Lifecycle介紹

Lifecycle組件屬于Jetpack的架構(gòu)組件中晃听，它是一個(gè)生命周期感知組件安裝官方文檔的說(shuō)明,它可以感知Activity和Fragment生命周期的變化卷拘，這樣子可以讓Activity和Fragment的代碼更為的精簡(jiǎn)，而且一些生命周期的處理就可以單獨(dú)的放在一個(gè)類里去處理了。

Lifecycle官方文檔介紹

Lifecycle的基本使用

使用Lifecycle需要在app的build.gradle文件下進(jìn)行導(dǎo)入承匣，詳細(xì)請(qǐng)看Lifecycle導(dǎo)入說(shuō)明充尉。

//版本號(hào)請(qǐng)查看官方說(shuō)明
implementation "android.arch.lifecycle:extensions:2.1.0"

然后我們創(chuàng)建一個(gè)類繼承LifecycleObserver接口，這就是一個(gè)觀察生命周期的接口只盹，代碼如下所示：

public class MyObserver implements LifecycleObserver {

    private static final String TAG = "MainActivity";

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    public void onStart() {
        Log.i(TAG, "Lifecycle onStart生命周期");
    }


    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    public void onCreate() {
        Log.i(TAG, "Lifecycle onCreate生命周期");
    }


    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    public void onResume() {
        Log.i(TAG, "Lifecycle onResume生命周期");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    public void onPause() {
        Log.i(TAG, "Lifecycle onPause生命周期");
    }


    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    protected void onStop() {
        Log.i("MainActivity","Lifecycle onStop生命周期");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    public void onDestory() {
        Log.i(TAG, "Lifecycle onDestory生命周期");
    }

}

我們可以使用注解在每個(gè)方法上標(biāo)記相應(yīng)的生命周期辣往，這樣就可以去調(diào)用了，接著我們要在需要監(jiān)聽的Activity和Fragment下去進(jìn)行添加監(jiān)聽（被觀察者）：

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //添加監(jiān)聽
        getLifecycle().addObserver(new MyObserver());
        Log.i("MainActivity","Activity onCreate");
    }


    @Override
    protected void onStart() {
        super.onStart();
        Log.i("MainActivity","Activity onStart");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.i("MainActivity","Activity onResume");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.i("MainActivity","Activity onDestroy");
    }


    @Override
    protected void onPause() {
        super.onPause();
        Log.i("MainActivity","Activity onPause");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.i("MainActivity","Activity onStop");
    }
}

在Android Support Library 26.1.0及其之后的版本殖卑，Activity和Fragment已經(jīng)默認(rèn)實(shí)現(xiàn)了LifecycleOwner接口站削，也就是被觀察者，所以我們可以直接調(diào)用getLifecycle()來(lái)進(jìn)行添加觀察者孵稽。運(yùn)行結(jié)果如下：

生命周期監(jiān)聽結(jié)果

關(guān)于自定義LifecycleOwner

剛剛也說(shuō)過(guò)了Activity和Fragment已經(jīng)默認(rèn)實(shí)現(xiàn)了LifecycleOwner接口猛频，但是我們也可以自定義一個(gè)LifecycleOwner狮崩，我們要通過(guò)LifecycleRegistry去進(jìn)行注冊(cè)，LifecycleRegistry是Lifecycle的子類鹿寻。LifecycleRegistry主要是控制LifecycleOwner的狀態(tài)以及狀態(tài)切換睦柴，按照官方文檔的代碼如下：

public class TwoActivity extends AppCompatActivity {


    private LifecycleRegistry lifecycleRegistry;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_two);

        //注冊(cè)
        lifecycleRegistry = new LifecycleRegistry(this);
        lifecycleRegistry.markState(Lifecycle.State.CREATED);
    }


    @Override
    protected void onStart() {
        super.onStart();
        lifecycleRegistry.markState(Lifecycle.State.STARTED);
        Log.i("TwoActivity","Activity onStart");
    }


    @NonNull
    @Override
    public Lifecycle getLifecycle() {
        return lifecycleRegistry;
    }
}

但是你會(huì)發(fā)現(xiàn)一個(gè)問題lifecycleRegistry.markState()竟然是一個(gè)廢棄方法，而且跑起來(lái)是會(huì)報(bào)錯(cuò)的毡熏。

廢棄方法

報(bào)錯(cuò)如圖

lifecycleRegistry.setCurrentState(Lifecycle.State.CREATED);

• 使用生命周期感知型組件處理生命周期