Fatal编程技术网
  • java/
  • Java 在Dagger 2中的活动中传递应用程序上下文（NullPointerException）

Java 在Dagger 2中的活动中传递应用程序上下文（NullPointerException）

java android dependency-injection

Java 在Dagger 2中的活动中传递应用程序上下文（NullPointerException）,java,android,dependency-injection,dagger-2,dagger,Java,Android,Dependency Injection,Dagger 2,Dagger,我试图在Dagger 2中传递应用程序上下文活动。非常感谢您的任何帮助！！最后我提供了我的Logcat控制台 格雷戈里·基克（Gregory Kick）的项目给了我同样的问题，如最后一个错误部分所示 我还尝试基于此问题进行改进： 什么都没用！我知道活动中实际上不需要应用程序上下文，因为活动中有活动上下文。但我只是想知道如何在任何类（例如活动）中传递应用程序上下文 应用程序类（NannyApplication.java） MainActivity.java（这里，我想从NannyApplicati

我试图在Dagger 2中传递应用程序上下文活动。非常感谢您的任何帮助！！最后我提供了我的Logcat控制台

格雷戈里·基克（Gregory Kick）的项目给了我同样的问题，如最后一个错误部分所示

我还尝试基于此问题进行改进：

什么都没用！我知道活动中实际上不需要应用程序上下文，因为活动中有活动上下文。但我只是想知道如何在任何类（例如活动）中传递应用程序上下文

应用程序类（NannyApplication.java）

MainActivity.java（这里，我想从NannyApplication.java注入上下文）

匕首应用程序组件（NannyApplicationComponent.java）

错误，我得到了

03-27 19:08:37.107 10619-10619/com.nexuslab.forensics.grr.nanny E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.nexuslab.forensics.grr.nanny, PID: 10619
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.nexuslab.forensics.grr.nanny/com.nexuslab.forensics.grr.nanny.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String[] com.nexuslab.forensics.grr.nanny.NannyApplication.databaseList()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2946)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3046)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1688)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6809)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String[] com.nexuslab.forensics.grr.nanny.NannyApplication.databaseList()' on a null object reference
        at com.nexuslab.forensics.grr.nanny.MainActivity.onStart(MainActivity.java:26)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1412)
        at android.app.Activity.performStart(Activity.java:7015)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2909)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3046) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1688) 
        at android.os.Handler.dispatchMessage(Handler.java:105) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6809) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
我不能在下面的活动中使用任何类型的构造函数注入

 private NannyApplication nannyApplication;

    @Inject
    public MainActivity() {
        this.nannyApplication = nannyApplication;
    }
这就是为什么我使用现场注射：

@Inject NannyApplication nannyApplication; //Problem here
在应用程序类中进行如下更改

public class NannyApplication extends Application {
private DaggerNannyApplicationComponent daggerNannyApplicationComponent;

@Override
public void onCreate() {
    super.onCreate();
    daggerNannyApplicationComponent.builder().create().build();
}

public DaggerNannyApplicationComponent getComponent() {
    return daggerNannyApplicationComponent;
}
}这是一个有效的解决方案

规则：对于任何服务组件
T
，我们必须将T的实例作为
seedInstance
提供到
androidject.Builder
类中。这意味着如果在MainActivity的生命周期回调中执行
androidjector.inject（this）
，则在
androidjector.Builder
类中初始化了
seedInstance=MainActivity

这个
androidjector.Builder
，您将在
daggernanyapplicationcomponent的Builder
内部类中看到，因为在
nanyapplicationcomponent
中，您将编写

@Component.Builder /* Simply tells this Builder is DaggerNannyApplicationComponent’s inner Builder class */
    abstract class Builder extends AndroidInjector.Builder<NannyApplication> {
    }
NannyApplicationModule.java

package com.nexuslab.forensics.grr.nanny;

import android.app.Application;

import com.nexuslab.forensics.grr.nanny.di.component.DaggerNannyApplicationComponent;
/**
 * Created by gaute on 3/25/18.
 */

public class NannyApplication extends Application {

    @Override
    public void onCreate() {
        super.onCreate();
        DaggerNannyApplicationComponent.builder().create(this);
    }
}

package com.nexuslab.forensics.grr.nanny;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;

import javax.inject.Inject;

/**
 * @author gaute
 */
public class MainActivity extends AppCompatActivity {

    @Inject
    NannyApplication nannyApplication;

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

    @Override
    protected void onStart() {
        super.onStart();
        Utils.schedule(nannyApplication, HeartbeatService.class, Constants.HEARTBEAT_CHECK_INTERVAL);
        finishAndRemoveTask();
    }

}

package com.nexuslab.forensics.grr.nanny.di.component;


import com.nexuslab.forensics.grr.nanny.NannyApplication;
import com.nexuslab.forensics.grr.nanny.di.module.NannyApplicationModule;

import javax.inject.Singleton;

import dagger.Component;
import dagger.android.AndroidInjector;

/**
 * Created by gaute on 3/25/18.
 */

@Singleton
@Component(modules = NannyApplicationModule.class)
public interface NannyApplicationComponent extends AndroidInjector<NannyApplication> {

    @Component.Builder
    abstract class Builder extends AndroidInjector.Builder<NannyApplication> {
    }
}

package com.nexuslab.forensics.grr.nanny.di.module;

import com.nexuslab.forensics.grr.nanny.NannyApplication;

import javax.inject.Singleton;

import dagger.Module;
import dagger.Provides;
import dagger.android.AndroidInjectionModule;

@Module(includes = AndroidInjectionModule.class)
public class NannyApplicationModule {

    @Provides
    @Singleton
    NannyApplication getNannyApplication(NannyApplication nannyApplication) {
        return nannyApplication;
    }

}

@Singleton
@Component(modules = {
        AndroidSupportInjectionModule.class /* it makes Dagger generates DaggerNannyApplicationComponent */,
        ApplicationBindingModule.class /* it generats AndroidInjector.Builder<MainActivity>, which
        is used to inject requested dependencies by MainActivity */
})
public interface NannyApplicationComponent extends AndroidInjector<NannyApplication> {

    @Component.Builder /* Simply tells this Builder is DaggerNannyApplicationComponent’s inner Builder class */
    abstract class Builder extends AndroidInjector.Builder<NannyApplication> {
    }
}

 @Module
    public interface ApplicationBindingModule {

/* These two lines, actually, makes Dagger generates ApplicationBindingModule_MainActivity class */
        @ContributesAndroidInjector
        MainActivity mainActivity();
    }

@Module
public class NannyApplicationModule {
}

//MainActivity is a consumer because it has requested nannyApplication using @Inject annotation
public class MainActivity extends DaggerAppCompatActivity {

    @Inject
    NannyApplication nannyApplication /* You got the ApplicationContext */;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // AndroidInjection.inject(this); 
/* if Consumers want MainActivity instance then uncomment AndroidInjection.inject(this) line. Doing this makes MainActivity Consumer as well as Service component. Because it consumed nannyApplication but it has also provided (serviced) it's instance to the external world */
    }

    @Override
    protected void onStart() {
        super.onStart();
        //check nannyApplication
        Log.i("Cls-loader: ", nannyApplication.getClassLoader() + "");
    }
}

public class NannyApplication extends DaggerApplication {

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

    /**
     * applicationInjector() gets called inside onCreate()
     */
    @Override
    protected AndroidInjector<? extends DaggerApplication> applicationInjector() {
        return DaggerNannyApplicationComponent
                .builder()
                .create(this);
    }
}
MainActivity.java

package com.nexuslab.forensics.grr.nanny;

import android.app.Application;

import com.nexuslab.forensics.grr.nanny.di.component.DaggerNannyApplicationComponent;
/**
 * Created by gaute on 3/25/18.
 */

public class NannyApplication extends Application {

    @Override
    public void onCreate() {
        super.onCreate();
        DaggerNannyApplicationComponent.builder().create(this);
    }
}

package com.nexuslab.forensics.grr.nanny;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;

import javax.inject.Inject;

/**
 * @author gaute
 */
public class MainActivity extends AppCompatActivity {

    @Inject
    NannyApplication nannyApplication;

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

    @Override
    protected void onStart() {
        super.onStart();
        Utils.schedule(nannyApplication, HeartbeatService.class, Constants.HEARTBEAT_CHECK_INTERVAL);
        finishAndRemoveTask();
    }

}

package com.nexuslab.forensics.grr.nanny.di.component;


import com.nexuslab.forensics.grr.nanny.NannyApplication;
import com.nexuslab.forensics.grr.nanny.di.module.NannyApplicationModule;

import javax.inject.Singleton;

import dagger.Component;
import dagger.android.AndroidInjector;

/**
 * Created by gaute on 3/25/18.
 */

@Singleton
@Component(modules = NannyApplicationModule.class)
public interface NannyApplicationComponent extends AndroidInjector<NannyApplication> {

    @Component.Builder
    abstract class Builder extends AndroidInjector.Builder<NannyApplication> {
    }
}

package com.nexuslab.forensics.grr.nanny.di.module;

import com.nexuslab.forensics.grr.nanny.NannyApplication;

import javax.inject.Singleton;

import dagger.Module;
import dagger.Provides;
import dagger.android.AndroidInjectionModule;

@Module(includes = AndroidInjectionModule.class)
public class NannyApplicationModule {

    @Provides
    @Singleton
    NannyApplication getNannyApplication(NannyApplication nannyApplication) {
        return nannyApplication;
    }

}

@Singleton
@Component(modules = {
        AndroidSupportInjectionModule.class /* it makes Dagger generates DaggerNannyApplicationComponent */,
        ApplicationBindingModule.class /* it generats AndroidInjector.Builder<MainActivity>, which
        is used to inject requested dependencies by MainActivity */
})
public interface NannyApplicationComponent extends AndroidInjector<NannyApplication> {

    @Component.Builder /* Simply tells this Builder is DaggerNannyApplicationComponent’s inner Builder class */
    abstract class Builder extends AndroidInjector.Builder<NannyApplication> {
    }
}

 @Module
    public interface ApplicationBindingModule {

/* These two lines, actually, makes Dagger generates ApplicationBindingModule_MainActivity class */
        @ContributesAndroidInjector
        MainActivity mainActivity();
    }

@Module
public class NannyApplicationModule {
}

//MainActivity is a consumer because it has requested nannyApplication using @Inject annotation
public class MainActivity extends DaggerAppCompatActivity {

    @Inject
    NannyApplication nannyApplication /* You got the ApplicationContext */;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // AndroidInjection.inject(this); 
/* if Consumers want MainActivity instance then uncomment AndroidInjection.inject(this) line. Doing this makes MainActivity Consumer as well as Service component. Because it consumed nannyApplication but it has also provided (serviced) it's instance to the external world */
    }

    @Override
    protected void onStart() {
        super.onStart();
        //check nannyApplication
        Log.i("Cls-loader: ", nannyApplication.getClassLoader() + "");
    }
}

public class NannyApplication extends DaggerApplication {

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

    /**
     * applicationInjector() gets called inside onCreate()
     */
    @Override
    protected AndroidInjector<? extends DaggerApplication> applicationInjector() {
        return DaggerNannyApplicationComponent
                .builder()
                .create(this);
    }
}
NannyApplication.java

package com.nexuslab.forensics.grr.nanny;

import android.app.Application;

import com.nexuslab.forensics.grr.nanny.di.component.DaggerNannyApplicationComponent;
/**
 * Created by gaute on 3/25/18.
 */

public class NannyApplication extends Application {

    @Override
    public void onCreate() {
        super.onCreate();
        DaggerNannyApplicationComponent.builder().create(this);
    }
}

package com.nexuslab.forensics.grr.nanny;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;

import javax.inject.Inject;

/**
 * @author gaute
 */
public class MainActivity extends AppCompatActivity {

    @Inject
    NannyApplication nannyApplication;

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

    @Override
    protected void onStart() {
        super.onStart();
        Utils.schedule(nannyApplication, HeartbeatService.class, Constants.HEARTBEAT_CHECK_INTERVAL);
        finishAndRemoveTask();
    }

}

package com.nexuslab.forensics.grr.nanny.di.component;


import com.nexuslab.forensics.grr.nanny.NannyApplication;
import com.nexuslab.forensics.grr.nanny.di.module.NannyApplicationModule;

import javax.inject.Singleton;

import dagger.Component;
import dagger.android.AndroidInjector;

/**
 * Created by gaute on 3/25/18.
 */

@Singleton
@Component(modules = NannyApplicationModule.class)
public interface NannyApplicationComponent extends AndroidInjector<NannyApplication> {

    @Component.Builder
    abstract class Builder extends AndroidInjector.Builder<NannyApplication> {
    }
}

package com.nexuslab.forensics.grr.nanny.di.module;

import com.nexuslab.forensics.grr.nanny.NannyApplication;

import javax.inject.Singleton;

import dagger.Module;
import dagger.Provides;
import dagger.android.AndroidInjectionModule;

@Module(includes = AndroidInjectionModule.class)
public class NannyApplicationModule {

    @Provides
    @Singleton
    NannyApplication getNannyApplication(NannyApplication nannyApplication) {
        return nannyApplication;
    }

}

@Singleton
@Component(modules = {
        AndroidSupportInjectionModule.class /* it makes Dagger generates DaggerNannyApplicationComponent */,
        ApplicationBindingModule.class /* it generats AndroidInjector.Builder<MainActivity>, which
        is used to inject requested dependencies by MainActivity */
})
public interface NannyApplicationComponent extends AndroidInjector<NannyApplication> {

    @Component.Builder /* Simply tells this Builder is DaggerNannyApplicationComponent’s inner Builder class */
    abstract class Builder extends AndroidInjector.Builder<NannyApplication> {
    }
}

 @Module
    public interface ApplicationBindingModule {

/* These two lines, actually, makes Dagger generates ApplicationBindingModule_MainActivity class */
        @ContributesAndroidInjector
        MainActivity mainActivity();
    }

@Module
public class NannyApplicationModule {
}

//MainActivity is a consumer because it has requested nannyApplication using @Inject annotation
public class MainActivity extends DaggerAppCompatActivity {

    @Inject
    NannyApplication nannyApplication /* You got the ApplicationContext */;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // AndroidInjection.inject(this); 
/* if Consumers want MainActivity instance then uncomment AndroidInjection.inject(this) line. Doing this makes MainActivity Consumer as well as Service component. Because it consumed nannyApplication but it has also provided (serviced) it's instance to the external world */
    }

    @Override
    protected void onStart() {
        super.onStart();
        //check nannyApplication
        Log.i("Cls-loader: ", nannyApplication.getClassLoader() + "");
    }
}

public class NannyApplication extends DaggerApplication {

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

    /**
     * applicationInjector() gets called inside onCreate()
     */
    @Override
    protected AndroidInjector<? extends DaggerApplication> applicationInjector() {
        return DaggerNannyApplicationComponent
                .builder()
                .create(this);
    }
}

公共类NannyaApplication扩展了DaggerApplication{
@凌驾
public void onCreate（）{
super.onCreate（）；
}
/**
*applicationInjector（）在onCreate（）内被调用
*/
@凌驾

受保护的AndroidObject
daggerNannyApplicationComponent.builder（）.create（）.build（）；
不正确，因为
builder（）
是一个静态方法。其次，为什么需要
getComponent（）
方法，因为我没有在任何地方使用
daggerNannyApplicationComponent
。如果您愿意，我将使用dagger 2为room数据库提供一个演示。我看到一个空的
onCreate
并且没有调用
activityComponent.inject（activity）
。您将在哪里注入活动？
@Inject
不会注入任何没有获取called@DavidMedenjak，谢谢！对我来说，要理解Dagger 2生成的框架有点困难。我解决了这个问题。我将发布更新的答案，并提供每一点详细的解释，以便它真的有帮助我刚刚为这个问题创建了一个示例项目，以便帮助其他正在等待我答案的用户。