- (void)viewDidLoad {
    [super viewDidLoad];
    CALayer *layer = [CALayer layer];
    layer.position = CGPointMake(0, 0);
    layer.anchorPoint = CGPointMake(0, 0);
    layer.bounds = self.view.bounds;
    layer.backgroundColor = [UIColor grayColor].CGColor;
    [self.view.layer addSublayer:layer];
    layer.delegate = self;
    [layer setNeedsDisplay];
}

- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx
{

    [[UIBezierPath bezierPathWithRect:CGRectMake(200, 200, 200, 200)]stroke];

//    CGContextAddRect(ctx, CGRectMake(200, 200, 200, 200));
//    CGContextStrokePath(ctx);

}

Mar  2 22:54:42  test[1485] <Error>: CGContextSaveGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
Mar  2 22:54:42  test[1485] <Error>: CGContextSetLineWidth: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
Mar  2 22:54:42  test[1485] <Error>: CGContextSetLineJoin: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
Mar  2 22:54:42  test[1485] <Error>: CGContextSetLineCap: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
Mar  2 22:54:42  test[1485] <Error>: CGContextSetMiterLimit: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
Mar  2 22:54:42  test[1485] <Error>: CGContextSetFlatness: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
Mar  2 22:54:42  test[1485] <Error>: CGContextAddPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
Mar  2 22:54:42  test[1485] <Error>: CGContextDrawPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
Mar  2 22:54:42  test[1485] <Error>: CGContextRestoreGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.