1、簡(jiǎn)述

因?yàn)橛性谟胐agger2，但是發(fā)現(xiàn)dagger2需要每次創(chuàng)建presenter的時(shí)候都要注入，感覺(jué)很繁瑣，一直在想有沒(méi)好的方法能解決這種問(wèn)題

2、解決問(wèn)題

使用apt自動(dòng)生成presenter工廠類，首先我們創(chuàng)建一個(gè)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的處理要素

注解處理器（AbstractProcess）+代碼處理（javaPoet）+處理器注冊(cè)（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;
  }
}

//實(shí)現(xiàn)統(tǒng)一接口
public class IntanceProcess implements IProcess {
    //類名
    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("@創(chuàng)建presenter工廠類")
                .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, "正在創(chuàng)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淺談

2.2.1 oop

我們主要的代碼都是oop 就是面向?qū)ο?，OOP的精髓是把功能或問(wèn)題模塊化，每個(gè)模塊處理自己的家務(wù)事，但是我們并不能做的很完美，所以就會(huì)出現(xiàn)各個(gè)模塊互相入侵，如log打印等，各個(gè)模塊都需要用到它，使得其他模塊的代碼和日志模塊耦合非常緊密。

2.2.2 aop好處

AOP的目標(biāo)是把這些功能集中起來(lái)，放到一個(gè)統(tǒng)一的地方來(lái)控制和管理。如果說(shuō)，OOP如果是把問(wèn)題劃分到單個(gè)模塊的話，那么AOP就是把涉及到眾多模塊的某一類問(wèn)題進(jìn)行統(tǒng)一管理。比如我們現(xiàn)在做的就是統(tǒng)一使用緩存，緩存所有的presenter,他會(huì)在編譯期間織入我們的代碼

/**
 * 對(duì)presenter對(duì)象進(jìn)行緩存切片
 */
@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);
            //以方法名字和類名做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;
            }
            //執(zhí)行方法
            result = joinPoint.proceed();

            if (result != null) {

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

            }

            return result;
        }
        return null;
    }

}

對(duì)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項(xiàng)目地址,歡迎fork或star，提出寶貴意見(jiàn)https://github.com/AndroidCrow/PresenterFactory