Question

I wrote the following code in a file called PieChartView.m:

#pragma mark DrawingDelegate
@interface DrawingDelegate : NSObject
@end

@implementation DrawingDelegate

- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx {
    //nothing here yet...
}

#pragma mark PieChartView
@implementation PieChartView

@synthesize pie_layer;

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
            float pie_layer_width = 300.f;
            float pie_layer_height = 160.f;
            float pie_layer_PosX = 7.f;
            float pie_layer_PosY = 20.f;

            DrawingDelegate* layerDelegate = [[DrawingDelegate alloc] init];

            pie_layer = [[CALayer alloc] init];

            //when commenting the following assignment the app no longer crashes
            pie_layer.delegate = layerDelegate;
            pie_layer.bounds = CGRectMake( 0.f, 0.f, pie_layer_width, pie_layer_height );
            pie_layer.backgroundColor = [[UIColor whiteColor] CGColor];
            pie_layer.position = CGPointMake( pie_layer_width/2+pie_layer_PosX, pie_layer_height/2+pie_layer_PosY );
            pie_layer.cornerRadius = 10.f;
            CGFloat components[4] = { 0.0, 0.0, 0.0, 1.0 };

            CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
            CGColorRef black = CGColorCreate( colorspace, components );
            pie_layer.borderColor = black;
            pie_layer.borderWidth = 1.f;
            pie_layer.shadowRadius = 5.f;
            pie_layer.shadowColor = black;

            CGColorRelease( black );
            CGColorSpaceRelease(colorspace);

            pie_layer.shadowOffset = CGSizeMake( 0.f, 5.f ),
            pie_layer.shadowOpacity = 0.75f;
            [self.layer insertSublayer:pie_layer above:self.layer];
            [pie_layer setNeedsDisplay];
        }
        return self;
}

Strangly the app crashes as long as I execute the line “pie_layer.delegate = layerDelegate;”. The crash looks like the given screenshot.

Why does this happen? What is wrong in my code?

Here is another more detailed stacktrace:

Answer 1

If this is ARC and the delegate is weak then the drawing delegate will be released as nothing takes ownership of it.

Delegates by convention are weak but something needs to keep a strong reference to the DrawingDelegate object you create.