1、简述

因为有在用dagger2，但是发现dagger2需要每次创建presenter的时候都要注入，感觉很繁琐，一直在想有没好的方法能解决这种问题

2、解决问题

使用apt自动生成presenter工厂类，首先我们创建一个apt module
添加如下引用

  compile 'com.squareup:javapoet:1.8.0'
  compile 'com.google.auto.service:auto-service:1.0-rc2'

2.1 APT的处理要素

注解处理器（AbstractProcess）+代码处理（javaPoet）+处理器注册（AutoService）+apt

@AutoService(Processor.class)
@SupportedAnnotationTypes("myapp.apt_lib.apt.InstanceFactory")
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public class AnnotationProcess extends AbstractProcessor {
  public Filer mFiler;
  public Messager mMessager;
  public Elements mElementUtils;

  @Override
  public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnvironment) {
      mFiler = processingEnv.getFiler();
      mMessager = processingEnv.getMessager();
      mElementUtils = processingEnv.getElementUtils();
      new IntanceProcess().process(roundEnvironment, this);
      return false;
  }
}

//实现统一接口
public class IntanceProcess implements IProcess {
    //类名
    private static final String CLASS_NAME = "PresenterFactory";
    //方法名
    private static final String METHOD_NAME = "create";

    @Override
    public void process(RoundEnvironment roundEnv, AnnotationProcess process) {
        
        TypeSpec.Builder tb = TypeSpec.classBuilder(CLASS_NAME)
                .addJavadoc("@创建presenter工厂类")
                .addModifiers(Modifier.PUBLIC, Modifier.FINAL);

        MethodSpec.Builder method = MethodSpec.methodBuilder(METHOD_NAME)
                .addAnnotation(MemoryCache.class)
                .addModifiers(Modifier.PUBLIC, Modifier.STATIC)
                .returns(Object.class)
                .addParameter(Class.class, "clazz")
                .addException(IllegalAccessException.class)
                .addException(InstantiationException.class);

        List<ClassName> list = new ArrayList<>();

        CodeBlock.Builder cb = CodeBlock.builder();

        cb.beginControlFlow("switch(clazz.getSimpleName())");

        for (TypeElement typeElement : ElementFilter.typesIn(roundEnv.getElementsAnnotatedWith(InstanceFactory.class))) {

            process.mMessager.printMessage(Diagnostic.Kind.NOTE, "正在创建" + typeElement.toString());

            if (!Utils.isValidClass(process.mMessager, typeElement)) return;

            ClassName className = ClassName.get(typeElement);

            if (list.contains(className)) continue;

            list.add(className);

            cb.addStatement("case $S: return new $T()",typeElement.getSimpleName(),typeElement);

        }

        cb.addStatement("default: return clazz.newInstance()");

        cb.endControlFlow();

        method.addCode(cb.build());

        tb.addMethod(method.build());

        JavaFile javaFile = JavaFile.builder("myapp.apt.util",tb.build()).build();

        try {
            javaFile.writeTo(process.mFiler);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

}

2.2 Aop浅谈

2.2.1 oop

我们主要的代码都是oop 就是面向对象，OOP的精髓是把功能或问题模块化，每个模块处理自己的家务事，但是我们并不能做的很完美，所以就会出现各个模块互相入侵，如log打印等，各个模块都需要用到它，使得其他模块的代码和日志模块耦合非常紧密。

2.2.2 aop好处

AOP的目标是把这些功能集中起来，放到一个统一的地方来控制和管理。如果说，OOP如果是把问题划分到单个模块的话，那么AOP就是把涉及到众多模块的某一类问题进行统一管理。比如我们现在做的就是统一使用缓存，缓存所有的presenter,他会在编译期间织入我们的代码

/**
 * 对presenter对象进行缓存切片
 */
@Aspect
public class MemoryCacheAspect {

    private static final String POINTCUT_METHOD = "execution(myapp.apt_lib.aop.MemoryCache * *(..))";

    @Pointcut(POINTCUT_METHOD)
    public void methodMemoryCache() {
    }

    @Around("methodMemoryCache()")
    public Object weaveJoinPoint(ProceedingJoinPoint joinPoint) throws Throwable {
        CodeSignature signature = (CodeSignature) joinPoint.getSignature();
        if (signature instanceof MethodSignature) {

            String name = signature.getName();

            MemoryCacheManager memoryCacheManager = MemoryCacheManager.getInstance();

            StringBuffer sb = new StringBuffer();
            sb.append(name);
            //以方法名字和类名做Key
            for (Object o : joinPoint.getArgs()) {
                if (o instanceof Class) {
                    sb.append(((Class) o).getSimpleName());
                }
            }
            String key = sb.toString();
            Object result = memoryCacheManager.get(key);
            if (result != null) {
                return result;
            }
            //执行方法
            result = joinPoint.proceed();

            if (result != null) {

                if (result instanceof Object) memoryCacheManager.put(key, result);

            }

            return result;
        }
        return null;
    }

}

对presenter注解

@InstanceFactory
public class TextPresenter extends BasePresenter {
    public TextPresenter(){}
    public void text(String name){
        Log.d(TextPresenter.class.getName(),name);
    }
    @Override
    public void setView(BaseActivity view) {
    }
}

• GitHub项目地址,欢迎fork或star，提出宝贵意见https://github.com/AndroidCrow/PresenterFactory