ios 在 CALayer 中添加 UIImage
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add UIImage in CALayer
提问by Adriana Carelli
I must add a UIImageView as subview of MapView. To do this I created a layer above the MapView. In this layer I want to put my image, but I get a white rectangle and nothing else. My image is not visible.
我必须添加一个 UIImageView 作为 MapView 的子视图。为此，我在 MapView 上方创建了一个图层。在这一层我想把我的形象，但我得到一个白色的矩形，没有别的。我的图像不可见。
This is the code:
这是代码：
- (void)viewDidLoad
{
//......
CALayer *layer = [CALayer layer];
layer.backgroundColor = [[UIColor whiteColor] CGColor];
if(UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone)
{
layer.bounds = CGRectMake(self.mapView.bounds.origin.x,
self.mapView.bounds.origin.y, 80, 300);
}
else
{
layer.bounds = CGRectMake(self.mapView.frame.origin.x,
self.mapView.frame.origin.y, 150, 700);
}
layer.contents = (id)[UIImage imageNamed:@"myImage.png"];
//the name is correct but in the output the image is not visible
[[self.mapView layer] addSublayer:layer];
[layer setNeedsDisplay];
}
回答by Suragch
This is a general answer for the sake of future viewers. It is based on the question title rather than the details of the original question.
为了未来的观众，这是一个通用的答案。它基于问题标题而不是原始问题的详细信息。
How to add a UIImage to a CALayer
如何将 UIImage 添加到 CALayer
You can add an image to a view's layersimply by using its contentsproperty:
您可以layer简单地使用其contents属性将图像添加到视图：
myView.layer.contents = UIImage(named: "star")?.cgImage
- Note that the
UIImageneeds to be converted to aCGImage.
- 请注意，
UIImage需要转换为CGImage.
If you wish to add the image in its own layer, you can do it like this:
如果你想在自己的图层中添加图像，你可以这样做：
let myLayer = CALayer()
let myImage = UIImage(named: "star")?.cgImage
myLayer.frame = myView.bounds
myLayer.contents = myImage
myView.layer.addSublayer(myLayer)
Modifying the appearance
修改外观
The above code produces a view like this. The light blue is the UIViewand the dark blue star is the UIImage.
上面的代码产生了这样的视图。浅蓝色是UIView，深蓝色星是UIImage。
As you can see, though, it looks pixelated. This is because the UIImageis smaller than the UIViewso it is being scaled to fill the view, which is the default it you don't specify anything else.
但是，正如您所看到的，它看起来是像素化的。这是因为UIImage小于 ，UIView所以它被缩放以填充视图，这是默认值，您没有指定任何其他内容。
The examples below show variations on the layer's contentsGravityproperty. The code looks like this:
下面的示例显示了图层contentsGravity属性的变化。代码如下所示：
myView.layer.contents = UIImage(named: "star")?.cgImage
myView.layer.contentsGravity = kCAGravityTop
myView.layer.isGeometryFlipped = true
In iOS, you may want to set the isGeometryFlippedpropertyto trueif you are doing anything with top or bottom gravity, otherwise it will be the opposite of what you expect. (Only the gravity is flipped vertically, not the content rendering. If you are having trouble with the content being flipped, see this answer.)
在iOS中，您可能需要设置isGeometryFlipped属性来true，如果你正在做的顶部或底部重力什么，否则这将是你所期望的相反。（只有重力垂直翻转，而不是内容渲染。如果您在翻转内容时遇到问题，请参阅此答案。）
There are two UIViewexamples below for every contentsGravitysetting, one view is larger than the UIImageand the other is smaller. This way you can see the effects of the scaling and gravity.
UIView每个contentsGravity设置下面有两个示例，一个视图大于另一个视图UIImage。通过这种方式，您可以看到缩放和重力的效果。
kCAGravityResize
kCAGravityResize
This is the default.
这是默认设置。
kCAGravityResizeAspect
kCAGravityResizeAspect
kCAGravityResizeAspectFill
kCAGravityResizeAspectFill
kCAGravityCenter
kCAGravityCenter
kCAGravityTop
kCAGravityTop
kCAGravityBottom
kCAGravityBottom
kCAGravityLeft
kCAGravityLeft
kCAGravityRight
kCAGravityRight
kCAGravityTopLeft
kCAGravityTopLeft
kCAGravityTopRight
kCAGravityTopRight
kCAGravityBottomLeft
kCAGravityBottomLeft
kCAGravityBottomRight
kCAGravityBottomRight
Related
有关的
回答by Bastian
it has to be
它一定要是
layer.contents = (id)[UIImage imageNamed:@"myImage.png"].CGImage;
You can only put a CGImage into a layer, not an UIImage directly.
CGImage 只能放入图层，不能直接放入 UIImage。
回答by Adriana Carelli
I removed
我删除了
[layer setNeedsDisplay];
I do not know why, but it works!
我不知道为什么，但它有效！
回答by Soul Clinic
You need to set the frame of the CALayer properly, because the default is CGRectZero.
需要正确设置CALayer的frame，因为默认是CGRectZero。
回答by JonyFang
myView.layer.contents = UIImage(named: "star")?.cgImage
myView.layer.contents = UIImage(named: "star")?.cgImage
