Android 依赖注入框架RoboGuice

劳灵均

2023-12-01

概述

在开发应用时一个基本原则是模块化，并且尽最大可能性地降低模块之间的耦合性。Dependency injection 大大降低了类之间的依赖性，可以通过annotation描述类之间的依赖性，避免了直接调用类似的构造函数或是使用Factory来参加所需的类，从而降低类或模块之间的耦合性，以提高代码重用并增强代码的可维护性。

Google Guice提供了Java平台上一个轻量级的 Dependency injection 框架，并可以支持开发Android应用。本指南将使用Android平台来说明Google Guice的用法。(其他类似框架有Dagger,Buffernife)

RoboGuice 为Android平台上基于Google Guice开发的一个库，可以大大简化Android应用开发的代码和一些繁琐重复的代码。比如代码中可能需要大量使用findViewById在XML中查找一个View，并将其强制转换到所需类型，onCreate 中可能有大量的类似代码。RoboGuice 允许使用annotation 的方式来描述id于View之间的关系，其余的工作由roboGuice库来完成。

RoboGuice主要功能：

控件注入：用@InjectViews方法初始化控件，例如：@InjectView（R.id.textview1）TextView textView1。
资源注入：用@InjectResources方法初始化资源，例如：@InjectResource（R.string.app_name）String name。
系统服务注入：用@Inject方法初始化并获取系统服务，例如：@Inject LayoutInflater inflater。
POJO对象注入：用@Inject方法注入并初始化POJO对象，例如：@Inject Foo foo。

以下示例对比看看RoboGuice的作用：

不使用RoboGuice:

    public void onCreate(Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState); 
            setContentView(R.layout.main);
            name      = (TextView) findViewById(R.id.name); 
            thumbnail = (ImageView) findViewById(R.id.thumbnail); 
            loc       = (LocationManager) getSystemService(Activity.LOCATION_SERVICE); 
            icon      = getResources().getDrawable(R.drawable.icon); 
            myName    = getString(R.string.app_name); 
            name.setText( "Hello, " + myName ); 
        } 
    }

使用RoboGuice:

 @ContentView(R.layout.main)
    class RoboWay extends RoboActivity { 
        @InjectView(R.id.name)             TextView name; 
        @InjectView(R.id.thumbnail)        ImageView thumbnail; 
        @InjectResource(R.drawable.icon)   Drawable icon; 
        @InjectResource(R.string.app_name) String myName; 
        @Inject                            LocationManager loc; 

        public void onCreate(Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState); 
            name.setText( "Hello, " + myName ); 
        } 
    }

使用前准备工作

RoboGuice官方Demo: https://github.com/roboguice/roboguice/tree/master/astroboy

安装

方式一：添加依赖库：（不推荐，在androidStudio上报错，很诡异。不知道为什么）

RoboGuice 3.0
RoboBlender 3.0
jsr330 javax.inject (JSR-330 support)
jsr305 (optional support for @Nullable annotation, if desired)

方式二：在build.gradle中的dependecies片段中添加：(推荐)

dependencies {
    provided 'org.roboguice:roboblender:3.0'
    compile 'org.roboguice:roboguice:3.0'
}

参考https://github.com/roboguice/roboguice/wiki/InstallationNonMaven

继承类：

activities, services, and fragments都需要继承自RoboGuice提供的下列类：

RoboActivity
RoboListActivity
RoboExpandableListActivity
RoboMapActivity
RoboPreferenceActivity
RoboAccountAuthenticatorActivity
RoboActivityGroup
RoboTabActivity
RoboFragmentActivity
RoboLauncherActivity
RoboService
RoboIntentService
RoboFragment
RoboListFragment
RoboDialogFragment
etc.

Injection

Inherit from RoboActivity
Set your content view
Annotate your views with @InjectView

public class MyActivity extends RoboActivity {
        @InjectView(R.id.text1) TextView textView;

        @Override
        protected void onCreate( Bundle savedState ) {
            setContentView(R.layout.myactivity_layout);
            textView.setText("Hello!");
        }
    }

@ContentView注解：

  @ContentView(R.layout.myactivity_layout)
    public class MyActivity extends RoboActivity {
        @InjectView(R.id.text1) TextView textView;

        @Override
        protected void onCreate( Bundle savedState ) {
            textView.setText("Hello!");
        }
    }

将View注入Fragment@InjectView

由于Fragment中的依赖注入发生在onViewCreated()中，所以需要在onViewCreated中调用super.onViewCreate()之后才能使用注入的View.

注意这里的：onViewCreated是在onCreateView调用之后恢复保存的状态到View之前立马调用，

@InjectView TextView commentEditText;

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    commentEditText.setText("Some comment");
}

注入Resource到Activity:@InjectResource

public class MyActivity extends RoboActivity {
    @InjectResource(R.anim.my_animation) Animation myAnimation;
}

注入System Service:@Inject

class MyActivity extends RoboActivity {
    @Inject Vibrator vibrator;
    @Inject NotificationManager notificationManager;

注入POJO:@Inject

注意：需要提供一个无参数构造器

class MyActivity extends RoboActivity {
    @Inject Foo foo; // this will basically call new Foo();
}

当然如果不想使用默认构造器，可以注解构造器：

class Foo {
    Bar bar;
    @Inject
    public Foo(Bar bar) {
        this.bar = bar;
    }
}

也可以注解POJO的Field:

class Foo {
    @Inject Bar bar;

    // Roboguice doesn't need a constructor, but you might...
}

注入Singleton

前提：对单例类使用@Singleton

@Singleton //a single instance of Foo is now used though the whole app
class Foo {
}

class MyActivity extends RoboActivity {
    @Inject Foo foo; // this will basically call new Foo();
}

注意：这个单例一旦创建会一直驻留内存，其他类似的还有@ContextSingleton,@FragmentSingletion，他们的作用范围比较小，利于垃圾回收。

自定义Binding

public interface IFoo {}

public class Foo implements IFoo {}

public class MyActivity extends RoboActivity {
    //How to tell RoboGuice to inject an instance of Foo ?
    @Inject IFoo foo;
}

要想注入时绑定接口IFoo到Foo，实例化Foo.需要进行绑定。

步骤：

1.向AndroidManifest.xml中添加meta-data

<application ...>
    <meta-data android:name="roboguice.modules"
               android:value="com.example.MyModule,com.example.MyModule2" />                
</application>

2.继承AbstractModule

public class MyModule extends AbstractModule { 
    //a default constructor is fine for a Module

    public void bind() {
        bind(IFoo.class).to(Foo.class);
    }
}

public class MyModule2 extends AbstractModule {
    //if your module requires a context, add a constructor that will be passed a context.
    private Context context;

    //with RoboGuice 3.0, the constructor for AbstractModule will use an `Application`, not a `Context`
    public MyModule( Context context ) {
        this.context = context;
    }

    public void bind() {
        bind(IFoo.class).toInstance( new Foo(context));
    }
}

注入到Service与BroadcastReceiver:

public class MyService extends RoboService {

   @Inject ComputeFooModule computeFooModule;

public class MyBroadcastReceiver extends RoboBroadcastReceiver {

   @Inject ComputeFooModule computeFooModule;

注入到自定义View

class MyView extends View {
    @Inject Foo foo; 
    @InjectView(R.id.my_view) TextView myView;

    public MyView(Context context) {
        inflate(context,R.layout.my_layout, this);
        RoboGuice.getInjector(getContext()).injectMembers(this);//注意这一行，为了使其正常工作。
    }

    public MyView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        inflate(context,R.layout.my_layout, this);
        RoboGuice.getInjector(getContext()).injectMembers(this);
    }

    public MyView(Context context, AttributeSet attrs) {
    super(context, attrs);
        inflate(context,R.layout.my_layout, this);
        RoboGuice.getInjector(getContext()).injectMembers(this);
    }

    @Override
    public void onFinishInflate() {
        super.onFinishInflate();
        //All injections are available from here
        //in both cases of XML and programmatic creations (see below)
        myView.setText(foo.computeFoo());
    }
}

使用RoboGuice Event

public class MyActivity extends RoboActivity {

    // Any method with void return type and a single parameter with @Observes annotation
    // can be used as an event listener.  This one listens to onResume.    
    public void doSomethingOnResume( @Observes OnResumeEvent onResume ) {
        Ln.d("Called doSomethingOnResume in onResume");
    }

    // As you might expect, some events can have parameters.  The OnCreate event
    // has the savedInstanceState parameter that Android passes to onCreate(Bundle)
    public void doSomethingElseOnCreate( @Observes OnCreateEvent onCreate ) {
        Ln.d("onCreate savedInstanceState is %s", onCreate.getSavedInstanceState())
   }

    // And of course, you can have multiple listeners for a given event.
    // Note that ordering of listener execution is indeterminate!
    public void xxx( @Observes OnCreateEvent onCreate ) {
        Ln.d("Hello, world!")
    }
}

本文还有很多特性没有介绍到，后续可能会进行补充。

参考：

http://www.oschina.net/p/roboguice

https://github.com/roboguice/roboguice/wiki

http://mobile.51cto.com/abased-426620.htm