Android基礎#36：Android傳回鍵與Home鍵差別，以及Application的registerActivityLifecycleCallbacks

1. 内容簡介：

在Android系統中，activity是由framework層建立的，而且，由framework管理這activity的生命周期。了解app中各個Actiivty的生命周期，對于開發Android應用程式至關重要。

那麼，當activty進行切換的時候，如何知道相關activity的狀态（生命周期相關函數的調用）呢？可以通過App的registerActivityLifecycleCallbacks來實作。

當按下Android傳回鍵或Home鍵，activity生命周期是如何執行的呢？

2. Android傳回鍵與Home鍵對activity生命周期的影響：

在Android中，當按下Home鍵，預設情況下stop前台的actiity，即activity設定成onstop，而不是ondestory。如果再次啟動該activity不是調用onCreate，而是調用onSavedInstanceState方法，保持上次Activity的狀态則是從onRestart開始->onStart->onResume;

而當按下back鍵則不同，back鍵預設finish前台的activity，即activity的狀态為onDestory為止，再次啟動該activity則從onCreate開始，不會調用onSavedInstanceState方法。

3. Application的registerActivityLifecycleCallbacks：注冊Activity生命周期回調函數

功能：通過注冊Application的registerActivityLifecycleCallbacks，可以監聽Acitivty的生命周期相關函數的調用情況。

代碼如下：

package com.test.myapplication5;


import android.app.Activity;
import android.app.Application;
import android.os.Bundle;
import android.util.Log;


public class MyApp extends Application {
    private static final String TAG = "MainApplication";
    private static MyApp appInstance;


    public static Application getAppInstance() {
        return appInstance;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        Log.i(TAG, "===onCreate======");
        appInstance = this;

        registActivityLife();
    }



    private void registActivityLife() {

        this.registerActivityLifecycleCallbacks(new Application.ActivityLifecycleCallbacks() {

            @Override
            public void onActivityCreated(Activity activity, Bundle bundle) {
                Log.i(TAG, "[registActivityLife] onActivityCreated activity " + activity.getLocalClassName());
            }

            @Override
            public void onActivityStarted(Activity activity) {
                Log.i(TAG, "[registActivityLife] onActivityStarted activity " + activity.getLocalClassName());
            }

            @Override
            public void onActivityResumed(Activity activity) {
                Log.i(TAG, "[registActivityLife] onActivityResumed activity " + activity.getLocalClassName());
            }

            @Override
            public void onActivityPaused(Activity activity) {
                Log.i(TAG, "[registActivityLife] onActivityPaused activity " + activity.getLocalClassName());

            }

            @Override
            public void onActivityStopped(Activity activity) {
                Log.i(TAG, "[registActivityLife] onActivityStopped activity " + activity.getLocalClassName());

            }

            @Override
            public void onActivitySaveInstanceState(Activity activity, Bundle bundle) {
                Log.i(TAG, "[registActivityLife] onActivitySaveInstanceState activity " + activity.getLocalClassName());

            }

            @Override
            public void onActivityDestroyed(Activity activity) {
                Log.i(TAG, "[registActivityLife] onActivityDestroyed activity " + activity.getLocalClassName());
            }
        });
    }
}
           

運作結果：

28755-28755/com.test.myapplication5 I/MainApplication: [registActivityLife] onActivityCreated activity MainActivity
28755-28755/com.test.myapplication5 I/MainApplication: [registActivityLife] onActivityStarted activity MainActivity
28755-28755/com.test.myapplication5 I/MainApplication: [registActivityLife] onActivityResumed activity MainActivity
28755-28755/com.test.myapplication5 I/MainApplication: [registActivityLife] onActivityPaused activity MainActivity

28755-28755/com.test.myapplication5 I/MainApplication: [registActivityLife] onActivityCreated activity activity.MyBrowserActivity2
28755-28755/com.test.myapplication5 I/MainApplication: [registActivityLife] onActivityStarted activity activity.MyBrowserActivity2
28755-28755/com.test.myapplication5 I/MainApplication: [registActivityLife] onActivityResumed activity activity.MyBrowserActivity2
28755-28755/com.test.myapplication5 I/MainApplication: [registActivityLife] onActivityStopped activity MainActivity
28755-28755/com.test.myapplication5 I/MainApplication: [registActivityLife] onActivitySaveInstanceState activity MainActivity
           

相關activity的代碼略。