cocoa - 子类化 CALayer 时未调用 drawLayer

Question

我有一个简单的 CALayer 子类 (BoxLayer)，具有此 drawLayer 方法:

- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx {
    NSLog(@"drawLayer");
    NSGraphicsContext *nsGraphicsContext;
    nsGraphicsContext = [NSGraphicsContext graphicsContextWithGraphicsPort:ctx
                                                                   flipped:NO];
    [NSGraphicsContext saveGraphicsState];
    [NSGraphicsContext setCurrentContext:nsGraphicsContext];

    // ...Draw content using NS APIs...
    NSPoint origin = { 21,21 };

    NSRect rect;
    rect.origin = origin;
    rect.size.width  = 128;
    rect.size.height = 128;

    NSBezierPath * path;
    path = [NSBezierPath bezierPathWithRect:rect];

    [path setLineWidth:4];

    [[NSColor whiteColor] set];
    [path fill];

    [[NSColor grayColor] set]; 
    [path stroke];

    [NSGraphicsContext restoreGraphicsState];
}

然后我在我的 NSView 子类中有这个 awakeFromNib :

- (void)awakeFromNib {
    CALayer* rootLayer = [CALayer layer];
    [self setLayer:rootLayer];
    [self setWantsLayer:YES];

    box1 = [CALayer layer];
    box1.bounds = CGRectMake(0, 0, 70, 30);
    box1.position = CGPointMake(80, 80);
    box1.cornerRadius = 10;
    box1.borderColor = CGColorCreateGenericRGB(255, 0, 0, 1);
    box1.borderWidth = 1.5;
    [rootLayer addSublayer:box1];

    box2 = [BoxLayer layer];
    [box2 setDelegate:box2];
    [box2 setNeedsDisplay];
    [rootLayer addSublayer:box2];
}

虽然我的drawLayer从未被调用过，但为什么不呢？

谢谢

Answer 1

可能是因为您的图层的框架似乎等于CGRectZero，因此操作系统可能认为它是不可见的，因此不需要绘制它。

顺便说一句，为什么要采用复杂的方式将图层的委托(delegate)设置为自身并实现 drawLayer:inContext: 而不是直接使用 drawInContext: ？