Android進階值探究ActivityLifecycleCallbacks
阿新 • • 發佈：2019-01-01
1 ActivityLifecycleCallbacks用來監聽所有Activity的生命週期回撥
Activity 的每一個生命週期都對應 ActivityLifecycleCallbacks 介面中的一個方法，比如 onActivityCreated 回撥是在 Activity 的 onCreate 方法中呼叫 getApplication().dispatchActivityCreated(this, savedInstanceState) 完成對 Activity 生命週期跟蹤監聽。
public interface ActivityLifecycleCallbacks { void onActivityCreated(Activity activity, Bundle savedInstanceState); void onActivityStarted(Activity activity); void onActivityResumed(Activity activity); void onActivityPaused(Activity activity); void onActivityStopped(Activity activity); void onActivitySaveInstanceState(Activity activity, Bundle outState); void onActivityDestroyed(Activity activity); }
2 ActivityLifecycleCallbacks使用
/** * 要求 API 14+ */ public class MainApplication extends Application { @Override public void onCreate() { super.onCreate(); // AppLifecycleCallback實現ActivityLifecycleCallbacks介面方法 this.registerActivityLifecycleCallbacks(new CustomActivityLifecycleCallback()); } }
3 探究在Android中的應用
- 判斷應用在前後臺
- 管理Activity頁面棧
- 獲取當前Activity頁面
- 儲存恢復狀態值 savedInstanceState
- 應用新開程序假重啟處理（低記憶體回收、修改許可權）
- 頁面分析統計埋點
3.1 判斷應用在前後臺
判斷應用是否在後臺執行，針對前後臺執行會做一些處理，比如：實現從後臺任務恢復啟動（熱啟動）、提示使用者應用執行在後臺、以及應用前後臺切換回調通知等。業務場景非常多，對於開發而言就是提供穩定可靠的檢測前後臺方法，避免出現機型不相容問題。
/** * 自定義生命週期回撥，判斷是否從後臺任務恢復啟動（以實現從後臺任務恢復啟動為例） */ public class CustomActivityLifecycleCallback implements Application.ActivityLifecycleCallbacks { private static final String TAG = "CustomActivityLifecycleCallback"; /** * 處於後臺5分鐘 跳到啟動頁 */ private static long JUMP_SPLASH_GAP = 5 * 60 * 1000; private final Object mActivityLock = new Object(); /** * 記錄Started +1、Stopped -1後是否等0，判斷是否退出到後臺 */ private int mStartStopedCount = 0; /** * 是否是推送等其他的冷啟動 */ private boolean mIsOtherStart = false; private long mLastEndAppTime; @Override public void onActivityCreated(Activity activity, Bundle savedInstanceState) { } @Override public void onActivityStarted(Activity activity) { if (activity == null) { return; } synchronized (mActivityLock) { // 排除：正常冷啟動、熱啟動、推送等其他冷啟動，才是：從後臺任務恢復的啟動 if (!(activity instanceof SplashActivity) && mIsOtherStart && mStartStopedCount == 0) { checkNeedStartSplashActivity(activity); } mStartStopedCount++; } } private void checkNeedStartSplashActivity(Activity activity) { if (mStartStopedCount == 0 && mIsOtherStart && (System.currentTimeMillis() - mLastEndAppTime) > JUMP_SPLASH_GAP) { SplashHotActivity.actionStart(activity); } } @Override public void onActivityResumed(Activity activity) { } @Override public void onActivityPaused(Activity activity) { } @Override public void onActivityStopped(Activity activity) { synchronized (mActivityLock) { mStartStopedCount--; if (mStartStopedCount == 0) { // 下次啟動時，從後臺恢復 mIsOtherStart = true; mLastEndAppTime = System.currentTimeMillis(); } } } @Override public void onActivitySaveInstanceState(Activity activity, Bundle outState) { } @Override public void onActivityDestroyed(Activity activity) { } }
/**
* 後臺任務恢復啟動閃屏頁，區別於SplashActivity頁面的神策統計
*/
public class SplashHotActivity extends SplashActivity {
public static void actionStart(Context context) {
if (context == null) {
return;
}
Intent intent = new Intent(context, SplashHotActivity.class);
intent.putExtra(BUNDLE_KEY_START_FROM_BACK, true);
context.startActivity(intent);
}
}
3.2 管理Activity頁面棧
Activity頁面棧，最常用的實現就是用來完全退出應用。ActivityLifecycleCallbacks和Stack來管理所有的Activity，不僅方便集中管理儲存Activity例項，也不容易造成記憶體洩露。監聽回撥方法onActivityCreated和 onActivityDestroyed 新增刪除Actvity例項。
// CustomActivityLifecycleCallback.java
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
ActivityStackManager.getInstance().addActivity(activity);
}
@Override
public void onActivityDestroyed(Activity activity) {
ActivityStackManager.getInstance().removeActivity(activity);
}
// ActivityStackManager.java
public void addActivity(Activity activity){
if (activities == null) {
activities = new Stack<Activity>();
}
if (activities.search(activity) == -1) {
activities.push(activity);
}
}
public void removeActivity(Activity activity){
if (activities != null && activities.size()>0){
activities.remove(activity);
}
}
3.3 獲取當前Activity頁面
經常需要獲取當前的 TopActivity 例項，用來彈出安全鍵盤、RN介面通訊等。關於獲取當前Activity的一些思考，結合具體實現，推薦兩個實現思路：** 弱引用持有當前Activity例項和Activity頁面棧方式。**
（1）CustomActivityLifecycleCallback.java
// CustomActivityLifecycleCallback.java
@Override
public void onActivityResumed(Activity activity) {
// 弱引用持有當前 Activity 例項
ActivityStackManager.getInstance().setCurrentActivity(activity);
// Activity 頁面棧方式
ActivityStackManager.getInstance().setTopActivity(activity);
}
（2）為什麼Activity頁面棧方式還需要在onActivityResumed中設定當前Activity頁面？
答疑：當關閉B頁面返回A頁面時，首先A頁面的onResume會先執行，然後才會呼叫 B 頁面的onDestroy。
（3）ActivityStackManager獲取當前Activity頁面
// ActivityStackManager.java
private WeakReference<Activity> sCurrentActivityWeakRef;
public Activity getCurrentActivity() {
Activity currentActivity = null;
if (sCurrentActivityWeakRef != null) {
currentActivity = sCurrentActivityWeakRef.get();
}
return currentActivity;
}
public void setCurrentActivity(Activity activity) {
sCurrentActivityWeakRef = new WeakReference<Activity>(activity);
}
public Activity getTopActivity(){
if (activities != null && activities.size() > 0) {
return activities.peek();
}
return null;
}
public void setTopActivity(Activity activity){
if (activities != null && activities.size() > 0) {
if (activities.search(activity) == -1) {
activities.push(activity);
return;
}
int location = activities.search(activity);
if (location != 1) {
activities.remove(activity);
activities.push(activity);
}
}
}
3.4 儲存恢復狀態值savedInstanceState
// CustomActivityLifecycleCallback.java
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
if (savedInstanceState != null && savedInstanceState.getBoolean("saveStateKey", false)) {
Log.e(TAG, "localTime --> " + savedInstanceState.getLong("localTime"));
}
}
@Override
public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
outState.putBoolean("saveStateKey", true);
outState.putLong("localTime", System.currentTimeMillis());
}