dagger2

Dagger2详解

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

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

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

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

好调试跟踪:完整具体的调用栈

高效:google自称13%的效率提升

概念

代码

build.gradle

apply plugin: 'com.neenbedankt.android-apt'\u00A0buildscript {\u00A0 repositories {\u00A0 \u00A0 jcenter()\u00A0 }\u00A0 dependencies {\u00A0 \u00A0 classpath 'com.neenbedankt.gradle.plugins:android-apt:1.4'\u00A0 }}\u00A0android {\u00A0 ...}\u00A0dependencies {\u00A0 apt 'com.google.dagger:dagger-compiler:2.0'\u00A0 compile 'com.google.dagger:dagger:2.0'\u00A0\u00A0\u00A0 ...}

初始化对象

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

@Singleton // Constraints this component to one-per-application or unscoped bindings.@Component(modules = ApplicationModule.class)public interface ApplicationComponent {\u00A0 void inject(BaseActivity baseActivity);\u00A0\u00A0 //Exposed to sub-graphs.\u00A0 Context context();\u00A0 ThreadExecutor threadExecutor();\u00A0 PostExecutionThread postExecutionThread();\u00A0 UserRepository userRepository();}

@Modulepublic class ApplicationModule {\u00A0 private final AndroidApplication application;\u00A0\u00A0 public ApplicationModule(AndroidApplication application) {\u00A0 \u00A0 this.application = application;\u00A0 }\u00A0\u00A0 @Provides @Singleton Context provideApplicationContext() {\u00A0 \u00A0 return this.application;\u00A0 }\u00A0\u00A0 @Provides @Singleton Navigator provideNavigator() {\u00A0 \u00A0 return new Navigator();\u00A0 }\u00A0\u00A0 @Provides @Singleton ThreadExecutor provideThreadExecutor(JobExecutor jobExecutor) {\u00A0 \u00A0 return jobExecutor;\u00A0 }\u00A0\u00A0 @Provides @Singleton PostExecutionThread providePostExecutionThread(UIThread uiThread) {\u00A0 \u00A0 return uiThread;\u00A0 }\u00A0\u00A0 @Provides @Singleton UserCache provideUserCache(UserCacheImpl userCache) {\u00A0 \u00A0 return userCache;\u00A0 }\u00A0\u00A0 @Provides @Singleton UserRepository provideUserRepository(UserDataRepository userDataRepository) {\u00A0 \u00A0 return userDataRepository;\u00A0 }}

@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

Activity Module: 暴露activity给依赖图

@Modulepublic class ActivityModule {\u00A0 private final Activity activity;\u00A0\u00A0 public ActivityModule(Activity activity) {\u00A0 \u00A0 this.activity = activity;\u00A0 }\u00A0\u00A0 @Provides @PerActivity Activity activity() {\u00A0 \u00A0 return this.activity;\u00A0 }}

使用activity作为context的fragment

User Component: 扩展自AcitvityComponent

User Module:用户相关的协作对象

@Modulepublic class UserModule {\u00A0 @Provides @PerActivity GetUserListUseCase provideGetUserListUseCase(GetUserListUseCaseImpl getUserListUseCase) {\u00A0 \u00A0 return getUserListUseCase;\u00A0 }\u00A0\u00A0 @Provides @PerActivity GetUserDetailsUseCase provideGetUserDetailsUseCase(GetUserDetailsUseCaseImpl getUserDetailsUseCase) {\u00A0 \u00A0 return getUserDetailsUseCase;\u00A0 }}

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 {\u00A0\u00A0 @Inject Navigator navigator;\u00A0\u00A0 @Override\u00A0 protected void onCreate(Bundle savedInstanceState) {\u00A0 \u00A0 super.onCreate(savedInstanceState);\u00A0 \u00A0 this.getApplicationComponent().inject(this);\u00A0 }\u00A0\u00A0 protected ApplicationComponent getApplicationComponent() {\u00A0 \u00A0 return ((AndroidApplication)getApplication()).getApplicationComponent();\u00A0 }\u00A0\u00A0 protected ActivityModule getActivityModule() {\u00A0 \u00A0 return new ActivityModule(this);\u00A0 }}

onCreate里调用getApplicationComponent()后inject注入

Application对象初始化ApplicationComponent

Activity-Fragment

private UserComponent userComponent;private void initializeInjector() {\u00A0 this.userComponent = DaggerUserComponent.builder()\u00A0 \u00A0 \u00A0 .applicationComponent(getApplicationComponent())\u00A0 \u00A0 \u00A0 .activityModule(getActivityModule())\u00A0 \u00A0 \u00A0 .build();}

@Override public UserComponent getComponent() {\u00A0 return userComponent;}

@Override public void onActivityCreated(Bundle savedInstanceState) {\u00A0 super.onActivityCreated(savedInstanceState);\u00A0 this.getComponent.inject(this);}

Fragment里调用Component的inject传入fragment参数

HasComponent接口类

public interface HasComponent {\u00A0 C getComponent();}

BaseFragment类

@SuppressWarnings(\"unchecked\")protected C getComponent(Class componentType) {\u00A0 return componentType.cast(((HasComponent)getActivity()).getComponent());}

Dagger2生成代码

DaggerApplicationComponent实现ApplicationComponent