Dagger2学习笔记之Qualifier

最新推荐文章于 2021-05-28 06:44:49 发布

阿福-jacob

最新推荐文章于 2021-05-28 06:44:49 发布

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CC 4.0 BY-SA版权

文章标签： android Dagger2 依赖注入

本文链接：https://blog.youkuaiyun.com/qq_33994844/article/details/54972510

本文介绍Dagger2中Qualifier的使用方法，通过实例演示如何解决依赖注入时对象相同但来源不同的问题。采用Qualifier注解区分不同来源的对象，确保正确注入。

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dagger2在使用中，会出现两个方法返回对象相同时的情况，那么如何区分呢。

由Dagger2学习笔记之dependencies更改的demo

public class Present {

    String ss = "呵呵哒";
    public Present(Context context) {
    }
    public Present(String name) {
        this.ss = name;
    }
}

@Module
public class AppModule {

    Context mContext;
    public AppModule(Context context) {
        this.mContext = context;
    }

    @Provides
    public Context provicesContext(){
        return mContext;
    }

    @Provides
    public String provicesString(){
        return "盲僧";
    }
}

@Component(modules = {AppModule.class})
public interface AppComponent {

    //暴露一个接口
    Context proContext();
    //暴露一个接口
    String proString();
}

@Module
public class ActivityModule {


    @Named("context")
    @Provides
    Present providesPresent(Context context){
        return new Present(context);
    }

    @Named("string")
    @Provides
    Present providesPresentName(String name){
        return new Present("女警");
    }
}

@Component(dependencies = {AppComponent.class},modules = {ActivityModule.class})
public interface ActivityComponent {

    void injectActivity(Main3Activity activity);
}

public class Main3Activity extends AppCompatActivity {

    @Named("context")
    @Inject
    Present mPresent;
    @Named("string")
    @Inject
    Present mPresent2;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main3);

        AppComponent appComponent = DaggerAppComponent.builder().appModule(new AppModule(this)).build();
        ActivityComponent activityComponent = DaggerActivityComponent.builder()
                .appComponent(appComponent)
                .activityModule(new ActivityModule())
                .build();

        activityComponent.injectActivity(this);
        Log.e("",mPresent.ss+"    "+mPresent2.ss);
    }
}

打印结果为:呵呵哒女警

注意点:

1:Main3Activity中的属性必须用@Named("xxx")进行标注

2:ActivityModule中也需要@Named("xxx")进行标注

可以看出来,我们在用@Named时,很容易把括号里面的内容填写错误,这时Qualifiler(限定符,自定义标记)的作用

创建两个注解

@Qualifier
@Retention(RetentionPolicy.RUNTIME)  // 运行时仍可用
public @interface PresentForContext {
}

@Qualifier
@Retention(RetentionPolicy.RUNTIME)  // 运行时仍可用
public @interface PresentForName {
}

再把上面demo中的@Named("xx")替换掉就行

@Module
public class ActivityModule {


    @PresentForContext
    @Provides
    Present providesPresent(Context context){
        return new Present(context);
    }

    @PresentForName
    @Provides
    Present providesPresentName(String name){
        return new Present(name);
    }
}

public class Main3Activity extends AppCompatActivity {

    @PresentForContext
    @Inject
    Present mPresent;
    @PresentForName
    @Inject
    Present mPresent2;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main3);

        AppComponent appComponent = DaggerAppComponent.builder().appModule(new AppModule(this)).build();
        ActivityComponent activityComponent = DaggerActivityComponent.builder()
                .appComponent(appComponent)
                .activityModule(new ActivityModule())
                .build();

        activityComponent.injectActivity(this);
        Log.e("",mPresent.ss+"    "+mPresent2.ss);
    }
}

这就是Qualifiter的用法