USS 属性类型

内置属性与自定义属性

使用 USS 时，可为内置的 VisualElement 属性或 UI 代码中的自定义属性指定值。

In addition of reading their values from USS files, you can assign built-in property values in C#, using the C# properties of VisualElement. Values assigned in C# override values from a Unity style sheet (USS).

可使用自定义属性 来扩展 USS。自定义 USS 属性需要 -- 前缀。

属性值

本节列出了支持的类型。

长度

UI 工具包支持像素 (px) 和百分比 (%) 作为长度的度量单位。像素值是绝对值，而百分比通常相对于元素父级。

例如：

• width:200px; 表示宽度为 200 像素。
• width:50%; 表示宽度为父元素宽度的一半。

It’s important to specify the unit of measurement. If you do not specify a unit of measurement, UI Toolkit assumes that the property value is expressed in pixels.

注意：0 是一个不需要度量单位的特殊值。

数值

数值表示为浮点或整数字面值。例如：flex:1.0。

关键字

某些内置属性支持特定关键字。关键字提供描述性名称而不是数字。例如：position:absolute。所有属性都支持 initial 全局关键字，该关键字将属性重置为默认值。请参阅支持的属性以查看关键字的列表。

颜色

UI 工具包支持以下字面颜色值和函数：

• 十六进制值：#FFFF00（rgba，每个通道一个字节）、#0F0 (rgb)
• RGB 函数：rgb(255, 255, 0)
• RGBA 函数：rgba(255, 255, 0, 1.0)
• 颜色关键字：blue、transparent

资源

You can reference project assets such as fonts and textures from your USS files. For example, you might reference a texture to use as the background image for an element.

To reference an asset, you can use either the url() function or the resource() function. Referenced Assets are resolved when the style sheet is imported.

For example, the style declaration below uses the resource() function to reference a texture asset named img.png in the Images directory, and specify it as the background image.

`background-image: resource("Images/img.png");

Unity recommends using url() function in most cases. However, the resource() function supports automatically loading different versions of image assets for different screen densities.

Referencing assets with the url function

When you reference an asset with the url() function, the path you specify can be relative or absolute:

• Relative paths must be relative to the folder that contains the USS file that references the asset.
• Absolute paths are relative to the project.

The path must include the file extension.

For example, let’s say your project has a USS folder that contains all of your style sheets, and a Resources folder that contains all of your image assets.

Assets
  └─ Editor
      └─ Resources
      └─ USS

To reference an image named thumb.png, you can use one of the following paths:

Relative path	Absolute path
url("../Resources/thumb.png")	url("/Assets/Editor/Resources/thumb.png") url("project:/Assets/Editor/Resources/thumb.png") url("project:///Assets/Editor/Resources/thumb.png")

Referencing assets with the resource function

The resource() function can reference assets in Unity’s resource folders (Resources and Editor Default Resources). You reference an asset by name.

• If the file is in the Editor Default Resources Resources folder, you must include the file extension.
• If the file is in the Resources folder, you must not include the file extension.

例如：

Path to file	Reference syntax
Assets/Resources/Images/my-image.png	resource("Images/my-image")
Assets/Editor Default Resources/Images/my-image.png	resource("Images/default-image.png")

Referencing image assets for High DPI/Retina screens

If you need to support screens with different screen densities (DPI), the resource() function allows you to load the correct versions of texture assets automatically.

You have to:

• Make sure that the high DPI versions of your textures have a @2x suffix in their file names. For example the high DPI version of myimage.png should be myimage@2x.png
• Place the regular and high DPI versions of the texture assets in the same project folder.

When Unity loads the asset, it automatically chooses the correct version for the current screen DPI.

For example, if you use resource("myimage") in USS, Unity loads either Resources/myimage.png or Resources/myimage@2x.png.

字符串

使用引号指定字符串值。例如：--my-property: "foo"。