我无法弄清楚为什么我正在创建的CALayer没有调用他们的drawLayer方法.我为它们创建了一个drawLayer委托对象,但它永远不会被调用.从UIView子类：
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
UIView *bg = [[UIView alloc] initWithFrame:self.bounds];
// I have a property called 'bg' to reference the child UIView
self.bg = bg;
[self addSubview:self.bg];
// an NSObject subclass I use as a CALayer delegate
MyLayerDelegate *drawer = [MyLayerDelegate new];
self.drawer = drawer;
CAGradientLayer *layer = [CAGradientLayer layer];;
layer.delegate = self.drawer;
layer.name = @"bg";
[self.bg.layer addSublayer:layer];
[layer setNeedsDisplay];
[layer display];
}
return self;
}
在self.drawer我有：
- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)context
{
NSLog(@"layer called drawLayer");
// Some drawing goes here
}
我尝试了很多不同的东西.我已经尝试在self.bg.layer上设置setNeedsDisplay,我在self.bg上尝试了setNeedsDisplay,我在addSublayer之前和之后尝试了[layer setNeedsDisplay],我在addSublayer之前和之后尝试了[图层显示].我曾尝试使用和不使用[图层显示]和[图层displayIfNeeded].
为什么图层拒绝绘制？
解决方法
图层框架必须为非零.这解决了这个问题：
layer.frame = self.bg.bounds; [layer setNeedsDisplay]; [self.bg.layer addSublayer:layer];
