Question

so I have a little experience with objective-c, but not a ton. I’m trying to render UIBezierPath via TouchEvents (in other words draw a line with your finger). In addition, I would like to save all the bezierPaths into a NSMutableArray (paths) so that I can move or modify them later. This is the very simplest of applications. My header looks like this:

@interface ViewController : UIViewController{
    UIBezierPath* path;
    NSMutableArray* paths;

    int curThickness;

}

@property (strong, nonatomic) IBOutlet UIView *scene;
@end

Scene is the view which takes up the entire screen and is where I am trying to draw my paths.

Relavent implementation looks like this:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *touch = [touches anyObject];
    NSLog(@"Starting Path");

    path = [UIBezierPath bezierPath];
    path.lineWidth = 15.0f;
    path.lineCapStyle = kCGLineCapRound;
    path.lineJoinStyle = kCGLineJoinRound;
    path.flatness = 2.0;
    path.miterLimit = 4.0;

    [path moveToPoint:[touch locationInView:scene]];

}


- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *touch = [touches anyObject];
    [path addLineToPoint:[touch locationInView:scene]];
    [scene setNeedsDisplay];
}


- (void)drawRect:(CGRect)rect {
    NSLog(@"I'm supposed to be drawing something...");
    [[UIColor redColor] set];
    [path stroke];
}



- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{
    NSLog(@"No more touchy feelies");
    UITouch *touch = [touches anyObject];
    [path addLineToPoint:[touch locationInView:scene]];
    [paths addObject:path];
    [scene setNeedsDisplay];

    NSLog(@"number of paths: %i.", paths.count);

}

When I run it on the emulator, all the events are registered, DrawRect is never called, nothing is drawn on the screen (even if I add a [path trace] at the end of touchesEnded), path is nonEmpty, and paths.count remains zero no matter how many paths I trace.

What am I missing? As always your help is always greatly appreciated.

Answer 1

Couple things that should help you:

1. UIViewController does not implement - (void)drawRect .. you need to be doing this code in a UIView subclass instead!

2. If your paths collection is always zero count, a common mistake causing this is when paths itself is nil. (Obj-c doesn’t care if you try to send messages to a nil object, it will just return a default value instead of crashing.) Double-check that you instantiated an NSMutableArray object and pointed paths to it.