Dagger2子注入項為空

Question

使用dagger2的簡單示例

更新

我有一個馬達班，有計算機班和水泵班。 我之所以這樣寫它們，是因為為什么Motor中的子注入零件為空？

這是我的帶有startEngin方法的馬達類，該方法檢查計算機和waterPump以啟動。

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;
        }
    }

}

這是具有型號名稱和電壓的計算機類：

public class Computer {

    private int vultage;
    private String model;

    public Computer(String model ,int vultage){

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

這是WaterPump：

public class WaterPump {

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

這是我的模塊：

@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;
    }

}

這是我的組件類，我知道不需要getMotor方法。

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

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

在這里，在活動注入的電機中為空：

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

對我來說，一切看起來都不錯，除了賽車課本身。 您用@Inject注釋了兩個字段（因此Dagger現在知道它可以在其中注入內容），但是您從未真正要求Dagger用數據“填充”這些變量。 您應該明確地要求在代碼中的某處填充這些數據。 一種方法是通過“構造函數注入”，這就是構造函數的外觀

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

...並在模塊中：

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

或者，您可以從Motor的構造器調用dagger實例，然后執行以下操作：

myDaggerInstance.inject(this);

並記得使用@Inject注釋為Motor的構造函數進行注釋。

無論使用哪種方式，您都明確地告訴Dagger在某個時間點實現這些依賴關系，因此它們不再為null。 干杯!

Answer 2

您需要保存對MotorComponent實例的引用，並將其用於注入Activtiy和Motor類。 將void inject（Motor m）添加到您的組件中，然后調用component.inject（myMotor），或者改為對Motor類使用構造函數注入。

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(){
    }

應為以下之一：

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();
//}

要么

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);
}