Line drawing and deleting on touch

问题

I am writing an iPhone application somewhat like pick up sticks app on appstore. I have already done with drawing multiple lines and displaying it using CoreGraphics. But now I am stuck with how to delete the line when the user taps on it. I have searched on Google a lot but didn't find anything related.

I have seen this post of yours at some other place and this has really helped me out. but the problem is that if i have a stick and then another stick on top of it. when i click on the stick which is below, it should not get deleted and if i tap on the above on, it should get deleted if there is no stick above it. How to achieve this thing.. A lso i need to store the paths i.e. my lines which is UIBeizerpath in a list, array, dictionary whatever, please help me with this thing also. I'm not finding anything for it.

回答1:

I see 2 issues raised: (1) how to detect a touch on a line drawn in a view, and (2) how to redraw the view without the touched line. A combined approach is to define a line object to be a rectangle converted to a string: NSStringFromCGRect(CGRectMake(x, y, width, height). Add one or more line objects to NSSet *setOfLines and add Quartz 2D / Core Graphics drawing code in the drawRect: method of the UIView class that shows the lines.

- (void)drawRect:(CGRect)rect
{
    gc = UIGraphicsGetCurrentContext();
    CGContextSetLineWidth(gc, lineThickness]);
    CGContextSetStrokeColorWithColor(gc, ([UIColor redColor]).CGColor);
    for (NSString *lineString in setOfLines) {
        CGRect line = CGRectFromString(lineString);
        CGContextMoveToPoint(gc, line.origin.x, line.origin.y);
        CGContextAddLineToPoint(gc, (line.origin.x + line.size.width), (line.origin.y + line.size.height));
    }
    CGContextStrokePath(gc);
}

In that same UIView class, add a tap gesture recognizer (note the coexistence with double tapping):

UITapGestureRecognizer *singleTapper = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(lineSingleTapped:)];
singleTapper.numberOfTapsRequired = 1;
[singleTapper requireGestureRecognizerToFail:doubleTapper];
[cell addGestureRecognizer:singleTapper];    


- (IBAction)lineSingleTapped:(UITapGestureRecognizer *)sender
{
    CGPoint tapPoint = [sender locationInView:self];
    // Get the line that was tapped
    for (NSString *lineString in setOfLines) {
        CGRect line = CGRectFromString(lineString);
        // Make a rectangle that defines the tappable area of a line: disclaimer, might be very thin or short!
        // A minimum size of 44.0 x 44.0 is advisable
        CGRect lineTapArea = CGRectMake(line.origin.x, line.origin.y, (line.origin.x + line.size.width), line.origin.y + line.size.height);
        if (CGRectContainsPoint(lineTapArea, tapPoint)) {
            [setOfLines removeObject:lineObject];
            [self setNeedsDisplayInRect:lineTapArea];
            break;
        }
    }
}

The design pattern here is:

Implement the drawing view class both for user interaction and to do drawing
Define data objects that represent the visual elements to be drawn
Alter the data objects based on user interaction and then force part or all of the view to be redrawn

回答2:

If you are using Core Graphics in a UIView, you won't have to delete anything. You will instead have be able to completely redraw the view, but perhaps with one less stick.

来源：https://stackoverflow.com/questions/8702898/core-graphics-line-drawing-and-deleting-on-touch

标签

iphone

ios

cocoa-touch

uikit

core-graphics