JetPack——Hilt - 技术栈

手动依赖注入

LoginRetrofitService

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public class LoginRetrofitService {
}

UserRemoteDataSource

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public class UserRemoteDataSource {

    private final LoginRetrofitService loginService;

    public UserRemoteDataSource(LoginRetrofitService loginService) {
        this.loginService = loginService;
    }
}

UserLocalDataSource

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public class UserLocalDataSource {
}

UserRepository

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public class UserRepository {

    private final UserLocalDataSource localDataSource;
    private final UserRemoteDataSource remoteDataSource;

    public UserRepository(UserLocalDataSource localDataSource,
                          UserRemoteDataSource remoteDataSource) {
        this.localDataSource = localDataSource;
        this.remoteDataSource = remoteDataSource;
    }
}

LoginViewModelFactory

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public class LoginViewModelFactory implements ViewModelProvider.Factory {

    private final UserRepository userRepository;

    public LoginViewModelFactory(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    @NonNull
    @Override
    @SuppressWarnings("unchecked")
    public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
        return (T) new LoginViewModel(userRepository);
    }
}

LoginViewModel

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public class LoginViewModel extends ViewModel {

    private final UserRepository userRepository;

    public LoginViewModel(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
}

ManualLoginActivity

想要获取LoginViewModel，需要根据依赖关系依次创建LoginRetrofitService、UserLocalDataSource、UserRemoteDataSource、UserRepository、LoginViewModelFactory

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public class ManualLoginActivity extends AppCompatActivity {

    private static final String TAG = ManualLoginActivity.class.getSimpleName();

    private LoginViewModel loginViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        LoginRetrofitService loginService = new LoginRetrofitService();
        UserLocalDataSource localDataSource = new UserLocalDataSource();
        UserRemoteDataSource remoteDataSource = new UserRemoteDataSource(loginService);
        UserRepository userRepository = new UserRepository(localDataSource, remoteDataSource);
        LoginViewModelFactory factory = new LoginViewModelFactory(userRepository);
        loginViewModel = new ViewModelProvider(this, factory).get(LoginViewModel.class);

        String msg = "【手动DI】依赖注入成功,ViewModel = " + loginViewModel;
        Log.d(TAG, msg);
        showText(msg);
    }

    private void showText(String text) {
        TextView tv = new TextView(this);
        tv.setText(text);
        tv.setGravity(Gravity.CENTER);
        tv.setTextColor(Color.BLACK);
        tv.setPadding(32, 200, 32, 32);
        setContentView(tv);
    }
}

Hilt

实现依赖项注入可为您带来以下优势：

重用代码
易于重构
易于测试

Hilt 是 Android 的依赖项注入库，可减少在项目中执行手动依赖项注入的样板代码

依赖

libs.version.toml

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[versions]
......
ksp = "2.0.20-1.0.24"
hilt = "2.57.1"

[libraries]
......
hilt-android = { group = "com.google.dagger", name = "hilt-android", version.ref = "hilt" }
hilt-compiler = { group = "com.google.dagger", name = "hilt-compiler", version.ref = "hilt" }

[plugins]
......
ksp = { id = "com.google.devtools.ksp", version.ref = "ksp" }
hilt = { id = "com.google.dagger.hilt.android", version.ref = "hilt" }

build.gradle（根目录）

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plugins {
    ......
    alias(libs.plugins.ksp) apply false
    alias(libs.plugins.hilt) apply false
}

build.gradle（项目目录）

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android {
	......
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_17
        targetCompatibility JavaVersion.VERSION_17
    }
    kotlinOptions {
        jvmTarget = '17'
    }
}
plugins {
	......
    alias(libs.plugins.ksp)
    alias(libs.plugins.hilt)
}
dependencies {
	......
    implementation libs.hilt.android
    ksp libs.hilt.compiler
}

Hilt 依赖注入

MyApplication

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@HiltAndroidApp
public class MyApplication extends Application {

    private static MyApplication instance;

    @Override
    public void onCreate() {
        super.onCreate();
        instance = this;
    }

    public static Context getContext() {
        return instance;
    }

}

LoginRetrofitService

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public class LoginRetrofitService {

    @Inject
    public LoginRetrofitService() {
    }
}

UserRemoteDataSource

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public class UserRemoteDataSource {

    private final LoginRetrofitService loginService;

    @Inject
    public UserRemoteDataSource(LoginRetrofitService loginService) {
        this.loginService = loginService;
    }
}

UserLocalDataSource

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public class UserLocalDataSource {

    @Inject
    public UserLocalDataSource() {
    }
}

UserRepository

@Singleton 全 App 共享一个

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@Singleton
public class UserRepository {

    private final UserLocalDataSource localDataSource;
    private final UserRemoteDataSource remoteDataSource;

    @Inject
    public UserRepository(UserLocalDataSource localDataSource,
                          UserRemoteDataSource remoteDataSource) {
        this.localDataSource = localDataSource;
        this.remoteDataSource = remoteDataSource;
    }
}

LoginViewModel

@HiltViewModel + 构造函数 @Inject → 依赖自动装配,不再需要手写 Factory。

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@HiltViewModel
public class LoginViewModel extends ViewModel {

    private final UserRepository userRepository;

    @Inject
    public LoginViewModel(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
}

HiltLoginActivity

为带有 @AndroidEntryPoint 注解的其他 Android 类提供依赖项，省去new的过程

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@AndroidEntryPoint
public class HiltLoginActivity extends AppCompatActivity {

    private static final String TAG = HiltLoginActivity.class.getSimpleName();

    private LoginViewModel loginViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // 一行搞定:Hilt 已经把 UserRepository 及其下层依赖全部装配好
        loginViewModel = new ViewModelProvider(this).get(LoginViewModel.class);

        String msg = "【Hilt】依赖注入成功,ViewModel = " + loginViewModel;
        Log.d(TAG, msg);
        showText(msg);
    }

    private void showText(String text) {
        TextView tv = new TextView(this);
        tv.setText(text);
        tv.setGravity(Gravity.CENTER);
        tv.setTextColor(Color.BLACK);
        tv.setPadding(32, 200, 32, 32);
        setContentView(tv);
    }
}

@Module和@InstallIn

@Module 注解的类向 Hilt 提供有关如何创建无法通过构造函数注入提供的类型（例如接口或第三方类）的实例
@InstallIn 告知 Hilt 每个模块将用在或安装在哪个 Android 类中

@Bind 注入接口

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public interface DemoInterface {
    String demo();
}

public class DemoImpl implements DemoInterface {

    @Inject
    public DemoImpl() {
    }

    @Override
    public String demo() {
        return "DemoImpl";
    }
}

存在接口和具体实现，创建一个带有 @Binds 注解的抽象函数实现接口的依赖注入

返回值为接口

参数为实现

@Module
@InstallIn(SingletonComponent.class)
public abstract class DemoModule {
@Binds
public abstract DemoInterface bind(DemoImpl impl);
}

@AndroidEntryPoint
public class HiltModuleActivity extends AppCompatActivity {

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  private static final String TAG = HiltModuleActivity.class.getSimpleName();
  @Inject
  DemoInterface mDemo;   // 业务用接口

  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);

      LinearLayout root = new LinearLayout(this);
      root.setOrientation(LinearLayout.VERTICAL);
      root.setPadding(48, 200, 48, 48);

      TextView tv = new TextView(this);
      tv.setGravity(Gravity.CENTER);
      tv.setTextColor(Color.BLACK);
      root.addView(tv);

      setContentView(root);

      String msg = "当前实现:" + mDemo.demo();
      Log.d(TAG, msg);
      tv.setText(msg);
  }

}

@Provides 注入外部库

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@Module
@InstallIn(SingletonComponent.class)
public class DemoModule {

    @Provides
    public Gson provideGson() {
        return new GsonBuilder().create();
    }
}

@AndroidEntryPoint
public class HiltModuleActivity extends AppCompatActivity {

    @Inject
    Gson gson;   // @Provides 提供的实例

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        TextView tv = new TextView(this);
        tv.setText("Gson实例:" + gson.toJson("hello @Provides"));
        setContentView(tv);
    }
}

@Qualifier和@Retention

@Qualifier 为同一类型定义多个绑定
@Retention 设置注解声明周期

如下生成@PrettyGson注解，用于Gson实例对象的依赖注入

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@Qualifier
@Retention(RetentionPolicy.RUNTIME)
public @interface PrettyGson {
}

@Module
@InstallIn(SingletonComponent.class)
public class DemoModule {

    // 默认绑定:压缩输出。
    @Provides
    public Gson provideGson() {
        return new GsonBuilder().create();
    }

    // 同类型的第二个绑定,靠 @PrettyGson 限定符区分,避免和上面的冲突。
    @Provides
    @PrettyGson
    public Gson providePrettyGson() {
        return new GsonBuilder().setPrettyPrinting().create();
    }
}

@AndroidEntryPoint
public class HiltModuleActivity extends AppCompatActivity {

    @Inject
    Gson gson;            // 默认绑定

    @Inject
    @PrettyGson
    Gson prettyGson;      // 限定符绑定

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // 用带字段的对象序列化,才能看出 setPrettyPrinting() 的换行缩进效果;
        // 序列化单个字符串没有"结构",两种输出会一样。
        Map<String, String> data = new HashMap<>();
        data.put("name", "Kiro");
        data.put("action", "@Provides demo");

        String compact = gson.toJson(data);
        String pretty = prettyGson.toJson(data);

        TextView tv = new TextView(this);
        tv.setText("默认Gson: " + compact
                + "\n\nPrettyGson:\n" + pretty);
        setContentView(tv);
    }
}

自带的预定义限定符

如下注入ApplicationContext和ActivityContext

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@Inject
@ApplicationContext
Context appContext;

@Inject
@ActivityContext
Context activityContext;