Android lifecycle 實戰及使用進階

前言

Android lifecycle 使用詳解

Android LiveData 使用詳解

Android lifecyle 源碼解剖

Android livedata 源碼解剖

Android lifecycle 實戰及使用進階

github sample 地址： ArchiteComponentsSample

Android Architecture Components 的，前面咱們已經講解了 lifecycle， LiveData 的使用及原理，今天，讓咱們一塊兒賴看看 lifecycle 在項目中的實戰。主要講解兩點

1. LifecycleHandler 的封裝
2. MVP 中引入 lifecycle，能夠自行監聽 activity 生命週期變化

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LifecycleHandle 的封裝

咱們平時在使用 handler 的時候，在 activity onDestroy 的時候，須要手動取 removeMessage 或者 removeCallBack，否則的話，很容易發生內存泄漏。

@Override
protected void onDestroy() {
    super.onDestroy();
    mHandler.removeCallbacksAndMessages(null);
}

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這對咱們開發者來講，很明顯是一個重複的動做。咱們一塊兒經過 lifecycle 來減小這種重複性的動做，讓其內部本身釋放。

核心原理其實很簡單，內部監聽 activity 生命週期的變化，在 onDestroy 的時候移除 message 和 callback。

public class LifecycleHandler extends Handler implements FullLifecycleObserver {


    private LifecycleOwner mLifecycleOwner;

    public LifecycleHandler(LifecycleOwner lifecycleOwner) {
        mLifecycleOwner = lifecycleOwner;
        addObserver();
    }

    public LifecycleHandler(LifecycleOwner lifecycleOwner, Callback callback) {
        super(callback);
        mLifecycleOwner = lifecycleOwner;
        addObserver();
    }

    public LifecycleHandler(LifecycleOwner lifecycleOwner, Looper looper) {
        super(looper);
        mLifecycleOwner = lifecycleOwner;
        addObserver();
    }

    public LifecycleHandler(LifecycleOwner lifecycleOwner, Looper looper, Callback callback) {
        super(looper, callback);
        mLifecycleOwner = lifecycleOwner;
        addObserver();
    }

    private void addObserver() {
        if (mLifecycleOwner != null) {
            mLifecycleOwner.getLifecycle().addObserver(new FullLifecycleObserverAstrong textdapter(mLifecycleOwner, this));
        }
    }


    @Override
    public void onCreate(LifecycleOwner owner) {

    }

    @Override
    public void onStart(LifecycleOwner owner) {

    }

    @Override
    public void onResume(LifecycleOwner owner) {

    }

    @Override
    public void onPause(LifecycleOwner owner) {

    }

    @Override
    public void onStop(LifecycleOwner owner) {

    }

    @Override
    public void onDestroy(LifecycleOwner owner) {
        removeCallbacksAndMessages(null);
    }
}
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咱們來看一下這一行代碼

mLifecycleOwner.getLifecycle().addObserver(new FullLifecycleObserverAdapter(mLifecycleOwner, this));
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FullLifecycleObserverAdapter 是什麼呢？

FullLifecycleObserverAdapter

public class FullLifecycleObserverAdapter implements LifecycleObserver {

    private final FullLifecycleObserver mObserver;

    private static final String TAG = "FullLifecycleObserverAd";
    private final LifecycleOwner mLifecycleOwner;

    FullLifecycleObserverAdapter(LifecycleOwner lifecycleOwner, FullLifecycleObserver observer) {
        mLifecycleOwner = lifecycleOwner;
        mObserver = observer;
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    public void onCreate() {
        Log.i(TAG, "onCreate: ");
        mObserver.onCreate(mLifecycleOwner);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    public void onStart() {
        Log.i(TAG, "onStart: ");
        mObserver.onStart(mLifecycleOwner);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    public void onResume() {
        Log.i(TAG, "onResume: ");
        mObserver.onResume(mLifecycleOwner);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    public void onPause() {
        Log.i(TAG, "onPause: ");
        mObserver.onPause(mLifecycleOwner);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    public void onStop() {
        Log.i(TAG, "onStop: ");
        mObserver.onStop(mLifecycleOwner);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    public void onDestroy() {
        Log.i(TAG, "onDestroy: ");
        mObserver.onDestroy(mLifecycleOwner);
    }

}
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FullLifecycleObserver

public interface FullLifecycleObserver extends LifecycleObserver {

    void onCreate(LifecycleOwner owner);

    void onStart(LifecycleOwner owner);

    void onResume(LifecycleOwner owner);

    void onPause(LifecycleOwner owner);

    void onStop(LifecycleOwner owner);

    void onDestroy(LifecycleOwner owner);
}
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FullLifecycleObserver 是咱們本身自定義的一個接口，繼承 LifecycleObserver，各個方法一一對應 activity 的生命週期。

FullLifecycleObserverAdapter 實現了 LifecycleObserver，使用了 @OnLifecycleEvent 註解，在 activity 生命週期變化的時候會回調相應的方法，咱們再在裏面回調 observer 的 onCreate， onStart 等方法，這有點相似代理模式。調用關係總結以下：

之後想觀察 lifecycle 生命週期變化的話，只須要 mLifecycleOwner.getLifecycle().addObserver(new FullLifecycleObserverAdapter(mLifecycleOwner, this)); 這一行代碼便可

有人可能會這樣問了，爲何要這樣設計呢

加 FullLifecycleObserver 這個接口，主要是爲了跟 activity 的生命週期一一對應。

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LifecyclePresenter 的封裝

public class LifecyclePresenter implements IPresenter, FullLifecycleObserver {

    private static final String TAG = "BasePresenter";

    private final LifecycleOwner mLifecycleOwner;

    public LifecyclePresenter(LifecycleOwner lifecycleOwner) {
        mLifecycleOwner = lifecycleOwner;
        mLifecycleOwner.getLifecycle().addObserver(new FullLifecycleObserverAdapter(lifecycleOwner, this));
    }

    @Override
    public void onCreate(LifecycleOwner owner) {
        Log.i(TAG, "onCreate: owner = " + owner);
    }

    @Override
    public void onStart(LifecycleOwner owner) {
        Log.i(TAG, "onStart: owner = " + owner);
    }

    @Override
    public void onResume(LifecycleOwner owner) {
        Log.i(TAG, "onResume: owner = " + owner);
    }

    @Override
    public void onPause(LifecycleOwner owner) {
        Log.i(TAG, "onPause: owner = " + owner);
    }

    @Override
    public void onStop(LifecycleOwner owner) {
        Log.i(TAG, "onStop: owner = " + owner);
    }

    @Override
    public void onDestroy(LifecycleOwner owner) {
        Log.i(TAG, "onDestroy: owner = " + owner);
    }
}
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Android 技術人，一位不羈的碼農。