Dagger2基本用法及标签详解

Dagger2是一个基于JSR-330标准的依赖注入框架，在编译期间自动生成代码，负责依赖对象的创建。为了进一步解耦和方便测试，我们会使用依赖注入的方式构建对象。

Demo下载

使用：

compile 'com.google.dagger:dagger:2.4'
annotationProcessor 'com.google.dagger:dagger-compiler:2.4'

一、@Inject 和@component

看图：

public class TestInject {

    @Inject
    public TestInject(){}

    public String getStr(){
        return "Test Inject and Component";
    }

}

@Component
public interface TestActivityComponent {
    void inject(TestActivity testActivity);
}

public class TestActivity extends AppCompatActivity {

    @Inject
    TestInject testInject;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        DaggerTestActivityComponent.create().inject(this);
        ((TextView)findViewById(R.id.tv)).setText(testInject.getStr());
    }
}

二、@module 和 @prodives

无法在第三方库的构造器上加上@Inject注解，可以通过这两个注解

public interface ITest {
    String getStr();
}

public class Test1 implements ITest {
    @Override
    public String getStr() {
        return "test1";
    }
}

@Module
public class TestModule {

    @Provides
    ITest getProvide(){
        return new Test1();
    }

}

@Component(modules = TestModule.class)
public interface TestActivityComponent {
    void inject(TestActivity testActivity);
}

public class TestActivity extends AppCompatActivity {

    @Inject
    ITest testInject;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        DaggerTestActivityComponent.create().inject(this);
        ((TextView)findViewById(R.id.tv)).setText(testInject.getStr());
    }
}

三、@Name

继承同一父类时，通过该标签指定需要实例化的子类

public interface Test {
    String getStr();
}

public class Test1 implements Test {
    @Override
    public String getStr() {
        return "test1";
    }
}

public class Test2 implements Test {
    @Override
    public String getStr() {
        return "test2";
    }
}

@Module
public class TestModule {

    @Provides
    @Named("Test1")
    Test1 provideTest1(){
        return new Test1();
    }

    @Provides
    @Named("Test2")
    Test2 provideTest2(){
        return new Test2();
    }

}

@Component(modules = TestModule.class)
public interface TestActivityComponent {
    void inject(TestActivity testActivity);
}

public class TestActivity extends AppCompatActivity {

    Test1 testInject1;
    Test2 testInject2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        DaggerTestActivityComponent.create().inject(this);
        ((TextView)findViewById(R.id.tv)).setText(testInject2.getStr());
    }

    @Inject
    public void getTestInject1(@Named("Test1") Test1 test1) {
        testInject1=test1;
    }

    @Inject
    public void getTestInject2(@Named("Test2") Test2 test2) {
        testInject2=test2;
    }
}

四、@qualifier

和@Name作用相同，用法不同而已

@Qualifier
@Retention(RetentionPolicy.RUNTIME)
public @interface Test1 {
}

@Qualifier
@Retention(RetentionPolicy.RUNTIME)
public @interface Test2 {
}

public interface Test {

    String getStr();

}

public class Test1 implements Test {
    @Override
    public String getStr() {
        return "test1";
    }
}

public class Test2 implements Test {
    @Override
    public String getStr() {
        return "test2";
    }
}

@Module
public class TestModule {

    @Provides
    @com.example.pateo.myapplication.qualifier.annotation.Test1
    Test1 provideTest1(){
        return new Test1();
    }

    @Provides
    @com.example.pateo.myapplication.qualifier.annotation.Test2
    Test2 provideTest2(){
        return new Test2();
    }

}

@Component(modules = TestModule.class)
public interface TestActivityComponent {
    void inject(TestActivity testActivity);
}

public class TestActivity extends AppCompatActivity {

    Test1 testInject1;
    Test2 testInject2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        DaggerTestActivityComponent.create().inject(this);
        ((TextView)findViewById(R.id.tv)).setText(testInject1.getStr());
    }

    @Inject
    public void getTestInject1(@com.example.pateo.myapplication.qualifier.annotation.Test1 Test1 test1) {
        testInject1=test1;
    }

    @Inject
    public void getTestInject2(@com.example.pateo.myapplication.qualifier.annotation.Test2 Test2 test2) {
        testInject2=test2;
    }
}

五、@lazy 

懒加载标签，使用时通过get方法加载

public class TestInject {

    @Inject
    public TestInject(){}

    public String getStr(){
        return "Test Lazy";
    }

}

@Component
public interface TestActivityComponent {
    void inject(TestActivity testActivity);
}

public class TestActivity extends AppCompatActivity {

    @Inject
    Lazy<TestInject> testInjects;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        DaggerTestActivityComponent.create().inject(this);
        ((TextView)findViewById(R.id.tv)).setText(testInjects.get().getStr());
    }
}