ios - CALayer 的图像不显示

Question

我正在尝试使用 CALayer 来显示图像，但图像没有显示出来。我已验证“图像”不为零，image.size 正确，并且 layer.contents 是有效的 CABackingStore。

- (void)viewDidLoad
{
  [super viewDidLoad];

  layer = [[CALayer alloc] init];
  [self.view.layer addSublayer:layer];
  UIImage *image = [UIImage imageNamed:@"download.jpeg"];
  layer.bounds = CGRectMake(0, 0, image.size.width, image.size.height);
  layer.position = self.view.center;
  layer.contents = (id)image.CGImage;

  [layer setNeedsDisplay];
}

这可能是什么问题？

Answer 1

删除 [layer setNeedsDisplay]; 应该可以纠正该行为。

来自docs (强调):

Calling this method causes the layer to recache its content. This results in the layer potentially calling either the displayLayer: or drawLayer:inContext: method of its delegate. The existing content in the layer’s contents property is removed to make way for the new content.