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dagger2

2015-11-18 13:49:32   0  举报

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AI智能生成

Dagger2

IOC Dagger

作者其他创作

大纲/内容

依赖注入

控制反转原则

应用流程取决于运行时构建的对象图

通过抽象定义出对象交互使动态流成为可能

运行时绑定的途径有依赖注入或服务加载

依赖注入的诱惑

外部配置和注入,组件可重用

协作是定义在抽象层面的,修改对象的实现并不需要改基本代码.在一个地方实例化就可以隔离和解耦

依赖可以注入到组件,好测试(注入mock对象)

对象和协作者无需知晓创建及生命周期(依赖注入框架接管)

JSR-330

Java依赖注入

一套类注入的注释标准

重用性最大化

可测性最大化

维护性最大化

实现

Dagger2

Dagger1

Guice

Dagger1

原理

多点注入:依赖注入

多次绑定:提供依赖

多模块:一个功能由一套绑定实现

多个对象图:用一套模块实现一个范围

特点

编译时绑定

用反射来构建依赖图(不用在对象实例化)

运行时处理

问题

效率损耗

调试难

Dagger2

简介

Google在Dagger1上引出

加入google的AutoValue项目

最初想借代码生成来解决问题

进步与代价

无反射:编译时验证,配置和预处理

好调试跟踪:完整具体的调用栈

高效:google自称13%的效率提升

代码安全:方法派遣,高仿手写代码

灵活性降低:不用反射,缺少动态机制

依赖注入

概念

@Inject, 请求依赖, Dagger据此构造被注解的类和成员实例,已满足依赖

@Module,提供依赖的类,可分解,可组合,Dagger在此找依赖

@Provide,在module里的方法前,Dagger据此知道想构造和提供的依赖项

@Component,桥接@Inject和@Module

@Scope,自定义Scope可以定义注入对象的粒度,如@PerActivity, @PerFragment, @PerUser

@Qualifier, 补充说明类的类型,如对Context可用@ForApplication, @ForActivity

代码

build.gradle

apply plugin: 'com.neenbedankt.android-apt' buildscript { repositories { jcenter() } dependencies { classpath 'com.neenbedankt.gradle.plugins:android-apt:1.4' } } android { ... } dependencies { apt 'com.google.dagger:dagger-compiler:2.0' compile 'com.google.dagger:dagger:2.0' ... }

编译器, 运行库, apt插件

初始化对象

@Override void initializePresenter() { // All this dependency initialization could have been avoided by using a // dependency injection framework. But in this case this is used this way for // LEARNING EXAMPLE PURPOSE. ThreadExecutor threadExecutor = JobExecutor.getInstance(); PostExecutionThread postExecutionThread = UIThread.getInstance(); JsonSerializer userCacheSerializer = new JsonSerializer(); UserCache userCache = UserCacheImpl.getInstance(getActivity(), userCacheSerializer, FileManager.getInstance(), threadExecutor); UserDataStoreFactory userDataStoreFactory = new UserDataStoreFactory(this.getContext(), userCache); UserEntityDataMapper userEntityDataMapper = new UserEntityDataMapper(); UserRepository userRepository = UserDataRepository.getInstance(userDataStoreFactory, userEntityDataMapper); GetUserDetailsUseCase getUserDetailsUseCase = new GetUserDetailsUseCaseImpl(userRepository, threadExecutor, postExecutionThread); UserModelDataMapper userModelDataMapper = new UserModelDataMapper(); this.userDetailsPresenter = new UserDetailsPresenter(this, getUserDetailsUseCase, userModelDataMapper); }

本类需要知道太多对象创建和提供依赖的边角代码

依赖注入的方案

依赖图:Application Component

Application Module @Provide @Singleton

Activity Component

Activity Module @Provide @PerActivity

User Component

User Module @Provide @PerActivity

详解

Application Component,全应用生命周期的component,注入AndroidApplication和BseActivity类

@Singleton // Constraints this component to one-per-application or unscoped bindings. @Component(modules = ApplicationModule.class) public interface ApplicationComponent { void inject(BaseActivity baseActivity); //Exposed to sub-graphs. Context context(); ThreadExecutor threadExecutor(); PostExecutionThread postExecutionThread(); UserRepository userRepository(); }

@Singleton,应用内唯一component

module中的类必须明确向外暴露,否则不可见

Application Module, 提供全应用周期的对象

@Module public class ApplicationModule { private final AndroidApplication application; public ApplicationModule(AndroidApplication application) { this.application = application; } @Provides @Singleton Context provideApplicationContext() { return this.application; } @Provides @Singleton Navigator provideNavigator() { return new Navigator(); } @Provides @Singleton ThreadExecutor provideThreadExecutor(JobExecutor jobExecutor) { return jobExecutor; } @Provides @Singleton PostExecutionThread providePostExecutionThread(UIThread uiThread) { return uiThread; } @Provides @Singleton UserCache provideUserCache(UserCacheImpl userCache) { return userCache; } @Provides @Singleton UserRepository provideUserRepository(UserDataRepository userDataRepository) { return userDataRepository; } }

注入应用内全局对象, @Provide都带上@Singleton

Activity Component,Activity生命周期component

@PerActivity @Component(dependencies = ApplicationComponent.class, modules = ActivityModule.class) public interface ActivityComponent { //Exposed to sub-graphs. Activity activity(); }

@PerActivity自定义,activity周期

@Scope @Retention(RUNTIME) public @interface PerActivity {}

能activity对象构建是注入

可在Activity范围内使用singleton模式

这些对象只在Activity里用,全局对象图保持清晰

Activity Module: 暴露activity给依赖图

@Module public class ActivityModule { private final Activity activity; public ActivityModule(Activity activity) { this.activity = activity; } @Provides @PerActivity Activity activity() { return this.activity; } }

使用activity作为context的fragment

User Component: 扩展自AcitvityComponent

@PerActivity @Component(dependencies = ApplicationComponent.class, modules = {ActivityModule.class, UserModule.class}) public interface UserComponent extends ActivityComponent { void inject(UserListFragment userListFragment); void inject(UserDetailsFragment userDetailsFragment); }

@PerActivity,activity生命周期,注入用户相关fragments

ActivityModule已经暴露activity context, 子modules不再做

User Module:用户相关的协作对象

@Module public class UserModule { @Provides @PerActivity GetUserListUseCase provideGetUserListUseCase(GetUserListUseCaseImpl getUserListUseCase) { return getUserListUseCase; } @Provides @PerActivity GetUserDetailsUseCase provideGetUserDetailsUseCase(GetUserDetailsUseCaseImpl getUserDetailsUseCase) { return getUserDetailsUseCase; } }

user的use cases, 取列表,取详情

注入依赖及绑定依赖顺序

构造函数注入:类的构造函数前加@Inject

成员对象注入:非私有成员对象前加@Inject

方法注入:方法前加@Inject

实例

BaseActivity:Navigator

public abstract class BaseActivity extends Activity { @Inject Navigator navigator; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); this.getApplicationComponent().inject(this); } protected ApplicationComponent getApplicationComponent() { return ((AndroidApplication)getApplication()).getApplicationComponent(); } protected ActivityModule getActivityModule() { return new ActivityModule(this); } }

成员注入,ApplicationModule显式提供依赖项

onCreate里调用getApplicationComponent()后inject注入

Application对象初始化ApplicationComponent

Activity-Fragment

activity范围UserComponent注入UserDetailsFragment,存在UserDetilsActivity里

private UserComponent userComponent; private void initializeInjector() { this.userComponent = DaggerUserComponent.builder() .applicationComponent(getApplicationComponent()) .activityModule(getActivityModule()) .build(); }

Dagger实现component并以Dagger作为命名前缀,组合的component所以传入所有依赖的component和module参数

@Override public UserComponent getComponent() { return userComponent; }

为满足Fragment的依赖,提供接口

@Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); this.getComponent.inject(this); }

Fragment里调用Component的inject传入fragment参数

HasComponent接口类

public interface HasComponent { C getComponent(); }

BaseFragment类

@SuppressWarnings("unchecked") protected C getComponent(Class componentType) { return componentType.cast(((HasComponent)getActivity()).getComponent()); }

Dagger2生成代码

DaggerApplicationComponent实现ApplicationComponent