ios - 为 calayer 绘图添加委托(delegate)会使应用程序崩溃

Question

我在名为 PieChartView.m 的文件中编写了以下代码:

#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;
}

奇怪的是，只要我执行“pie_layer.delegate = layerDelegate;”这一行，应用程序就会崩溃。崩溃看起来像给定的屏幕截图。

为什么会这样？我的代码有什么问题？

这是另一个更详细的堆栈跟踪:

Answer 1

如果这是 ARC 并且委托(delegate)是 weak 那么绘图委托(delegate)将被释放，因为没有任何人拥有它。

按照约定，委托(delegate)是弱的，但需要保持对您创建的 DrawingDelegate 对象的 strong 引用。