一、新建项目,新增和业务逻辑相关的类。
1、新增Test01类:
public class Test1 {
public Test1() {
}
public void sayHelloWorld() {
Log.d("Test1", "Hello World");
}
}
这个类构造方法无参数,只有一个sayHelloWorld方法,在控制台打印日志信息Hello World。
2、新增Test02类:
public class Test2 {
private Context context;
public Test2(Context context) {
this.context = context;
}
public void sayHelloWorld() {
if(context != null){
Log.d("Test2", "Hello World");
}
}
}
这个类和Test01相比,构造方法新增了一个Context类型的参数,且sayHelloWorld会根据context是否为空来决定是否打印日志信息Hello World。
3、新增Test03类:
public class Test3 {
private Context context;
@Inject
public Test3(Context context) {
this.context = context;
}
public void sayHelloWorld() {
if (context != null) {
Log.d("Test3", "Hello World");
}
}
}
这个类和Test02相比,只是多了一个@Inject注解。
4、MainActivity类:
public class MainActivity extends AppCompatActivity {
@Inject
Test1 test1;
@Inject
Test2 test2;
@Inject
Test3 test3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
test1.sayHelloWorld();
test2.sayHelloWorld();
test3.sayHelloWorld();
}
}
把上面新增的Test1 、Test2、Test3作为MainActivity的属性变量,添加@Inject注解,然后再onCreate方法中分别调用它们的sayHelloWorld方法,看看是否能够在控制台打印出来日志信息。现在如果直接这么调用,肯定会报错,在调用三个Test对象的sayHelloWorld方法之前,我们需要做一些辅助操作,让Dagger2框架知道如何进行把MainActivity和Test01,Test02,Test03关联起来,并完成依赖注入。
二、新增和业务逻辑相关、和Dagger2依赖注入有关的类:
1、新增AndroidModule类:
@Module
public class AndroidModule {
private final Context context;
public AndroidModule(Context context) {
this.context = context;
}
@Provides
@Singleton
Context getContext() {
return context;
}
@Provides
@Singleton
Test1 provideTest1() {
return new Test1();
}
@Provides
@Singleton
Test2 provideTest2() {
return new Test2(context);
}
}
AndroidModule类首先是被@Module注解标记;然后此类的构造方法需要传入Context类型的参数;有三个内部方法,getContext返回Context,provideTest1方法返回Test1实例对象,provideTest2方法返回Test2实例对象,这三个方法刚返回的三个实例对象,后续我们是可以在其他地方直接拿到的。
2、新增MainActivityComponent类:
@Singleton
@Component(modules = AndroidModule.class)
public interface MainActivityComponent{
void inject(MainActivity mainActivity);
}
此类被@Singleton和@Component注解标记,@Singleton会让Dagger2再生成这个接口的实现类的时候,该是将类的获取方式将会是个单例模式,@Component是告诉Dagger2这个类是个连接器,由于我们需要在MainActivity类中进行依赖注入,所以这里提供了inject(MainActivity mainActivity)供MainActivity来调用,以达到通过依赖注入的方式获取Test1、Test2、Test3这些类的实例对象需求。
3、修改MainActivity类的onCreate方法:
public class MainActivity extends AppCompatActivity {
@Inject
Test1 test1;
@Inject
Test2 test2;
@Inject
Test3 test3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//调用下面的代码实现依赖注入
DaggerMainActivityComponent.builder()
.androidModule(new AndroidModule(this))
.build().inject(this);
test1.sayHelloWorld();
test2.sayHelloWorld();
test3.sayHelloWorld();
}
}
4、成功运行代码,日志信息如下所示:
2022-11-12 15:58:03.586 4531-4531 Test1 com.example.dagger2application D Hello World
2022-11-12 15:58:03.586 4531-4531 Test2 com.example.dagger2application D Hello World
2022-11-12 15:58:03.586 4531-4531 Test3 com.example.dagger2application D Hello World
三、查看使用Dagger2新增了那些临时类
打开build/generated/ap_generaed_sources/debug/out/com/example/dagger2application目录:
可以发现该目录新增了六个类。
1、AndroidModule_GetApplicationContextFactory类:
public final class AndroidModule_GetApplicationContextFactory implements Factory<Context> {
private final AndroidModule module;
public AndroidModule_GetApplicationContextFactory(AndroidModule module) {
this.module = module;
}
@Override
public Context get() {
return getApplicationContext(module);
}
public static AndroidModule_GetApplicationContextFactory create(AndroidModule module) {
return new AndroidModule_GetApplicationContextFactory(module);
}
public static Context getApplicationContext(AndroidModule instance) {
return Preconditions.checkNotNullFromProvides(instance.getApplicationContext());
}
}
2、AndroidModule_ProvideTest1Factory类:
public final class AndroidModule_ProvideTest1Factory implements Factory<Test1> {
private final AndroidModule module;
public AndroidModule_ProvideTest1Factory(AndroidModule module) {
this.module = module;
}
@Override
public Test1 get() {
return provideTest1(module);
}
public static AndroidModule_ProvideTest1Factory create(AndroidModule module) {
return new AndroidModule_ProvideTest1Factory(module);
}
public static Test1 provideTest1(AndroidModule instance) {
return Preconditions.checkNotNullFromProvides(instance.provideTest1());
}
}
3、AndroidModule_ProvideTest2Factory类:
public final class AndroidModule_ProvideTest2Factory implements Factory<Test2> {
private final AndroidModule module;
public AndroidModule_ProvideTest2Factory(AndroidModule module) {
this.module = module;
}
@Override
public Test2 get() {
return provideTest2(module);
}
public static AndroidModule_ProvideTest2Factory create(AndroidModule module) {
return new AndroidModule_ProvideTest2Factory(module);
}
public static Test2 provideTest2(AndroidModule instance) {
return Preconditions.checkNotNullFromProvides(instance.provideTest2());
}
}
4、DaggerMainActivityComponent类:
public final class DaggerMainActivityComponent {
private DaggerMainActivityComponent() {
}
public static Builder builder() {
return new Builder();
}
public static final class Builder {
private AndroidModule androidModule;
private Builder() {
}
public Builder androidModule(AndroidModule androidModule) {
this.androidModule = Preconditions.checkNotNull(androidModule);
return this;
}
public MainActivityComponent build() {
Preconditions.checkBuilderRequirement(androidModule, AndroidModule.class);
return new MainActivityComponentImpl(androidModule);
}
}
private static final class MainActivityComponentImpl implements MainActivityComponent {
private final MainActivityComponentImpl mainActivityComponentImpl = this;
private Provider<Test1> provideTest1Provider;
private Provider<Test2> provideTest2Provider;
private Provider<Context> getApplicationContextProvider;
private MainActivityComponentImpl(AndroidModule androidModuleParam) {
initialize(androidModuleParam);
}
private Test3 test3() {
return new Test3(getApplicationContextProvider.get());
}
@SuppressWarnings("unchecked")
private void initialize(final AndroidModule androidModuleParam) {
this.provideTest1Provider = DoubleCheck.provider(AndroidModule_ProvideTest1Factory.create(androidModuleParam));
this.provideTest2Provider = DoubleCheck.provider(AndroidModule_ProvideTest2Factory.create(androidModuleParam));
this.getApplicationContextProvider = DoubleCheck.provider(AndroidModule_GetApplicationContextFactory.create(androidModuleParam));
}
@Override
public void inject(MainActivity mainActivity) {
injectMainActivity(mainActivity);
}
private MainActivity injectMainActivity(MainActivity instance) {
MainActivity_MembersInjector.injectTest1(instance, provideTest1Provider.get());
MainActivity_MembersInjector.injectTest2(instance, provideTest2Provider.get());
MainActivity_MembersInjector.injectTest3(instance, test3());
return instance;
}
}
}
5、MainActivity_MembersInjector类:
public final class MainActivity_MembersInjector implements MembersInjector<MainActivity> {
private final Provider<Test1> test1Provider;
private final Provider<Test2> test2Provider;
private final Provider<Test3> test3Provider;
public MainActivity_MembersInjector(Provider<Test1> test1Provider, Provider<Test2> test2Provider,
Provider<Test3> test3Provider) {
this.test1Provider = test1Provider;
this.test2Provider = test2Provider;
this.test3Provider = test3Provider;
}
public static MembersInjector<MainActivity> create(Provider<Test1> test1Provider,
Provider<Test2> test2Provider, Provider<Test3> test3Provider) {
return new MainActivity_MembersInjector(test1Provider, test2Provider, test3Provider);
}
@Override
public void injectMembers(MainActivity instance) {
injectTest1(instance, test1Provider.get());
injectTest2(instance, test2Provider.get());
injectTest3(instance, test3Provider.get());
}
@InjectedFieldSignature("com.example.dagger2application.MainActivity.test1")
public static void injectTest1(MainActivity instance, Test1 test1) {
instance.test1 = test1;
}
@InjectedFieldSignature("com.example.dagger2application.MainActivity.test2")
public static void injectTest2(MainActivity instance, Test2 test2) {
instance.test2 = test2;
}
@InjectedFieldSignature("com.example.dagger2application.MainActivity.test3")
public static void injectTest3(MainActivity instance, Test3 test3) {
instance.test3 = test3;
}
}
6、Test3_Factory类:
public final class Test3_Factory implements Factory<Test3> {
private final Provider<Context> contextProvider;
public Test3_Factory(Provider<Context> contextProvider) {
this.contextProvider = contextProvider;
}
@Override
public Test3 get() {
return newInstance(contextProvider.get());
}
public static Test3_Factory create(Provider<Context> contextProvider) {
return new Test3_Factory(contextProvider);
}
public static Test3 newInstance(Context context) {
return new Test3(context);
}
}
四、总结
1、结合Dagger2框架新增的六个类我们可以发现,在MainActivity的onCreate方法中,Dagger2框架实现依赖注入的流程如下所示:
2、MainActivity的onCreate方法关键代码:
public class MainActivity extends AppCompatActivity {
...代码省略...
@Override
protected void onCreate(Bundle savedInstanceState) {
...代码省略...
//调用下面的代码实现依赖注入
DaggerMainActivityComponent.builder()
.androidModule(new AndroidModule(this))
.build().inject(this);
...代码省略...
}
}
3、DaggerMainActivityComponent的builder方法关键代码:
public final class DaggerMainActivityComponent {
public static Builder builder() {
return new Builder();
}
}
4、DaggerMainActivityComponent内部类Builder的androidModule方法和build方法关键代码:
public final class DaggerMainActivityComponent {
public static final class Builder {
private AndroidModule androidModule;
...代码省略...
public Builder androidModule(AndroidModule androidModule) {
this.androidModule = Preconditions.checkNotNull(androidModule);
return this;
}
public MainActivityComponent build() {
Preconditions.checkBuilderRequirement(androidModule, AndroidModule.class);
return new MainActivityComponentImpl(androidModule);
}
}
}
5、DaggerMainActivityComponent内部类MainActivityComponentImpl的inject方法:
public final class DaggerMainActivityComponent{
private static final class MainActivityComponentImpl implements MainActivityComponent {
private final MainActivityComponentImpl mainActivityComponentImpl = this;
private Provider<Test1> provideTest1Provider;//可以获取Test1实例
private Provider<Test2> provideTest2Provider;//可以获取Test3实例
private Provider<Context> getApplicationContextProvider;//可以获取Context实例
private MainActivityComponentImpl(AndroidModule androidModuleParam) {
initialize(androidModuleParam);
}
//创建Test3实例
private Test3 test3() {
return new Test3(getApplicationContextProvider.get());
}
//这个方法很关键,会对provideTest1Provider、provideTest2Provider、getApplicationContextProvider进行初始化
@SuppressWarnings("unchecked")
private void initialize(final AndroidModule androidModuleParam) {
this.provideTest1Provider = DoubleCheck.provider(AndroidModule_ProvideTest1Factory.create(androidModuleParam));
this.provideTest2Provider = DoubleCheck.provider(AndroidModule_ProvideTest2Factory.create(androidModuleParam));
this.getApplicationContextProvider = DoubleCheck.provider(AndroidModule_GetApplicationContextFactory.create(androidModuleParam));
}
@Override
public void inject(MainActivity mainActivity) {
injectMainActivity(mainActivity);
}
private MainActivity injectMainActivity(MainActivity instance) {
MainActivity_MembersInjector.injectTest1(instance, provideTest1Provider.get());
MainActivity_MembersInjector.injectTest2(instance, provideTest2Provider.get());
MainActivity_MembersInjector.injectTest3(instance, test3());
return instance;
}
}
}
inject会进一步调用injectMainActivity方法,injectMainActivity内部分别调用MainActivity_MembersInjector的injectTest1、injectTest2、injectTest3方法,对MainActivity中的test1、test2、test3进行赋值。
6、MainActivity_MembersInjector的injectTest1、injectTest2、injectTest3方法如下所示
public final class MainActivity_MembersInjector implements MembersInjector<MainActivity> {
...代码省略...
@InjectedFieldSignature("com.example.dagger2application.MainActivity.test1")
public static void injectTest1(MainActivity instance, Test1 test1) {
instance.test1 = test1;
}
@InjectedFieldSignature("com.example.dagger2application.MainActivity.test2")
public static void injectTest2(MainActivity instance, Test2 test2) {
instance.test2 = test2;
}
@InjectedFieldSignature("com.example.dagger2application.MainActivity.test3")
public static void injectTest3(MainActivity instance, Test3 test3) {
instance.test3 = test3;
}
}
以上就是在MainActivity中,Dagger2实现依赖注入的整个流程。