| <html devsite><head> |
| <title>导出常量</title> |
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| <p>在接口不兼容 Java（例如由于使用联合类型而不兼容 Java）的情况下，可能仍需将常量（枚举值）导出到 Java 环境。这种情况需要用到 <code>hidl-gen -Ljava-constants |
| …</code>，它会将已添加注释的枚举声明从软件包的接口文件提取出来，并生成一个名为 <code>[PACKAGE-NAME]-V[PACKAGE-VERSION]-java-constants</code> 的 java 库。请为每个要导出的枚举声明添加注释，如下所示：</p> |
| |
| <pre class="prettyprint"> |
| @export |
| enum Foo : int32_t { |
| SOME_VALUE, |
| SOME_OTHER_VALUE, |
| }; |
| </pre> |
| |
| <p>如有必要，这一类型导出到 Java 环境时所使用的名称可以不同于接口声明中选定的名称，方法是添加注释参数 <code>name</code>：</p> |
| |
| <pre class="prettyprint"> |
| @export(name="JavaFoo") |
| enum Foo : int32_t { |
| SOME_VALUE, |
| SOME_OTHER_VALUE, |
| }; |
| </pre> |
| |
| <p>如果依据 Java 惯例或个人偏好需要将一个公共前缀添加到枚举类型的值，请使用注释参数 <code>value_prefix</code>：</p> |
| |
| <pre class="prettyprint"> |
| // File "types.hal". |
| |
| package android.hardware.bar@1.0; |
| |
| @export(name="JavaFoo", value_prefix="JAVA_") |
| enum Foo : int32_t { |
| SOME_VALUE, |
| SOME_OTHER_VALUE, |
| }; |
| </pre> |
| |
| <p>生成的 Java 类如下所示：</p> |
| |
| <pre class="prettyprint"> |
| package android.hardware.bar.V1_0; |
| |
| public class Constants { |
| public final class JavaFoo { |
| public static final int JAVA_SOME_VALUE = 0; |
| public static final int JAVA_SOME_OTHER_VALUE = 1; |
| }; |
| }; |
| </pre> |
| |
| <p>最后，针对 <code>types.hal</code> 中声明的枚举类型的 Java 类型声明将划分到指定软件包中的类 <code>Constants</code> 内。声明为接口子级的枚举类型将划分到该接口的 Java 类声明下。</p> |
| |
| </body></html> |
