Question

使用dagger2的简单示例

已更新

我有一个拥有Computer和waterpump类的Motor类。我这样写的是为什么Motor中的子注入部件为空？

这是我的运动类，使用startEngin方法检查计算机和waterPump启动。

public class Motor {

    @Inject
    public Computer computer;

    @Inject
    public WaterPump waterPump;


    public Motor(){
    }

// here computer and waterPump are null and not injected
    public boolean startEngin(){
        if(computer!=null && waterPump!=null){
            return true;
        }else{
            return false;
        }
    }

}

这是具有型号名称和电压的计算机类：

public class Computer {

    private int vultage;
    private String model;

    public Computer(String model ,int vultage){

        this.model=model;
        this.vultage = vultage;
    }
}

这是WaterPump：

public class WaterPump {

    private String name;
    public WaterPump(String name){
        this.name = name;
    }
}

这是我的模块：

@Module
public class MotorModule {

    Context context;
    String motoName;
    String computerName;
    String waterPupName;
    int voltage;

    public MotorModule(Context context, String computerName, String waterPupName, int voltage) {
        this.context = context;
        this.waterPupName = waterPupName;
        this.computerName = computerName;
        this.voltage = voltage;
    }

    @Provides
    @Singleton
    Motor provideMotor() {
        return new Motor();
    }

    @Provides
    @Singleton
    Computer provideComputer() {
        return new Computer(computerName, voltage);
    }

    @Provides
    @Singleton
    WaterPump provideWaterPump() {
        return new WaterPump(waterPupName);
    }

    @Provides
    @Singleton
    Context provideContext() {
        return this.context;
    }

}

这是我的组件类，我知道不需要getMotor方法。

@Singleton
@Component(modules = {MotorModule.class})
public interface MotorComponent {

//    Motor getMotor();
    void inject(MainActivity activty);

并且在活动中注入的电机为空：

public class MainActivity extends AppCompatActivity {

    @Inject
    public Motor motor;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        DaggerMotorComponent.builder().motorModule(new MotorModule
                (this, "mahdi'PC", "my " +
                        "Water pump", 12)).build().inject(this);

        if (motor.startEngin()) {

            Toast.makeText(this, "it is started", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(this, "motor is not provided", Toast.LENGTH_SHORT).show();
        }

    }

}

}

Answer 1

一切看起来都不错，除了Motor类本身。你用@Inject注释了两个字段（所以Dagger现在知道它可以在那里注入东西），但你实际上从未要求Dagger用数据“填充”这些变量。您应该明确要求在代码中的某处填写这些数据。 1种方法是通过'构造函数注入'，这样你的构造函数应该是什么样的

public Motor(Computer computer, WaterPump waterPump) {
this.computer = computer;
this.waterPump = waterPump;
}

......并在模块中：

@Provides
@Singleton
Motor provideMotor(Computer computer, Waterpump waterpump) {
    return new Motor(computer, waterpump);
}

或者你可以从你的Motor的构造函数中调用dagger实例并执行以下操作：

myDaggerInstance.inject(this);

并记得使用@Inject注释为Motor注释构造函数。

使用任何一种方法，你明确告诉Dagger在某个时间点完成这些依赖，所以它们不再是null。干杯！

Answer 2

您需要保存对MotorComponent实例的引用，并使用它注入Activtiy和Motor类。将void inject（Motor m）添加到组件中，并调用component.inject（myMotor），或者在Motor类上使用构造函数注入。

public class Motor {

    Computer computer;
    WaterPump waterPump;


    public Motor( Computer computer, WaterPump waterPump){
        this.computer = computer;
        this.waterPump = waterPump;
    }

    // here computer and waterPump are null and not injected
    public boolean startEngin(){
        if(computer!=null && waterPump!=null){
            return true;
        }else{
            return false;
        }
    }

}

/** Add method, providing Motor class instance - it will use another
 .provide() methods from this component to get computer and waterpump objects
 (Costtructor injection)
 */

    /**
     * Arguments is provided by DI
     * @param computer
     * @param waterPump
     * @return
     */
    @Provides
@Singleton
Motor provideMotors(Computer computer, WaterPump waterPump) {
    Motor motor = new Motor(computer, waterPump);
        return motor
}

/** Store reference to your component (better do it in Application) */

MotorComponent component = DaggerMotorComponent.builder().motorModule(new MotorModule
        (this, "mahdi'PC", "my " +
                "Water pump", 12)).build();

// inject into Activity
componen.inhject(this);

Answer 3

@Provides
@Singleton
Motor provideMotor() {
    return new Motor();
}

和

public class Motor {

    @Inject
    public Computer computer;

    @Inject
    public WaterPump waterPump;


    public Motor(){
    }

应该是以下之一：

1）

@Singleton
public class Motor {
    @Inject
    public Computer computer;

    @Inject
    public WaterPump waterPump;

    @Inject
    public Motor() {
    }

和

public MotorModule(Context context, String computerName, String waterPupName, int voltage) {
    this.context = context;
    this.waterPupName = waterPupName;
    this.computerName = computerName;
    this.voltage = voltage;
}

//@Provides
//@Singleton
//Motor provideMotor() {
//    return new Motor();
//}

或

2）。

public class Motor { public Computer computer; public WaterPump waterPump; public Motor(Computer computer, WaterPump waterPump) { this.computer = computer; this.waterPump = waterPump; }

和

@Provides @Singleton Motor provideMotor(Computer computer, WaterPump waterPump) { return new Motor(computer, waterPump); }

Dagger2子注入项为空

3 个答案: