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Dart利用注解生成代码

引入依赖

dev_dependencies:
    source_gen: ^1.2.6
    build_runner: '>2.3.0 <4.0.0'

定义注解

import 'package:meta/meta_meta.dart';

///定义注解
@Target({TargetKind.classType})
class JsonGeneratorTest {

  final String name;
  final int age;

  const JsonGeneratorTest(this.name, this.age);
}

解析注解

import 'package:analyzer/dart/element/element.dart';
import 'package:build/src/builder/build_step.dart';
import 'package:source_gen/source_gen.dart';

import 'generator.dart';

/// 注解解析
class TestGenerator extends GeneratorForAnnotation<JsonGeneratorTest> {
  @override
  generateForAnnotatedElement(
      Element element, ConstantReader annotation, BuildStep buildStep) {
    _analyseBuildStep(buildStep);
    _analyseAnnotation(annotation);
    _analyseElement(element);
    return template("_\$${element.name}", "Gen Code");
  }

  void _analyseBuildStep(BuildStep buildStep) {
    print("buildStep:${buildStep.inputId.toString()}\n");
  }

  void _analyseAnnotation(ConstantReader annotation) {
    print("params: ${annotation.read("name")}\n");
    print("params: ${annotation.read("age")}\n");
  }

  void _analyseElement(Element element) {
    print("ElementKind:${element.kind.name}\n");
    switch (element.kind) {
      case ElementKind.CLASS:
        _analyseElementForClass(element);
        break;
      case ElementKind.FUNCTION:
        _analyseElementForMethod(element);
        break;
      default:
        break;
    }
  }

  void _analyseElementForClass(Element element) {
    var e = element as ClassElement;
    e.fields.forEach((element) {
      print("字段:${element.declaration}\n");
    });
    e.methods.forEach((element) {
      print("方法:${element.declaration}");
    });
  }

  void _analyseElementForMethod(Element element) {
    print(
        "方法名称:${element.name},方法参数:${(element as FunctionElement).parameters[0].declaration}");
  }

  template(String className, String content) {
    return """ 
      class ${className}{
        /**
        $content
        */
      }
    """;
  }
}

定义build

import 'package:source_gen/source_gen.dart';
import 'package:build/build.dart' as build;

import 'generator_impl.dart';

///配置builder
build.Builder testBuilder(build.BuilderOptions options) =>
    PartBuilder([TestGenerator()], ".gen.dart");

配置build.yaml

在根目录下新增build.yaml

builders:
  testBuilder:
    import: "package:flutter_demo/generator/test_builder.dart"
    builder_factories: ["testBuilder"]
    build_extensions: {".dart": [".g.part"]}
    auto_apply: root_package
    build_to: source

• testBuilder:builder名称
• Import:要导入的dart类型的build文件
• builder_factories:对应dart类型的build文件中的build.Builder方法
• build_extensions:后缀

使用注解

import 'package:flutter_demo/generator/generator.dart';

///包含foo.gen.dart文件
part 'foo.gen.dart';

///使用注解
@JsonGeneratorTest("张三", 18)
class Foo {
  String name;
  int age;

  Foo(this.name, this.age);
}

生成代码

flutter pub run build_runner build --delete-conflicting-outputs

--delete-conflicting-outputs:删除冲突的文件，可以删除原来生成的文件

执行命令后，会在Foo.dart同目录下生成foo.gen.dart文件