---
title: 'Activity 狀態 - 儲存時機'
disqus: kyleAlien
---

Activity 狀態 - 儲存時機
===

## OverView of Content

Activity 被系統強制回收時，會觸發 `onSaveInstanceState`，再次開啟時又會觸發 `onRestoreInstanceState` 生命週期

其主要設計是使用了 [**Memo 設計模式**](https://hackmd.io/sLPWDFoqQJW39j2QgNFbZg?view#OverView-of-Content) (請點連結查看)，這裡主要分析這兩個生命週期被觸發的時機點

[TOC]

## AMS 與 Activity 狀態關係

系統在回收指定 App 之前，會將該應用的 Activity 狀態傳給 AMS 儲存，在需要恢復時再透過 AMS 傳遞儲存好的訊息給 App

### [Activity](https://cs.androidom/android/platform/superproject/+/master:frameworks/base/core/java/android/app/Activity.java) 呼叫 onSaveInstanceState 時機

* AMS 在需要暫停 Activity 時會透過 [**ClientTransactionHandler**](https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/java/android/app/ClientTransactionHandler.java)(抽象) 控制，在 Pause 時會呼叫 ClientTransactionHandler#`handlePauseActivity` 方法

    // ActivityThread.java

        @Override
        public void handlePauseActivity(ActivityClientRecord r, boolean finished, boolean userLeaving,
                int configChanges, PendingTransactionActions pendingActions, String reason) {
            if (userLeaving) {
                performUserLeavingActivity(r);
            }

            r.activity.mConfigChangeFlags |= configChanges;
            performPauseActivity(r, finished, reason, pendingActions);

            // Make sure any pending writes are now committed.
            if (r.isPreHoneycomb()) {
                QueuedWork.waitToFinish();
            }
            mSomeActivitiesChanged = true;
        }

* **performStopActivityInner 方法**：從這裡就可以看出，Activity#onSaveInstanceState 方法會在 Activity#onPause 之前被呼叫
> 

    // ActivityThread.java

    private Bundle performPauseActivity(ActivityClientRecord r, boolean finished, String reason,
            PendingTransactionActions pendingActions) {
        if (r.paused) {
            if (r.activity.mFinished) {
                // Activity 已經 Finish，則不進行多於操作
                return null;
            }
            RuntimeException e = new RuntimeException(
                    "Performing pause of activity that is not resumed: "
                    + r.intent.getComponent().toShortString());
            Slog.e(TAG, e.getMessage(), e);
        }
        if (finished) {
            r.activity.mFinished = true;
        }

        // Pre-Honeycomb apps always save their state before pausing
        final boolean shouldSaveState = !r.activity.mFinished && r.isPreHoneycomb();
        
        // 狀態儲存
        if (shouldSaveState) {
            callActivityOnSaveInstanceState(r);
        }

        // onPause 方法
        performPauseActivityIfNeeded(r, reason);

        ... 省略部分

        return shouldSaveState ? r.state : null;
    }

最終 **透過 Instrumentation 呼叫到 Activity#onSaveInstanceState 方法**

    // Instrumentation.java

        private void callActivityOnSaveInstanceState(ActivityClientRecord r) {
            // 將新的 Bundle 資料存到 ActivityClientRecord 中
            r.state = new Bundle();
            r.state.setAllowFds(false);
            if (r.isPersistable()) {
                r.persistentState = new PersistableBundle();
                mInstrumentation.callActivityOnSaveInstanceState(r.activity, r.state,
                        r.persistentState);
            } else {
                mInstrumentation.callActivityOnSaveInstanceState(r.activity, r.state);
            }
        }

### [Activity](https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/java/android/app/Activity.java) 呼叫 onRestoreInstanceState 時機

* AMS 在需要啟動 Activity 時會透過 [**ClientTransactionHandler**](https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/java/android/app/ClientTransactionHandler.java)(抽象) 控制，在 Start 時會呼叫 ClientTransactionHandler#`handleStartActivity` 方法

* **performLaunchActivity 方法**：從這裡就可以看出，Activity#onRestoreInstanceState 方法會在 Activity#onStart 之前被呼叫
> 

    // ActivityThread.java

        
        @Override
        public void handleStartActivity(ActivityClientRecord r,
                PendingTransactionActions pendingActions, ActivityOptions activityOptions) {
            final Activity activity = r.activity;
            
            if (!r.stopped) {
                // 只有 stop 狀態才可以呼叫 start
                throw new IllegalStateException("Can't start activity that is not stopped.");
            }
            
            // Activity finish 則返回
            if (r.activity.mFinished) {
                // TODO(lifecycler): How can this happen?
                return;
            }

            ...

            // 呼叫 Activity#onStart 方法
            activity.performStart("handleStartActivity");
            r.setState(ON_START);

            // Restore instance state
            if (pendingActions.shouldRestoreInstanceState()) {
                if (r.isPersistable()) {
                    ...
                } else if (r.state != null) {
                    mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
                }
            }

            ... 省略部分
        }

最終 **透過 Instrumentation 呼叫到 Activity#onSaveInstanceState 方法**

    // Instrumentation.java

        public void callActivityOnRestoreInstanceState(@NonNull Activity activity,
                @NonNull Bundle savedInstanceState) {
            activity.performRestoreInstanceState(savedInstanceState);
        }

### Activity 生命週期整理

> 

## Appendix & FAQ

:::info
:::

###### tags: `Android Framework`