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Dagger2使用攻略
Dagger2使用攻略
Dagger 2 是 Square 的 Dagger 分支,是一种依赖注入框架。眼下由 Google 接手进行开发,Dagger2是使用代码自己主动生成和手写代码来实现依赖注入。据说在 Dagger 的基础上效率又提升了13%。而且相同功能强大。
1.Gradle配置
(1)须要配置apt 插件:(在project根文件夹build.gradle
文件里加入例如以下代码)
dependencies {
...
classpath ‘com.neenbedankt.gradle.plugins:android-apt:1.8‘
}
(2)加入依赖:(在modulebuild.gradle
文件里加入例如以下代码)
apply plugin: ‘com.neenbedankt.android-apt‘// 凝视处理
dependencies {
...
compile ‘com.google.dagger:dagger:2.0.2‘
apt ‘com.google.dagger:dagger-compiler:2.0.2‘
compile ‘org.glassfish:javax.annotation:10.0-b28‘ // Java标注
}
● 当前最新版本号是2.0.2
● 加入2、3条依赖的原因參考:Dagger2入坑指南
● 假设在项目中同一时候用了Butterknife
,在Build时会报凝视冲突。
解决方法:(在modulebuild.gradle
文件里加入例如以下代码)
packagingOptions {
exclude ‘META-INF/services/javax.annotation.processing.Processor‘
}
(3)最后点击Build-->Make Project
就能够開始使用Dagger2
了。
2.Dagger2 经常使用注解
写了一个简单的Demo,以下依据Demo进行介绍。
Dagger2要理解必须看Dagger 2自己主动生成的代码。Build后代码在
项目-->app-->build-->generated-->source-->apt-->debug
文件夹下。
1.Inject
@Inject
:在须要依赖的地方使用这个注解。告诉Dagger这个类或者字段须要依赖注入,这样Dagger会构造一个这个类实例来满足依赖。
1.构造器注入:首先举一个简单的样例。无參构造方法。
public class Person {
private String name;
private int age;
@Inject
public Person() {
}
public String getName() {
return "Jack";
}
public int getAge() {
return 15;
}
}
这个的局限性是我们不能给这个类中的多个构造器作@Inject
注解。
2.注解成员变量:
接着上面我们要使用这个实例化类。
public class MainActivity extends AppCompatActivity {
@Inject
Person mPerson;
StorageComponent mStorageComponent;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mStorageComponent = ((MyApplication)this.getApplication()).getStorageComponent();
mStorageComponent.inject(this);//注入MainActivity
Toast.makeText(this,mPerson.getName() + "----" +mPerson.getAge(),Toast.LENGTH_SHORT).show();
}
}
这里我们能够查看生成的代码:
@Generated("dagger.internal.codegen.ComponentProcessor")
public final class MainActivity_MembersInjector implements MembersInjector<MainActivity> {
private final MembersInjector<AppCompatActivity> supertypeInjector;
private final Provider<Person> mPersonProvider;
public MainActivity_MembersInjector(MembersInjector<AppCompatActivity> supertypeInjector, Provider<Person> mPersonProvider) {
assert supertypeInjector != null;
this.supertypeInjector = supertypeInjector;
assert mPersonProvider != null;
this.mPersonProvider = mPersonProvider;
}
@Override
public void injectMembers(MainActivity instance) {
if (instance == null) {
throw new NullPointerException("Cannot inject members into a null reference");
}
supertypeInjector.injectMembers(instance);
instance.mPerson = mPersonProvider.get();//这里mPersonProvider替我们实例化了Person
}
public static MembersInjector<MainActivity> create(MembersInjector<AppCompatActivity> supertypeInjector, Provider<Person> mPersonProvider) {
return new MainActivity_MembersInjector(supertypeInjector, mPersonProvider);
}
}
同一时候我们也能够了解到@Inject Person mPerson;
为什么不能使用private
。上面代码中的injectMembers
方法调用后面会说到。
3.方法注入
public class LoginActivityPresenter {
private LoginActivity loginActivity;
@Inject //构造方法注入
public LoginActivityPresenter(LoginActivity loginActivity) {
this.loginActivity = loginActivity;
}
@Inject //方法注入
public void enableWatches(Watches watches) {
watches.register(this);
}
}
如当我们希望传入类的当前实例(this引用)到被注入的依赖中。方法注入会在构造器调用后立即被调用,所以这表示我们能够传入全然被构造的this。
2.Module
@Module
:用来修饰类,表示此类的方法是用来提供依赖的,它告诉Dagger在哪里能够找到依赖。
@Module
public class StorageModule {
private final MyApplication application;
public StorageModule(MyApplication application) {
this.application = application;
}
@Provides
@Singleton
SharedPreferences provideSharedPreferences(){
return PreferenceManager.getDefaultSharedPreferences(application);
}
}
@Provides
以下说到,@Singleton
单例,使用@Singleton
注解之后。对象仅仅会被初始化一次。之后的每次都会被直接注入相同的对象。@Singleton
就是一个内置的作用域。
3.Provides
@Provides
:在@Module
中使用。我们定义的方法用这个注解,用于告诉 Dagger 我们须要构造实例并提供依赖。
为什么要使用@Provides
,由于默认情况下,Dagger满足依赖关系是通过调用构造方法得到的实例,比方上面的Person类使用。可是有时由于@Inject
的局限性。我们不能使用@Inject
。比方构造方法有多个、三方库中的类我们不知道他是怎么实现的等等。比如以下代码中的SharedPreferences
。我们使用@Provides
返回一个创建好的实例,这样做也显得灵活不是吗?
@Provides
@Singleton
SharedPreferences provideSharedPreferences(){
return PreferenceManager.getDefaultSharedPreferences(application);
}
注意:
● 依照习惯 @Providers
方法都会用provide作为前缀,@Module
类都用Module作为后缀。
● 假设@Provides
方法有參数。这个參数也要保证能够被Dagger得到(比如通过其它的@Provides
方法或者@Inject注解的构造方法。)
4.Component
@Component
: 是@Inject
和@Module
的桥梁,须要列出所有的@Modules以组成该组件。
@Singleton
@Component(modules = {
StorageModule.class ,
ScheduleModule.class
})
public interface StorageComponent {
Storage execute();
void inject(MainActivity mMainActivity);
}
Dagger会依照上面接口生成一个实现类。生成类以Dagger为前缀。提供builder()来生成实例。调用方法:(由于是单例,所以这里放到了MyApplication)
public class MyApplication extends Application {
private StorageComponent component;
@Override
public void onCreate() {
super.onCreate();
component = DaggerStorageComponent
.builder()//调用构建类
.storageModule(new StorageModule(this)) //传入Module
.build();//生成实例
}
public StorageComponent getStorageComponent() {
return component;
}
}
MainActivity代码:
public class MainActivity extends AppCompatActivity {
@Bind(R.id.button1)
Button mButton1;
@Bind(R.id.button2)
Button mButton2;
@Inject
SharedPreferences mPreferences;//全局的SharedPreferences
@Inject
Person mPerson;
StorageComponent mStorageComponent;
private final String KEY = "Dagger 2";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.bind(this);
mStorageComponent = ((MyApplication)this.getApplication()).getStorageComponent();
mStorageComponent.inject(this);//注入MainActivity
mStorageComponent.execute().storage();//运行储存操作
}
@OnClick({R.id.button1,R.id.button2})
void onButtonClicked(View v) {
switch (v.getId()) {
case R.id.button1:
Toast.makeText(this,mPreferences.getString(KEY,"---"),Toast.LENGTH_SHORT).show();
//上面是演示样例获取mPreferences,实际中将SharedPreferences操作都能够封装进Storage中。例如以下
//Toast.makeText(this,
//mStorageComponent.execute().getStorage(),Toast.LENGTH_SHORT).show();
break;
case R.id.button2:
Toast.makeText(this,
mPerson.getName() + "----" + mPerson.getAge(),Toast.LENGTH_SHORT).show();
break;
}
}
}
下来把整个流程走一遍:首先进入MyApplication
运行DaggerStorageComponent.builder().storageModule(new StorageModule(this)).build();
方法获取实例化StorageComponent
。那我我们查看DaggerStorageComponent
类:
@Generated("dagger.internal.codegen.ComponentProcessor")
public final class DaggerStorageComponent implements StorageComponent {
private Provider<SharedPreferences> provideSharedPreferencesProvider;
private Provider<ScheduleImpl> provideScheduleProvider;
private Provider<Storage> storageProvider;
private MembersInjector<MainActivity> mainActivityMembersInjector;
private DaggerStorageComponent(Builder builder) {
assert builder != null;
initialize(builder);
}
public static Builder builder() {
return new Builder();
}
private void initialize(final Builder builder) {
this.provideSharedPreferencesProvider = ScopedProvider.create(StorageModule_ProvideSharedPreferencesFactory.create(builder.storageModule));
this.provideScheduleProvider = ScopedProvider.create(ScheduleModule_ProvideScheduleFactory.create(builder.scheduleModule));
this.storageProvider = Storage_Factory.create(provideSharedPreferencesProvider, provideScheduleProvider);
this.mainActivityMembersInjector = MainActivity_MembersInjector.create((MembersInjector) MembersInjectors.noOp(), provideSharedPreferencesProvider, Person_Factory.create());//实例化到这里结束
}
@Override
public Storage execute() {
return storageProvider.get();
}
@Override
public void inject(MainActivity mMainActivity) {
mainActivityMembersInjector.injectMembers(mMainActivity);
}
public static final class Builder {
private StorageModule storageModule;
private ScheduleModule scheduleModule;
private Builder() {
}
public StorageComponent build() {
if (storageModule == null) {
throw new IllegalStateException("storageModule must be set");
}
if (scheduleModule == null) {
this.scheduleModule = new ScheduleModule();
}
return new DaggerStorageComponent(this);
}
public Builder storageModule(StorageModule storageModule) {
if (storageModule == null) {
throw new NullPointerException("storageModule");
}
this.storageModule = storageModule;
return this;
}
public Builder scheduleModule(ScheduleModule scheduleModule) {
if (scheduleModule == null) {
throw new NullPointerException("scheduleModule");
}
this.scheduleModule = scheduleModule;
return this;
}
}
}
上面代码最后运行到MainActivity_MembersInjector.create(…)查看MainActivity_MembersInjector
类:
@Generated("dagger.internal.codegen.ComponentProcessor")
public final class MainActivity_MembersInjector implements MembersInjector<MainActivity> {
private final MembersInjector<AppCompatActivity> supertypeInjector;
private final Provider<SharedPreferences> mPreferencesProvider;
private final Provider<Person> mPersonProvider;
public MainActivity_MembersInjector(MembersInjector<AppCompatActivity> supertypeInjector, Provider<SharedPreferences> mPreferencesProvider, Provider<Person> mPersonProvider) {
assert supertypeInjector != null;
this.supertypeInjector = supertypeInjector;
assert mPreferencesProvider != null;
this.mPreferencesProvider = mPreferencesProvider;
assert mPersonProvider != null;
this.mPersonProvider = mPersonProvider;
}
@Override
public void injectMembers(MainActivity instance) {
if (instance == null) {
throw new NullPointerException("Cannot inject members into a null reference");
}
supertypeInjector.injectMembers(instance);
instance.mPreferences = mPreferencesProvider.get();//赋值
instance.mPerson = mPersonProvider.get();
}
public static MembersInjector<MainActivity> create(MembersInjector<AppCompatActivity> supertypeInjector, Provider<SharedPreferences> mPreferencesProvider, Provider<Person> mPersonProvider) {
return new MainActivity_MembersInjector(supertypeInjector, mPreferencesProvider, mPersonProvider);
}
}
下来进入到了MainActivity
。在通过((MyApplication)this.getApplication()).getStorageComponent()
获取到component
后运行mStorageComponent.inject(this);
方法注入MainActivity,终于回调到上面代码中的injectMembers
方法中。能够看出MainActivity
中的成员变量所有初始完毕。之后就能够直接使用了。
5.Lazy 类
Lazy类是实现懒载入,调用的时候才创建实例,通过Lazy对象实现,得到对象的实例使用get()方法。比如:
public class Storage {
private SharedPreferences mPreferences;
private Lazy<ScheduleImpl> mScheduleImpl;//Lazy 类
private final String KEY = "Dagger 2";
@Inject
public Storage(SharedPreferences mPreferences ,Lazy<ScheduleImpl> mScheduleImpl) {
this.mPreferences = mPreferences;
this.mScheduleImpl = mScheduleImpl;
}
public void storage() {
mScheduleImpl.get().start();//get()方法
mPreferences.edit().putString(KEY, "Dagger 2 -- Example").commit();
mScheduleImpl.get().end();
}
}
6.Scope
@Scope
:注解作用域,通过自己定义注解限定对象的作用范围。它是JSR-330标准的一部分,事实上@Singleton
就是一种@Scope
。
在Dagger 2中,@Scope
被用于标记自己定义的scope注解。简单说它们能够相似单例地标记依赖。
被作注解的依赖会变成单例,可是这会与component的生命周期(不是整个应用)关联。
首先创建一个LoginScope:
@Scope
@Retention(RetentionPolicy.RUNTIME)
public @interface LoginScope {
}
Module:
@Module
public class LoginModule {
@Provides
@LoginScope //<---这里为单例
Person providePerson() {
Person mPerson = new Person();
mPerson.setAge(23);
mPerson.setName("WeiLu");
return mPerson;
}
@Provides
Login provideLogin() {
Login mLogin = new Login();
mLogin.setPassword("######");
mLogin.setName("小关");
return mLogin;
}
}
Component:
@LoginScope
@Component(modules = {
LoginModule.class
})
public interface LoginComponent {
void inject(MyApplication myApplication);
}
调用:
mLoginComponent = DaggerLoginComponent.builder()
.loginModule(new LoginModule())
.build();
mLoginComponent.inject(this);
这里我们看一下生成代码:
@Generated("dagger.internal.codegen.ComponentProcessor")
public final class DaggerLoginComponent implements LoginComponent {
private Provider<Person> providePersonProvider;
private Provider<Login> provideLoginProvider;
private MembersInjector<MyApplication> myApplicationMembersInjector;
private DaggerLoginComponent(Builder builder) {
assert builder != null;
initialize(builder);
}
public static Builder builder() {
return new Builder();
}
public static LoginComponent create() {
return builder().build();
}
private void initialize(final Builder builder) {
this.providePersonProvider = ScopedProvider.create(LoginModule_ProvidePersonFactory.create(builder.loginModule));
this.provideLoginProvider = LoginModule_ProvideLoginFactory.create(builder.loginModule);
this.myApplicationMembersInjector = MyApplication_MembersInjector.create((MembersInjector) MembersInjectors.noOp(), providePersonProvider, provideLoginProvider);
}
@Override
public void inject(MyApplication myApplication) {
myApplicationMembersInjector.injectMembers(myApplication);
}
public static final class Builder {
private LoginModule loginModule;
private Builder() {
}
public LoginComponent build() {
if (loginModule == null) {
this.loginModule = new LoginModule();
}
return new DaggerLoginComponent(this);
}
public Builder loginModule(LoginModule loginModule) {
if (loginModule == null) {
throw new NullPointerException("loginModule");
}
this.loginModule = loginModule;
return this;
}
}
}
看initialize
方法:没有加@LoginScope
的Login类。那么他的创建是就是利用工厂模式new了一个Login。
相反加了@LoginScope
的Person类,是利用ScopedProvider
储存了起来。源代码例如以下:
public final class ScopedProvider<T> implements Provider<T> {
private static final Object UNINITIALIZED = new Object();
private final Factory<T> factory;
private volatile Object instance;
private ScopedProvider(Factory<T> factory) {
this.instance = UNINITIALIZED;
assert factory != null;
this.factory = factory;
}
public T get() {
Object result = this.instance;
if(result == UNINITIALIZED) {
synchronized(this) {
result = this.instance;
if(result == UNINITIALIZED) {
this.instance = result = this.factory.get();
}
}
}
return result;
}
public static <T> Provider<T> create(Factory<T> factory) {
if(factory == null) {
throw new NullPointerException();
} else {
return new ScopedProvider(factory);
}
}
}
7.Qualifier
@Qualifier
:限定符,当类的类型不足以鉴别一个依赖的时候会使用到。假设我们没有去区分,会报错:xxx cannot be provided without an @Provides-annotated method。比如上面的Person类,我们如今准备返回两个:小明与小关。返回的都是Person类,怎么区分依赖?
首先自己定义一个@Qualifier
:
@Qualifier
@Retention(RetentionPolicy.RUNTIME)
public @interface User {
}
下来是Module:
@Module
public class UserModule {
@Provides
@User//加上这个自己定义注解用于区分
Login provideXiaoMingUser() {
Login xiaomin = new Login();
xiaomin.setPassword("******");
xiaomin.setName("小明");
return xiaomin;
}
@Provides
Login provideXiaoGuanUser() {
Login xiaoguan = new Login();
xiaoguan.setPassword("######");
xiaoguan.setName("小关");
return xiaoguan;
}
}
Component:
@Subcomponent(modules = {
UserModule.class
})
public interface UserComponent {
void inject(SecondActivity mSecondActivity);
}
这里用到了@Subcomponent
,我们想复用组件时。能够使用它。以下是父组件用法。还有一种是注解属性加入dependencies。
@Singleton
@Component(
modules ={ AppModule.class
}
)
public interface AppComponent {
Context getAppContext();
UserComponent createUserComponent(UserModule userModule);
}
这样的复用组件事实上是在在父组件中创建了子组件的内部类。例如以下:
@Generated("dagger.internal.codegen.ComponentProcessor")
public final class DaggerAppComponent implements AppComponent {
private Provider<Context> provideContextProvider;
private DaggerAppComponent(Builder builder) {
assert builder != null;
initialize(builder);
}
public static Builder builder() {
return new Builder();
}
private void initialize(final Builder builder) {
this.provideContextProvider = ScopedProvider.create(AppModule_ProvideContextFactory.create(builder.appModule));
}
@Override
public Context getAppContext() {
return provideContextProvider.get();
}
@Override
public UserComponent createUserComponent(UserModule userModule) {
return new UserComponentImpl(userModule);
}
public static final class Builder {
private AppModule appModule;
private Builder() {
}
public AppComponent build() {
if (appModule == null) {
throw new IllegalStateException("appModule must be set");
}
return new DaggerAppComponent(this);
}
public Builder appModule(AppModule appModule) {
if (appModule == null) {
throw new NullPointerException("appModule");
}
this.appModule = appModule;
return this;
}
}
private final class UserComponentImpl implements UserComponent {//内部类
private final UserModule userModule;
private Provider<Login> provideXiaoMingUserProvider;
private Provider<Login> provideXiaoGuanUserProvider;
private MembersInjector<SecondActivity> secondActivityMembersInjector;
private UserComponentImpl(UserModule userModule) {
if (userModule == null) {
throw new NullPointerException();
}
this.userModule = userModule;
initialize();
}
private void initialize() {
this.provideXiaoMingUserProvider = UserModule_ProvideXiaoMingUserFactory.create(userModule);
this.provideXiaoGuanUserProvider = UserModule_ProvideXiaoGuanUserFactory.create(userModule);
this.secondActivityMembersInjector = SecondActivity_MembersInjector.create((MembersInjector) MembersInjectors.noOp(), provideXiaoMingUserProvider, provideXiaoGuanUserProvider);
}
@Override
public void inject(SecondActivity mSecondActivity) {
secondActivityMembersInjector.injectMembers(mSecondActivity);
}
}
}
初始化:(MyApplication中)
mAppComponent = DaggerAppComponent.builder()
.appModule(new AppModule(this))
.build();
mUserComponent = mAppComponent.createUserComponent(new UserModule());
调用:
public class SecondActivity extends AppCompatActivity {
UserComponent userComponent;
@Inject
@User
Login xiaoming;
@Inject
Login xiaoguan;
@Bind(R.id.button4)
Button mButton4;
@Bind(R.id.button5)
Button mButton5;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
ButterKnife.bind(this);
userComponent = ((MyApplication)this.getApplication()).getUserComponent();
userComponent.inject(this);
}
@OnClick({
R.id.button4,
R.id.button5,
})
void onButtonClicked(View v) {
switch (v.getId()) {
case R.id.button4:
Toast.makeText(this,
xiaoming.getName() + "----" + xiaoming.getPassword(),Toast.LENGTH_SHORT).show();
break;
case R.id.button5:
Toast.makeText(this,
xiaoguan.getName() + "----" + xiaoguan.getPassword(),Toast.LENGTH_SHORT).show();
break;
}
}
}
详细生成的代码。大家下载Demo后自行查看。
通过自己主动生成的代码能够看出Dagger 2主要用到了Builder模式、Factory模式。代码不难理解。同一时候由于Dagger 2没有使用反射,尽管效率提高了,可是缺乏灵活性。
这也是为了提高效率的代价。
3.Dagger2 练习Demo
Demo下载链接:Dagger2Example
4.參考
1. Dagger 2 API文档
2. Android Dagger2学习
3. 使用Dagger 2依赖注入 - API
4. Dependency injection with Dagger 2 - Custom scopes
PS:最后说一下,关于Dagger2的学习成本还是挺高的。我自己也是从零開始接触。利用业余时间前前后后用了近一周时间去学习,一開始看的也是云里雾里。
事实上对比着自己主动生成的代码多看看就比較好理解了。有什么错误地方。希望多多交流。就这样。
。。
Dagger2使用攻略