IOC（Inversion of Control）
是一中设计思想，解决业务之间的解耦，是将业务需要的对象交给容器去创建管理（new），而不是传统new获取。
场景：Class-A 中用到了 Class-B中的对象b，一般传统情况下，需要A的代码中显示的new对象或者隐身传递参数，才能调用b，那么用IOC依赖注入的方式，可以把Class-B依赖注入到一个Container的容器里面，这样Class-A或者其他Class-X都是可以通过容器获取对象b。
IOC模型
在Android有俩个常用的ioc对象框架分别为 Dagger2 和 Hilt
Dagger2
Dagger2 - Github Dagger2是基于Java注解并且在编译期完成的依赖注入，在编译阶段通过APT利用注解处理器来生成java代码
既然是ioc那么就需要：依赖提供方、依赖注入容器（桥梁）、依赖需求放。
Dagger2：
- @Module 注解提供方
- @Component 依赖同期
- @Inject 注解变量对象需求方
- @dependencies 组合容器，让多个容器组合成一个容器
- @Provides 构造参数
- @Singleton 单利模式
- @Lazy
懒加载需求，先需要通过 get()获取对象函数
implementation 'com.google.dagger:dagger:2.30.1'
annotationProcessor 'com.google.dagger:dagger-compiler:2.30.1'
@Module
package com.example.dagger2app.object;
import dagger.Module;
import dagger.Provides;
//注册module提供方
@Module
public class HttpObject {
private String url;
public HttpObject() {
}
public HttpObject(String url) {
this.url = url;
}
// @Provides
// public HttpObject providesHttpObject() {
// return new HttpObject();
// }
//构造Provides 需要返回当前对象， + 传参
@Provides
public HttpObject providesHttpObject(String url) {
return new HttpObject(url);
}
//构造参数这里也需要+@Provides
@Provides
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
}
package com.example.dagger2app.object;
import dagger.Module;
import dagger.Provides;
@Module
public class DbObject {
private String name = "lss";
private int age = 20;
public DbObject() {
}
@Provides
public DbObject providesDbObject() {
return new DbObject();
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
}
Component
package com.example.dagger2app;
import com.example.dagger2app.object.DbObject;
import com.example.dagger2app.object.HttpObject;
import dagger.Component;
//容器
@Component(modules = {HttpObject.class, DbObject.class})
public interface MyComponent {
void injectMainActivity(MainActivity activity);
}
Inject
package com.example.dagger2app;
import android.os.Bundle;
import android.util.Log;
import com.example.dagger2app.object.DbObject;
import com.example.dagger2app.object.HttpObject;
import javax.inject.Inject;
import androidx.appcompat.app.AppCompatActivity;
import dagger.Lazy;
public class MainActivity extends AppCompatActivity {
private final String TAG = this.getClass().getSimpleName();
@Inject
HttpObject httpObject;
@Inject
DbObject dbObject;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//方式一注解处理器帮忙new 所以注入的Module构造不能带参数
DaggerMyComponent.create().injectMainActivity(this);
//方式二适合构造传参 , 不建议使用，可以通过具体函数方法传参，create的最初目的是new对象
// DaggerMyComponent.builder()
// .httpObject(new HttpObject("www.google.com"))
// .dbObject(new DbObject())
// .build().injectMainActivity(this);
Log.e(TAG, "onCreate: " + httpObject.toString());
Log.e(TAG, "onCreate: " + httpObject.getUrl());
Log.e(TAG, "onCreate: " + dbObject.toString());
Log.e(TAG, "onCreate: " + dbObject.getName());
Log.e(TAG, "onCreate: " + dbObject.getAge());
}
}
@Singleton 局部单利
关于Singleton 单例，只需要在 Module 和 Component 添加相应的标注
@Module
public class HttpObject {
//省略....
@Singleton
@Provides
public HttpObject providesHttpObject() {
return new HttpObject();
}
}
@Singleton
@Component(modules = {HttpObject.class,DbObject.class})
public interface MyComponent {
void injectMainActivity(MainActivity activity);
}
@Singleton 全局单利
思考？为什么导致？在容器提供注册的时候有上下文活动Activity，导致对象不是同一个
如果是要做全局的单利，那么容器的创建放到 Android - MyApplication 做全局
package com.example.dagger2app;
import android.app.Application;
public class MyApplication extends Application {
private MyComponent myComponent;
@Override
public void onCreate() {
super.onCreate();
myComponent = DaggerMyComponent.create();
}
public MyComponent getMyComponent() {
return myComponent;
}
}
@dependencies 组合容器，让多个容器组合成一个容器
副容器的写法修改下，不进行注入上下文，返回当期容器，给主容器使用
Module
package com.example.dagger2app.object;
import dagger.Module;
import dagger.Provides;
@Module
public class FileObject {
@Provides
public FileObject providesFileObject(){
return new FileObject();
}
}
Component（副，可以有多个）
package com.example.dagger2app;
import com.example.dagger2app.object.FileObject;
import dagger.Component;
@Component(modules = {FileObject.class})
public interface My2Component {
//使用依赖关系
FileObject getMy2Component();
}
Component（主，唯一） @dependencies 组合容器
package com.example.dagger2app;
import com.example.dagger2app.object.DbObject;
import com.example.dagger2app.object.HttpObject;
import dagger.Component;
//容器 modules，dependencies 组合容器，
@Component(modules = {HttpObject.class, DbObject.class}, dependencies = {My2Component.class})
public interface MyComponent {
void injectMainActivity(MainActivity activity);
}
原理分析
DaggerMyComponent.create().injectMainActivity(this);
通过进入生成的源码查看：
// Generated by Dagger (https://dagger.dev).
package com.example.dagger2app;
import com.example.dagger2app.object.DbObject;
import com.example.dagger2app.object.DbObject_ProvidesDbObjectFactory;
import com.example.dagger2app.object.HttpObject;
import com.example.dagger2app.object.HttpObject_ProvidesHttpObjectFactory;
import dagger.internal.Preconditions;
@SuppressWarnings({
"unchecked",
"rawtypes"
})
//方法名：Dagger+容器名ClassName 并且实现了容器接口
public final class DaggerMyComponent implements MyComponent {
//Module成了新Class的成员变量
private final HttpObject httpObject;
private final DbObject dbObject;
private DaggerMyComponent(HttpObject httpObjectParam, DbObject dbObjectParam) {
this.httpObject = httpObjectParam;
this.dbObject = dbObjectParam;
}
//构建者模式
public static Builder builder() {
return new Builder();
}
//自动new
public static MyComponent create() {
return new Builder().build();
}
//依赖注册的活动上下文 ，又重新的生成xxx2的函数工厂
@Override
public void injectMainActivity(MainActivity activity) {
injectMainActivity2(activity);
}
/**
*工厂模式，Provides注册到活动页面，
*如果在单例模式下面，Lazy<> get 是双重检验机制
*/
private MainActivity injectMainActivity2(MainActivity instance) {
MainActivity_MembersInjector.injectHttpObject(instance, HttpObject_ProvidesHttpObjectFactory.providesHttpObject(httpObject));
MainActivity_MembersInjector.injectDbObject(instance, DbObject_ProvidesDbObjectFactory.providesDbObject(dbObject));
return instance;
}
public static final class Builder {
private HttpObject httpObject;
private DbObject dbObject;
private Builder() {
}
public Builder httpObject(HttpObject httpObject) {
this.httpObject = Preconditions.checkNotNull(httpObject);
return this;
}
public Builder dbObject(DbObject dbObject) {
this.dbObject = Preconditions.checkNotNull(dbObject);
return this;
}
public MyComponent build() {
if (httpObject == null) {
this.httpObject = new HttpObject();
}
if (dbObject == null) {
this.dbObject = new DbObject();
}
return new DaggerMyComponent(httpObject, dbObject);
}
}
}