@interface CTLayer : CALayer@end@implementation CTLayer-(void)drawInContext:(CGContextRef)ctx{
　　 //畫一個圓    CGContextSetRGBFillColor(ctx, 0, 0, 1, 1);    CGContextAddEllipseInRect(ctx, CGRectMake(100, 100, 100, 100));    CGContextFillPath(ctx);}@end

    CTLayer *layer = [CTLayer layer];    layer.bounds = CGRectMake(0, 0, 300, 300);    layer.anchorPoint = CGPointMake(0,0);    [layer setNeedsDisplay];//顯示圖層    [self.view.layer addSublayer:layer];

    CTLayer *layer = [CTLayer layer];    layer.bounds = CGRectMake(0, 0, 300, 300);    layer.anchorPoint = CGPointMake(0,0);    layer.delegate = self; //指定代理，該代理可為任意類型    [layer setNeedsDisplay];//顯示layer    [self.view.layer addSublayer:layer];

#PRagma mark 代理方法-(void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx{    CGContextSetRGBFillColor(ctx, 0, 0, 1, 1);    CGContextAddEllipseInRect(ctx, CGRectMake(100, 100, 100, 100));    CGContextFillPath(ctx);}