【android】源码解析——onSaveInstanceState执行时机
之前对于activity的onSaveInstanceState方法的调用时机一直不是很理解，看到一些文章讲过onSaveInstanceState以下5种情况被调用：
- 当用户按下手机home键的时候。
- 长按手机home键或者按下菜单键时。
- 手机息屏时。
- FirstActivity启动SecondActivity，FirstActivity就会调用，也就是说打开新Activity时，原Activity就会调用。
- 默认情况下横竖屏切换时。
本文从源码的角度深入理解下改方法的执行时机。
众所周知，Android通过ActivityThread执行回调activity各个生命周期方法onPause/onStop等等。
通过分析ActivityThread的源码，得到在非人为销毁activity情况下（非按下返回键和调用finish方法情况下）onSaveInstanceState执行。
具体执行时机为：
- targetSdkVersion <（android 11）onPause前执行，
- targetSdkVersion >=（android 11）targetSdkVersion <（android 28） onStop前执行，
- targetSdkVersion >= android 28 onStop后执行。
接下来通过源码具体分析下
handlePauseActivity
@Override
public void handlePauseActivity(IBinder token, boolean finished, boolean userLeaving,
int configChanges, PendingTransactionActions pendingActions, String reason) {
ActivityClientRecord r = mActivities.get(token);
if (r != null) {
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;
}
}
/**
* Pause the activity.
* @return Saved instance state for pre-Honeycomb apps if it was saved, {@code null} otherwise.
*/
private Bundle performPauseActivity(ActivityClientRecord r, boolean finished, String reason,
PendingTransactionActions pendingActions) {
if (r.paused) {
if (r.activity.mFinished) {
// If we are finishing, we won't call onResume() in certain cases.
// So here we likewise don't want to call onPause() if the activity
// isn't resumed.
return null;
}
RuntimeException e = new RuntimeException(
"Performing pause of activity that is not resumed: "
+ r.intent.getComponent().toShortString());
Slog.e(TAG, e.getMessage(), e);
}
//finished入参值通过android native c方法传递进来，在点击返回键和调用activity finish方法时候为true
if (finished) {
r.activity.mFinished = true;
}
// Pre-Honeycomb apps always save their state before pausing
//可以看到android 3.0的判断
final boolean shouldSaveState = !r.activity.mFinished && r.isPreHoneycomb();
if (shouldSaveState) {
callActivityOnSaveInstanceState(r);
}
performPauseActivityIfNeeded(r, reason);
// Notify any outstanding on paused listeners
ArrayList<OnActivityPausedListener> listeners;
synchronized (mOnPauseListeners) {
listeners = mOnPauseListeners.remove(r.activity);
}
int size = (listeners != null ? listeners.size() : 0);
for (int i = 0; i < size; i++) {
listeners.get(i).onPaused(r.activity);
}
...
...
final Bundle oldState = pendingActions != null ? pendingActions.getOldState() : null;
if (oldState != null) {
// We need to keep around the original state, in case we need to be created again.
// But we only do this for pre-Honeycomb apps, which always save their state when
// pausing, so we can not have them save their state when restarting from a paused
// state. For HC and later, we want to (and can) let the state be saved as the
// normal part of stopping the activity.
if (r.isPreHoneycomb()) {
r.state = oldState;
}
}
return shouldSaveState ? r.state : null;
}
可以看到通过handlePauseActivity -> performPauseActivity 定位到在具体执行performPauseActivityIfNeeded之前会调用callActivityOnSaveInstanceState方法只不过需要shouldSaveState为true的情况下。
handleStopActivity
@Override
public void handleStopActivity(IBinder token, boolean show, int configChanges,
PendingTransactionActions pendingActions, boolean finalStateRequest, String reason) {
final ActivityClientRecord r = mActivities.get(token);
r.activity.mConfigChangeFlags |= configChanges;
final StopInfo stopInfo = new StopInfo();
performStopActivityInner(r, stopInfo, show, true /* saveState */, finalStateRequest,
reason);
if (localLOGV) Slog.v(
TAG, "Finishing stop of " + r + ": show=" + show
+ " win=" + r.window);
updateVisibility(r, show);
// Make sure any pending writes are now committed.
if (!r.isPreHoneycomb()) {
QueuedWork.waitToFinish();
}
stopInfo.setActivity(r);
stopInfo.setState(r.state);
stopInfo.setPersistentState(r.persistentState);
pendingActions.setStopInfo(stopInfo);
mSomeActivitiesChanged = true;
}
...
...
/**
* Core implementation of stopping an activity. Note this is a little
* tricky because the server's meaning of stop is slightly different
* than our client -- for the server, stop means to save state and give
* it the result when it is done, but the window may still be visible.
* For the client, we want to call onStop()/onStart() to indicate when
* the activity's UI visibility changes.
* @param r Target activity client record.
* @param info Action that will report activity stop to server.
* @param keepShown Flag indicating whether the activity is still shown.
* @param saveState Flag indicating whether the activity state should be saved.
* @param finalStateRequest Flag indicating if this call is handling final lifecycle state
* request for a transaction.
* @param reason Reason for performing this operation.
*/
private void performStopActivityInner(ActivityClientRecord r, StopInfo info, boolean keepShown,
boolean saveState, boolean finalStateRequest, String reason) {
if (localLOGV) Slog.v(TAG, "Performing stop of " + r);
if (r != null) {
if (!keepShown && r.stopped) {
if (r.activity.mFinished) {
// If we are finishing, we won't call onResume() in certain
// cases. So here we likewise don't want to call onStop()
// if the activity isn't resumed.
return;
}
if (!finalStateRequest) {
final RuntimeException e = new RuntimeException(
"Performing stop of activity that is already stopped: "
+ r.intent.getComponent().toShortString());
Slog.e(TAG, e.getMessage(), e);
Slog.e(TAG, r.getStateString());
}
}
// One must first be paused before stopped...
performPauseActivityIfNeeded(r, reason);
if (info != null) {
try {
// First create a thumbnail for the activity...
// For now, don't create the thumbnail here; we are
// doing that by doing a screen snapshot.
info.setDescription(r.activity.onCreateDescription());
} catch (Exception e) {
if (!mInstrumentation.onException(r.activity, e)) {
throw new RuntimeException(
"Unable to save state of activity "
+ r.intent.getComponent().toShortString()
+ ": " + e.toString(), e);
}
}
}
if (!keepShown) {
callActivityOnStop(r, saveState, reason);
}
}
}
...
...
/**
* Calls {@link Activity#onStop()} and {@link Activity#onSaveInstanceState(Bundle)}, and updates
* the client record's state.
* All calls to stop an activity must be done through this method to make sure that
* {@link Activity#onSaveInstanceState(Bundle)} is also executed in the same call.
*/
private void callActivityOnStop(ActivityClientRecord r, boolean saveState, String reason) {
// Before P onSaveInstanceState was called before onStop, starting with P it's
// called after. Before Honeycomb state was always saved before onPause.
//这里判断调用方法的边界进多了一个saveState和r.state == null saveState在前面performStopActivityInner(r, stopInfo, show, true /* saveState */, finalStateRequest,入参中为true
reason);
final boolean shouldSaveState = saveState && !r.activity.mFinished && r.state == null
&& !r.isPreHoneycomb();
// targetSdkVersion < android P
final boolean isPreP = r.isPreP();
if (shouldSaveState && isPreP) {
callActivityOnSaveInstanceState(r);
}
try {
r.activity.performStop(false /*preserveWindow*/, reason);
} catch (SuperNotCalledException e) {
throw e;
} catch (Exception e) {
if (!mInstrumentation.onException(r.activity, e)) {
throw new RuntimeException(
"Unable to stop activity "
+ r.intent.getComponent().toShortString()
+ ": " + e.toString(), e);
}
}
r.setState(ON_STOP);
// targetSdkVersion >= android P
if (shouldSaveState && !isPreP) {
callActivityOnSaveInstanceState(r);
}
}
通过handleStopActivity -> performStopActivityInner -> callActivityOnStop找到相关调用callActivityOnSaveInstanceState进而进入onSaveInstanceState方法调用。
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