public interface CssResource
extends CssResourceBase

Aggregates and minifies CSS stylesheets. A CssResource represents a regular CSS file with GWT-specific at-rules.

Currently-supported accessor functions:

• String someClassName(); will allow the css class .someClassName to be obfuscated at runtime. The function will return the obfuscated class name.
• <primitive numeric type or String> someDefName(); will allow access to the values defined by @def rules within the CSS file. The defined value must be a raw number, a CSS length, or a percentage value if it is to be returned as a numeric type.

Currently-supported rules:

• @def NAME replacement-expression; .myClass background: NAME; Define a static constant. The replacement expression may be any CSS that would be valid in a property value context. A @def may refer to previously-defined rules, but no forward-references will be honored.
• @eval NAME Java-expression; .myClass background: NAME; Define a constant based on a Java expression.
• @external class-name, class-name, ...; Disable obfuscation for specific class selectors and exclude those class selectors from strictness requirements.
• @if [!]property list of values {ruleBlock} Include or exclude CSS rules based on the value of a deferred-binding property. Also @elif and @else follow the same pattern.
  This might look like @if user.agent ie6 safari ....
• @if (Java-expression) {ruleBlock} Include or exclude CSS rules based on a boolean Java expression.
• @noflip { rules } will suppress the automatic right-to-left transformation applied to the CSS when the module is compiled for an RTL language.
• @sprite .any .selector {gwt-image: "imageResourceFunction";} . The appearance, size, and height of the sprite will be affected by any ImageResource.ImageOptions annotations present on the related ImageResource accessor function. Additional properties may be specified in the rule block.
• @url NAME siblingDataResource; .myClass background: NAME repeat-x; Use a DataResource to generate a url('...'} value.

Currently-supported CSS functions:

• literal("expression") substitutes a property value that does not conform to CSS2 parsing rules. The escape sequences \" and \\ will be replaced with " and \ respectively.
• value("bundleFunction.someFunction[.other[...]]" [, "suffix"]) substitute the value of a sequence of named zero-arg function invocations. An optional suffix will be appended to the return value of the function. The first name is resolved relative to the bundle interface passed to GWT.create(Class). An example:

   .bordersTheSizeOfAnImage {
     border-left: value('leftBorderImageResource.getWidth', 'px') solid blue;
   }
   

Any class selectors that do not correspond with a String accessor method in the return type will trigger a compilation error. This ensures that the CssResource does not contribute any unobfuscated class selectors into the global CSS namespace. Strict mode can be disabled by annotating the ClientBundle method declaration with CssResource.NotStrict, however this is only recommended for interacting with legacy CSS.

Given these interfaces:

 interface MyCss extends CssResource {
   String someClass();
 }
 
 interface MyBundle extends ClientBundle {
  @Source("my.css")
   MyCss css();
 }
 

the source CSS will fail to compile if it does not contain exactly the one class selector defined in the MyCss type.

The @external at-rule can be used in strict mode to indicate that certain class selectors are exempt from the strict semantics. Class selectors marked as external will not be obfuscated and are not required to have string accessor functions. Consider the following example in conjunction with the above MyCss interface:

 @external .foo, .bar;
 .foo .someClass .bar { .... }
 

The resulting CSS would look like:

 .foo .A1234 .bar { .... }
 

If a String foo() method were defined in MyCss, it would return the string value "foo".

The utility tool com.google.gwt.resources.css.InterfaceGenerator can be used to automatically generate a Java interface from a CssResource-compatible CSS file.