聲明 : http://www.reibang.com/p/714062a9af75
目錄

簡(jiǎn)介
原理
使用方法

1,Activty 中使用
2,Fragment 中使用
3,service 中使用
4,Application監(jiān)聽 app 的聲明周期

?? 簡(jiǎn)介:

??LifeCycle可以幫助開發(fā)者創(chuàng)建可感知生命周期的組件,這樣, 組件便能夠在內(nèi)部管理自己的聲明周期,從而降低模塊間的耦合度,并降低內(nèi)存泄漏發(fā)生的可能性.

?? 工作原理:

??Jetpack 為我們提供了兩個(gè)類,LifecycleOwner(被觀察者)和 LifecycleObserver(觀察者).即通過觀察者模式,實(shí)現(xiàn)對(duì)頁面聲明周期的監(jiān)聽.通過源碼可以看出來,Activity 已經(jīng)默認(rèn)實(shí)現(xiàn)了 LifecycleOwner 接口,并提供了一個(gè) getLifecycle(LiftcycleObserver observer)方法,LifecycleOwner 正是通過該方法實(shí)現(xiàn)觀察者模式的.

@RestrictTo(LIBRARY_GROUP_PREFIX)
public class ComponentActivity extends Activity implements
        LifecycleOwner,
        KeyEventDispatcher.Component {
        .......
    /**
     * This is only used for apps that have not switched to Fragments 1.1.0, where this
     * behavior is provided by <code>androidx.activity.ComponentActivity</code>.
     */
    private LifecycleRegistry mLifecycleRegistry = new LifecycleRegistry(this);

     ......

    @CallSuper
    @Override
    protected void onSaveInstanceState(@NonNull Bundle outState) {
        mLifecycleRegistry.markState(Lifecycle.State.CREATED);
        super.onSaveInstanceState(outState);
    }
    ......
}

?? 使用方法:

1,Activty 中使用:

class MainActivity : AppCompatActivity() {
    companion object {
        const val Tag = "MainActivity"

    }

    var myLifeCycle = MyLifeCycle()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
       //將觀察者和被觀察者綁定~~~
        lifecycle.addObserver(myLifeCycle)
        Log.i(Tag, "MainAc---OnCreate")
    }

    override fun onStart() {
        super.onStart()
        Log.i(Tag, "MainAc---onStart")

    }
    //........雷同代碼不再貼出來

}

MyLifeCycle

class MyLifeCycle : LifecycleObserver {
    companion object {
        const val Tag = "MyLifeCycle"
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    fun myLifeOnCreate() {
        Log.d(Tag, "MyLifeCycle---OnCreate")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    fun myLifeonStart() {
        Log.d(Tag, "MyLifeCycle---onStart")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    fun myLifeonResume() {
        Log.d(Tag, "MyLifeCycle---onResume")
    }

   //.....雷同代碼補(bǔ)貼出來了

}

運(yùn)行一下

結(jié)果圖.png

結(jié)果圖 2.png

是不是超級(jí)簡(jiǎn)單啊,????就這樣,LifeCycle 就完美的解決了組件對(duì)生命周期的依賴問題,使組件能夠管理自己的生命周期,降低耦合度.如果與 Activity 數(shù)據(jù)有交互,那就寫一個(gè)接口,回調(diào)一下的啦~~懶了,不想寫代碼了,當(dāng)然了Fragment 同樣的使用方法,看下面

2,Fragment 中使用

class HomeFragment : Fragment() {
    var myLifeCycle = MyLifeCycle()
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        myLifeCycle = MyLifeCycle()
        lifecycle.addObserver(myLifeCycle)
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_home, container, false)
    }
    
}

so easy~~~運(yùn)行結(jié)果截圖就不貼了哈.....因?yàn)閼?

3,service 中使用

Android提供了一個(gè)名為 LifecycleService 的類,該類繼承 Service,并實(shí)現(xiàn)了 LifecycleOwner 的接口,與 Activity/Fragment 類似,也提供了一個(gè) getLifecycle()的方法供我們使用.看下源碼

public class LifecycleService extends Service implements LifecycleOwner {

    private final ServiceLifecycleDispatcher mDispatcher = new ServiceLifecycleDispatcher(this);

    //.........
    @Override
    @NonNull
    public Lifecycle getLifecycle() {
        return mDispatcher.getLifecycle();
    }
}

好了,開始實(shí)現(xiàn)吧.

在 build.gradle 中引用

implementation "androidx.lifecycle:lifecycle-extensions:2.2.0"

然后開擼代碼

class MyService : LifecycleService() {
    companion object {
        const val Tag = "MyService"

    }

    init {
        lifecycle.addObserver(MyLifeCycle())
    }

    override fun onCreate() {
        super.onCreate()
        Log.i(Tag, "MyService---OnCreate")
    }

    override fun onStart(intent: Intent?, startId: Int) {
        super.onStart(intent, startId)
        Log.i(Tag, "MyService---onStart")
    }

    override fun onDestroy() {
        super.onDestroy()
        Log.i(Tag, "MyService---onDestroy")
    }
}

運(yùn)行一下

image.png

完活~
哦,別忘記,清單文件注冊(cè)一下服務(wù)

image.png

4,Application監(jiān)聽 app 的聲明周期

LifeCycle 提供了一個(gè)名為 ProcessLifecycleOwner 的類,以便我們知道整個(gè)程序的聲明周期的情況.
Look下面.
build.gradle 文件

implementation "androidx.lifecycle:lifecycle-extensions:2.2.0"

Application:

class MyApplication : Application() {
    private val Tag = "MyApplication"
    override fun onCreate() {
        super.onCreate()
        Log.i(Tag, "MyApplication---OnCreate")
        ProcessLifecycleOwner.get().lifecycle.addObserver(MyLifeCycle())
    }
}

MyLifeCycle:
重點(diǎn)看注釋,哪些會(huì)被調(diào)用,哪些不會(huì)被調(diào)用

class MyLifeCycle : LifecycleObserver {
    companion object {
        const val Tag = "MyLifeCycle"
    }

    //在應(yīng)用程序整個(gè)聲明周期中只會(huì)被調(diào)用一次
    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    fun myLifeOnCreate() {
        Log.d(Tag, "MyLifeCycle---OnCreate")
    }

    //當(dāng)應(yīng)用程序出現(xiàn)在前臺(tái)是被調(diào)用
    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    fun myLifeonStart() {
        Log.d(Tag, "MyLifeCycle---onStart")
    }

    //當(dāng)應(yīng)用程序出現(xiàn)在前臺(tái)是被調(diào)用
    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    fun myLifeonResume() {
        Log.d(Tag, "MyLifeCycle---onResume")
    }

    //當(dāng)應(yīng)用程序出現(xiàn)退出到后臺(tái)是被調(diào)用
    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    fun myLifeonPause() {
        Log.d(Tag, "MyLifeCycle---onPause")
    }

    //當(dāng)應(yīng)用程序出現(xiàn)退出到后臺(tái)是被調(diào)用
    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    fun myLifeonStop() {
        Log.d(Tag, "MyLifeCycle---onStop")
    }

    //永遠(yuǎn)不會(huì)被調(diào)用,系統(tǒng)不會(huì)分發(fā)調(diào)用ON_DESTROY事件
    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    fun myLifeonDestroy() {
        Log.d(Tag, "MyLifeCycle---onDestroy")
    }
}

運(yùn)行一下

image.png

image.png

END