Annotation注解APT(四):依赖注入框架Dagger

来源：互联网发布：普通用户 linux 知乎编辑：程序博客网时间：2024/06/08 17:58

引言
通过前面的（http://blog.csdn.net/xuewend/article/details/73511128）文章，知道了注解的作用，其中一种就是做依赖注入，dagger是依赖注入的一种框架，那么如何来使用dagger框架呢？

Android Studio中的配置
top build.gradle

// Top-level build file where you can add configuration options common to all sub-projects/modules.buildscript {    repositories {        jcenter()    }    dependencies {        classpath 'com.android.tools.build:gradle:2.3.3'        //添加apt插件        classpath 'com.neenbedankt.gradle.plugins:android-apt:1.8'        // NOTE: Do not place your application dependencies here; they belong        // in the individual module build.gradle files    }}allprojects {    repositories {        jcenter()    }}task clean(type: Delete) {    delete rootProject.buildDir}

app build.gradle

//添加apt注解插件apply plugin: 'com.neenbedankt.android-apt'dependencies {    compile fileTree(dir: 'libs', include: ['*.jar'])    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {        exclude group: 'com.android.support', module: 'support-annotations'    })    compile 'com.android.support:appcompat-v7:25.3.1'    compile 'com.android.support.constraint:constraint-layout:1.0.0-alpha7'    testCompile 'junit:junit:4.12'    //添加dagger依赖的库，当前版本为2.4    compile 'com.google.dagger:dagger:2.4'    apt 'com.google.dagger:dagger-compiler:2.4'}

实例

package com.example.fishmov.daggerdemo;import javax.inject.Inject;/** * Created by fishmov on 17-6-21. */public class People {    private String name = "";    @Inject    public People() {    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}

package com.example.fishmov.daggerdemo;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import javax.inject.Inject;public class MainActivity extends AppCompatActivity {    private static final String TAG = "fish---";    @Inject    People people;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Log.i(TAG, "onCreate: " + people);    }}

直接运行，结果为：

06-21 15:35:36.818 26506-26506/com.example.fishmov.daggerdemo I/fish—: onCreate: null

因为我们目前的@Inject只是一个注解，并没有解析器来解析它，所以加不加一样，people没有初始化当然为空．

我们的目的是通过dagger框架在MainActivity自动注入依赖的People实例，要实现这个还需要一个桥梁Componet，通过Componet来注入：

package com.example.fishmov.daggerdemo;import dagger.Component;/** * Created by fishmov on 17-6-21. */@Componentpublic interface MainComponet {    //定义注入的方法,表示支持对某个类的注入    void inject(MainActivity activity);}

记得rebuild一下，将自动生成Dagger+MainComponet一个类．

package com.example.fishmov.daggerdemo;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import javax.inject.Inject;public class MainActivity extends AppCompatActivity {    private static final String TAG = "fish---";    @Inject    People people;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Log.i(TAG, "onCreate: " + people);        DaggerMainComponet.builder().build().inject(this);        Log.i(TAG, "onCreate: " + people);    }}

直接运行，结果为：

com.example.fishmov.daggerdemo I/fish—: onCreate: null
com.example.fishmov.daggerdemo I/fish—: onCreate: com.example.fishmov.daggerdemo.People@9af3aad

可以看到，调用dagger注入后，people实例化了一个对象．这种注入方式是最基本的注入方式，
然而这并没有什么卵用.
通过这种方式注入，需要在类的构造方法中添加@Inject注解，有时候我们无法修改别人的构造方法的时候，要如何使用注入呢？这个时候就需要@Module和@Provides注解了．

实例

package com.example.fishmov.daggerdemo;import javax.inject.Inject;/** * Created by fishmov on 17-6-21. */public class People {    private String name = "";    public People() {    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}

package com.example.fishmov.daggerdemo;import dagger.Component;/** * Created by fishmov on 17-6-21. */@Component(modules = MainModule.class)public interface MainComponet {    //定义注入的方法,表示支持对某个类的注入    void inject(MainActivity activity);}

package com.example.fishmov.daggerdemo;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import javax.inject.Inject;public class MainActivity extends AppCompatActivity {    private static final String TAG = "fish---";    @Inject    People people;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Log.i(TAG, "onCreate: " + people);        DaggerMainComponet.builder().mainModule(new MainModule()).build().inject(this);        Log.i(TAG, "onCreate: " + people);    }}

直接运行输出：

I/fish—: onCreate: null
I/fish—: onCreate: com.example.fishmov.daggerdemo.People@9af3aad

整个过程可以归纳为以下步骤：

Activity中通过DaggerXXXComponent的Inject()触发注入过程；

Dagger在Activity中搜索用@Inject标注的变量，说明该对象需要被注入；

去Component中注册的Module中搜索注入类；

在Module中搜索返回值为注入类的方法，执行并拿到注入类对象，从而完成注入过程；

如果在Module中没有搜索到提供目标类注入的方法，则在工程中搜索目标类；

找到需要注入对象后，寻找该对象中用@Inject标识的构造方法，完成自动创建过程．

如果People类的构造方法需要参数怎么办？如下：

package com.example.fishmov.daggerdemo;import javax.inject.Inject;/** * Created by fishmov on 17-6-21. */public class People {    private String name = "";    public People(String name) {        this.name = name;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}

package com.example.fishmov.daggerdemo;import dagger.Module;import dagger.Provides;/** * Created by fishmov on 17-6-21. */@Module   //提供依赖对象的实例public class MainModule {    @Provides  // 关键字，标明该方法提供依赖对象    People providerPerson(String name){        //提供Person对象        return new People(name);    }    @Provides    String providerName(){        return "zhangsan";    }　　//或者使用这种　　//@Provides  // 关键字，标明该方法提供依赖对象   //People providerPerson(){        //提供Person对象    //    return new People(＂zhangsan＂);    //}}

package com.example.fishmov.daggerdemo;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import javax.inject.Inject;public class MainActivity extends AppCompatActivity {    private static final String TAG = "fish---";    @Inject    People people;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Log.i(TAG, "onCreate: " + people);        DaggerMainComponet.builder().mainModule(new MainModule()).build().inject(this);        Log.i(TAG, "onCreate: " + people.getName());    }}

直接运行输出：

I/fish—: onCreate: null
I/fish—: onCreate: zhangsan

如果想注入同一对象的多个实例怎么办？这个时候就需要
@Named

package com.example.fishmov.daggerdemo;import javax.inject.Named;import dagger.Module;import dagger.Provides;/** * Created by fishmov on 17-6-21. */@Module   //提供依赖对象的实例public class MainModule {    @Named("a")    @Provides  // 关键字，标明该方法提供依赖对象    People providerPersonA(){        //提供Person对象        return new People("张三");    }    @Named("b")    @Provides  // 关键字，标明该方法提供依赖对象    People providerPersonB(){        //提供Person对象        return new People("李四");    }}

package com.example.fishmov.daggerdemo;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import javax.inject.Inject;import javax.inject.Named;public class MainActivity extends AppCompatActivity {    private static final String TAG = "fish---";    @Named("a")    @Inject    People peopleA;    @Named("b")    @Inject    People peopleB;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        DaggerMainComponet.builder().mainModule(new MainModule()).build().inject(this);        Log.i(TAG, "onCreate: " + peopleA.getName());        Log.i(TAG, "onCreate: " + peopleB.getName());    }}

运行结果：

I/fish—: onCreate: 张三
I/fish—: onCreate: 李四

＠Named注解表示采用使用module中的哪个provides，看看＠Named的代码：

@Qualifier@Documented@Retention(RUNTIME)public @interface Named {    /** The name. */    String value() default "";}

可以看出value是String类型的，前面学过如何自定义注解(http://blog.csdn.net/xuewend/article/details/73507725)，我们也可以自定义一个，来达到和＠Named一样的效果，关键字段
@Qualifier

package com.example.fishmov.daggerdemo;import java.lang.annotation.Documented;import java.lang.annotation.Retention;import javax.inject.Qualifier;import static java.lang.annotation.RetentionPolicy.RUNTIME;/** * Created by fishmov on 17-6-21. */@Qualifier@Documented@Retention(RUNTIME)public @interface MType {    int value() default -1;}

package com.example.fishmov.daggerdemo;import javax.inject.Named;import dagger.Module;import dagger.Provides;/** * Created by fishmov on 17-6-21. */@Module   //提供依赖对象的实例public class MainModule {    @MType(1)    @Provides  // 关键字，标明该方法提供依赖对象    People providerPersonA(){        //提供Person对象        return new People("张三");    }    @MType(2)    @Provides  // 关键字，标明该方法提供依赖对象    People providerPersonB(){        //提供Person对象        return new People("李四");    }}

package com.example.fishmov.daggerdemo;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import javax.inject.Inject;import javax.inject.Named;public class MainActivity extends AppCompatActivity {    private static final String TAG = "fish---";    @MType(1)    @Inject    People peopleA;    @MType(2)    @Inject    People peopleB;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        DaggerMainComponet.builder().mainModule(new MainModule()).build().inject(this);        Log.i(TAG, "onCreate: " + peopleA.getName());        Log.i(TAG, "onCreate: " + peopleB.getName());    }}

运行结果不变．

@Singleton注解
如果我们把peopleB　peopleA都注解为@MType(1)

package com.example.fishmov.daggerdemo;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import javax.inject.Inject;import javax.inject.Named;public class MainActivity extends AppCompatActivity {    private static final String TAG = "fish---";    @MType(1)    @Inject    People peopleA;    @MType(1)    @Inject    People peopleB;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        DaggerMainComponet.builder().mainModule(new MainModule()).build().inject(this);        Log.i(TAG, peopleA.getName() + peopleA);        Log.i(TAG, peopleB.getName() + peopleB);    }}

运行效果：

I/fish—: 张三com.example.fishmov.daggerdemo.People@9af3aad
I/fish—: 张三com.example.fishmov.daggerdemo.People@24ae1e2

可以看出，名字一样，但是地址不同，如果在module中添加@Singleton

package com.example.fishmov.daggerdemo;import javax.inject.Named;import javax.inject.Singleton;import dagger.Module;import dagger.Provides;/** * Created by fishmov on 17-6-21. */@Module   //提供依赖对象的实例public class MainModule {    @Singleton    @MType(1)    @Provides  // 关键字，标明该方法提供依赖对象    People providerPersonA(){        //提供Person对象        return new People("张三");    }    @MType(2)    @Provides  // 关键字，标明该方法提供依赖对象    People providerPersonB(){        //提供Person对象        return new People("李四");    }}

同样，这里也要添加@Singleton

package com.example.fishmov.daggerdemo;import javax.inject.Singleton;import dagger.Component;/** * Created by fishmov on 17-6-21. */@Singleton@Component(modules = MainModule.class)public interface MainComponet {    //定义注入的方法,表示支持对某个类的注入    void inject(MainActivity activity);}

MainActivity不变，直接运行输出：

I/fish—: 张三com.example.fishmov.daggerdemo.People@9af3aad
I/fish—: 张三com.example.fishmov.daggerdemo.People@9af3aad

可以看出地址一样，这就是单例．
但是单例是有作用范围的，比如：

package com.example.fishmov.daggerdemo;import javax.inject.Singleton;import dagger.Component;/** * Created by fishmov on 17-6-21. */@Singleton@Component(modules = MainModule.class)public interface MainComponet {    //定义注入的方法,表示支持对某个类的注入    void inject(MainActivity activity);    //定义注入的方法,表示支持对某个类的注入    void inject(MainActivity.House house);}

package com.example.fishmov.daggerdemo;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import javax.inject.Inject;import javax.inject.Named;public class MainActivity extends AppCompatActivity {    private static final String TAG = "fish---";    @MType(1)    @Inject    People peopleA;    @MType(1)    @Inject    People peopleB;    MainModule mainModule;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mainModule = new MainModule();        DaggerMainComponet.builder().mainModule(mainModule).build().inject(this);        Log.i(TAG, peopleA.getName() + peopleA);        Log.i(TAG, peopleB.getName() + peopleB);        new House();    }    class House{        @MType(1)        @Inject        People peopleA;        @MType(1)        @Inject        People peopleB;        public House() {            DaggerMainComponet.builder().mainModule(mainModule).build().inject(this);            Log.i(TAG + "House", peopleA.getName() + peopleA);            Log.i(TAG + "House", peopleB.getName() + peopleB);        }    }}

结果输出：

I/fish—: 张三com.example.fishmov.daggerdemo.People@e7e1ddb
I/fish—: 张三com.example.fishmov.daggerdemo.People@e7e1ddb
I/fish—House: 张三com.example.fishmov.daggerdemo.People@b2da078
I/fish—House: 张三com.example.fishmov.daggerdemo.People@b2da078

可以看出，同一个Componet注入的地址一样，不同的地址不一样，这叫做假单例，那如何做到全局的单例呢？

package com.example.fishmov.daggerdemo;import android.app.Application;/** * Created by fishmov on 17-6-21. */public class MyApplication extends Application {    private static MainComponet mainComponet;    @Override    public void onCreate() {        super.onCreate();        mainComponet = DaggerMainComponet.builder().mainModule(new MainModule()).build();    }    public static MainComponet getMainComponet() {        return mainComponet;    }}

<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="com.example.fishmov.daggerdemo">    <application        android:name=".MyApplication"        android:allowBackup="true"        android:icon="@mipmap/ic_launcher"        android:label="@string/app_name"        android:roundIcon="@mipmap/ic_launcher_round"        android:supportsRtl="true"        android:theme="@style/AppTheme">        <activity android:name=".MainActivity">            <intent-filter>                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>        </activity>    </application></manifest>

package com.example.fishmov.daggerdemo;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import javax.inject.Inject;import javax.inject.Named;public class MainActivity extends AppCompatActivity {    private static final String TAG = "fish---";    @MType(1)    @Inject    People peopleA;    @MType(1)    @Inject    People peopleB;    MainModule mainModule;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        MyApplication.getMainComponet().inject(this);        Log.i(TAG, peopleA.getName() + peopleA);        Log.i(TAG, peopleB.getName() + peopleB);        new House();    }    class House{        @MType(1)        @Inject        People peopleA;        @MType(1)        @Inject        People peopleB;        public House() {            MyApplication.getMainComponet().inject(this);            Log.i(TAG + "House", peopleA.getName() + peopleA);            Log.i(TAG + "House", peopleB.getName() + peopleB);        }    }}

结果输出：

I/fish—: 张三com.example.fishmov.daggerdemo.People@9af3aad
I/fish—: 张三com.example.fishmov.daggerdemo.People@9af3aad
I/fish—House: 张三com.example.fishmov.daggerdemo.People@9af3aad
I/fish—House: 张三com.example.fishmov.daggerdemo.People@9af3aad

可以看出地址一样了

@Scope注解
@Scope注解相对于@Singleton，和@Qualifier相对于＠Named一样，
看源码：

@Scope@Documented@Retention(RUNTIME)public @interface Singleton {}

所以我们也可以通过@Scope自定义一个注解功能和@Singleton一样．
好了，就到这里吧，其实没有什么卵用．

参考：
http://blog.csdn.net/lylodyf/article/details/52981910?locationNum=8&fps=1
http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2016/0528/4307.html
https://wenku.baidu.com/view/9b6be73515791711cc7931b765ce0508763275cd.html?from=search

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