本文适合有一定的Dagger2使用基础的同学

前两篇文章我们讲了两种多模块项目怎么使用Dagger2。

发现在每个Activity的onCreate中都需要调一个inject方法NewsComponentHolder.newsComponent.inject(this)

UserComponentHolder.userComponent.inject(this)

其实还可以用dagger2专给android使用的dagger.android来简化这种操作。

先看普通多模块项目

dagger.android的核心思想是在每个Component收集两个MapMap, Provider>> injectorFactoriesWithClassKeys

Map>> injectorFactoriesWithStringKeys

这两个Map定义在AndroidInjectionModule中@Beta

@Module

public abstract class AndroidInjectionModule {

@Multibinds

abstract Map, AndroidInjector.Factory>> classKeyedInjectorFactories();

@Multibinds

abstract Map> stringKeyedInjectorFactories();

private AndroidInjectionModule() {}

}

dagger.android会把把收集到的这两个Map注入到DispatchingAndroidInjector中，dagger.android就是通过这个DispatchingAndroidInjector注入到Activity,Fragment中

怎么收集呢

首先定义一个 xxxBindModule ，将要注入的Activity,fragment用@ContributesAndroidInjector注解

dagger.android会把这些收集到前面的Map中去@Module(includes = [AndroidInjectionModule::class])

abstract class NewsBindModule {

@ContributesAndroidInjector

abstract fun newsActivity(): NewsActivity

}

然后相应的Component的modules加上xxxBindModule,

去掉inject(XXXActivity)这样的一大堆声明方法,干净多了@NewsScope

@Subcomponent(modules = [NewsModule::class, NewsBindModule::class])

interface NewsComponent {

@Subcomponent.Factory

interface Factory {

fun create(): NewsComponent

}

}

之后按照dagger.android用法要让Application实现HasAndroidInjector接口，并注入dispatchingAndroidInjector实例class AppApplication : BaseApplication(), NewsComponentProvider, UserComponentProvider, HasAndroidInjector {

@Inject

lateinit var dispatchingAndroidInjector: DispatchingAndroidInjector

lateinit var appComponent: AppComponent

override fun onCreate() {

super.onCreate()

appComponent = DaggerAppComponent.factory().create(this)

}

override fun provideNewsComponent(): NewsComponent {

return appComponent.newsComponentFactory().create()

}

override fun provideUserComponent(): UserComponent {

return appComponent.userComponentFactory().create()

}

override fun androidInjector(): AndroidInjector {

return dispatchingAndroidInjector

}

}

再在Component加上一个注入到上面Appliction的方法(因为news模块拿不到AppApplication的引用，直接注入到Any好了)@NewsScope

@Subcomponent(modules = [NewsModule::class, NewsBindModule::class])

interface NewsComponent {

@Subcomponent.Factory

interface Factory {

fun create(): NewsComponent

}

fun inject(any: Any)

}

然后在AppApplication中注入class AppApplication : BaseApplication(), NewsComponentProvider, UserComponentProvider {

@Inject

lateinit var dispatchingAndroidInjector: DispatchingAndroidInjector

lateinit var appComponent: AppComponent

override fun onCreate() {

super.onCreate()

appComponent = DaggerAppComponent.factory().create(this)

NewsComponentHolder.newsComponent.inject(this)

}

override fun provideNewsComponent(): NewsComponent {

return appComponent.newsComponentFactory().create()

}

override fun provideUserComponent(): UserComponent {

return appComponent.userComponentFactory().create()

}

override fun androidInjector(): AndroidInjector {

return dispatchingAndroidInjector

}

}

最后在Activity，fragment的onCreate方法中加入AndroidInjection.inject(this),注意要放在super.onCreate(savedInstanceState)前面,我们把这一步放在BaseActivity,BaseFragment里open class BaseActivity : AppCompatActivity() {

override fun onCreate(savedInstanceState: Bundle?) {

AndroidInjection.inject(this)

super.onCreate(savedInstanceState)

}

}

然后Activity只要继承BaseActivity就可以了，不需要写任何注入代码了，像平时使用一样了，想要注入对象的变量加 @Inject就可以了class NewsActivity : BaseActivity() {

@Inject

lateinit var set: Set

override fun onCreate(savedInstanceState: Bundle?) {

super.onCreate(savedInstanceState)

setContentView(R.layout.activity_news)

text.text = set.toString()

}

}

这种写法对于单模块项目没有问题，但是对多模块项目来说这有问题了，上面我们只注入了news模块的，user模块的没有。我们有多个Component,但是这里只有一个dispatchingAndroidInjector，你用哪个Component注入都不全，后面注入的会覆盖前面注入的。所以这里要改造下

从前面我们知道一个Component最终生成一个DispatchingAndroidInjector，多个Component我们把它们都收集起来

我们先定义一个BaseDispatchingInjector,它相当于前面的AppApplication,接收一个Component注入的DispatchingAndroidInjectorclass BaseDispatchingInjector {

@Inject

lateinit var dispatchingAndroidInjector: DispatchingAndroidInjector

}

然后把每个Component里的inject(any: Any)改成inject(baseDispatchingInjector: BaseDispatchingInjector)@NewsScope

@Subcomponent(modules = [NewsModule::class, NewsBindModule::class])

interface NewsComponent {

@Subcomponent.Factory

interface Factory {

fun create(): NewsComponent

}

fun inject(baseDispatchingInjector: BaseDispatchingInjector)

}

@UserScope

@Subcomponent(modules = [UserModule::class, UserBindModule::class])

interface UserComponent {

@Subcomponent.Factory

interface Factory {

fun create(): UserComponent

}

fun inject(baseDispatchingInjector: BaseDispatchingInjector)

}

这样注入val userDispatchingInjector = BaseDispatchingInjector()

UserComponentHolder.userComponent.inject(userDispatchingInjector)

val newsDispatchingInjector = BaseDispatchingInjector()

NewsComponentHolder.newsComponent.inject(newsDispatchingInjector)

这样我们每个模块都得到一个BaseDispatchingInjector,并且里面每个Activity,Fragment对应的Map都注入好了

然后就要定义一个MultiModuleAndroidInjector把每个模块的BaseDispatchingInjector整合到一起成为一个单独的AndroidInjectorclass MultiModuleAndroidInjector : AndroidInjector {

private val injectors = mutableListOf()

fun addInjector(injector: HasDispatchingInjector) {

injectors.add(injector)

}

override fun inject(instance: Any) {

val wasInjected = injectors.any { it.dispatchingAndroidInjector.maybeInject(instance) }

if (!wasInjected) {

throw IllegalArgumentException("injection failed")

}

}

}

这个MultiModuleAndroidInjector在注入的时候会每个BaseDispatchingInjector都去尝试看能不能注入，这样就把所有Component的注解都遍历了

看AppApplication最后实现class AppApplication : BaseApplication(), NewsComponentProvider, UserComponentProvider,

HasAndroidInjector {

lateinit var appComponent: AppComponent

private val multiModuleAndroidInjector = MultiModuleAndroidInjector()

override fun onCreate() {

super.onCreate()

appComponent = DaggerAppComponent.factory().create(this)

val userDispatchingInjector = BaseDispatchingInjector()

UserComponentHolder.userComponent.inject(userDispatchingInjector)

multiModuleAndroidInjector.addInjector(userDispatchingInjector)

val newsDispatchingInjector = BaseDispatchingInjector()

NewsComponentHolder.newsComponent.inject(newsDispatchingInjector)

multiModuleAndroidInjector.addInjector(newsDispatchingInjector)

}

override fun provideNewsComponent(): NewsComponent {

return appComponent.newsComponentFactory().create()

}

override fun provideUserComponent(): UserComponent {

return appComponent.userComponentFactory().create()

}

override fun androidInjector(): AndroidInjector {

return multiModuleAndroidInjector

}

}