Activity生命周期简介
Activity生命周期如上图所示，详细的介绍可见安卓生命周期官方文档。
本文主要研究Activity的生命周期相关回调方法调用的流程。
ClientTransaction
ClientTransaction定义在frameworks/base/core/java/android/app/servertransaction/ClientTransaction.java中，其定义的成员变量：
/**
* A container that holds a sequence of messages, which may be sent to a client.
* This includes a list of callbacks and a final lifecycle state.
*
* @see com.android.server.am.ClientLifecycleManager
* @see ClientTransactionItem
* @see ActivityLifecycleItem
* @hide
*/
public class ClientTransaction implements Parcelable, ObjectPoolItem {
/** A list of individual callbacks to a client. */
@UnsupportedAppUsage
private List<ClientTransactionItem> mActivityCallbacks;
/**
* Final lifecycle state in which the client activity should be after the transaction is
* executed.
*/
private ActivityLifecycleItem mLifecycleStateRequest;
/** Target client. */
private IApplicationThread mClient;
/** Target client activity. Might be null if the entire transaction is targeting an app. */
private IBinder mActivityToken;
......
}
ClientTransaction的对象从SystemServer进程通过binder调用传给app进程，其中几个重要的成员变量如下：
mClient：代表此ClientTransaction要传给的app进程；
mActivityToken：代表此ClientTransaction要传给的具体Activity；
mActivityCallbacks：表示需要Activity执行的回调，这个回调可能是进入某个生命周期，或者是例如onConfigurationChanged的回调；
mLifecycleStateRequest：表示Activity最终进入的生命周期，其类型ActivityLifecycleItem是ClientTransactionItem的子类，是具体某个生命周期的回调。
frameworks/base/core/java/android/app/servertransaction/BaseClientRequest.java是ClientTransactionItem的父类，其定义：
/**
* Base interface for individual requests from server to client.
* Each of them can be prepared before scheduling and, eventually, executed.
* @hide
*/
public interface BaseClientRequest extends ObjectPoolItem {
/**
* Prepare the client request before scheduling.
* An example of this might be informing about pending updates for some values.
*
* @param client Target client handler.
* @param token Target activity token.
*/
default void preExecute(ClientTransactionHandler client, IBinder token) {
}
/**
* Execute the request.
* @param client Target client handler.
* @param token Target activity token.
* @param pendingActions Container that may have data pending to be used.
*/
void execute(ClientTransactionHandler client, IBinder token,
PendingTransactionActions pendingActions);
/**
* Perform all actions that need to happen after execution, e.g. report the result to server.
* @param client Target client handler.
* @param token Target activity token.
* @param pendingActions Container that may have data pending to be used.
*/
default void postExecute(ClientTransactionHandler client, IBinder token,
PendingTransactionActions pendingActions) {
}
}
frameworks/base/core/java/android/app/servertransaction/ClientTransactionItem.java定义：
/**
* A callback message to a client that can be scheduled and executed.
* Examples of these might be activity configuration change, multi-window mode change, activity
* result delivery etc.
*
* @see ClientTransaction
* @see com.android.server.am.ClientLifecycleManager
* @hide
*/
public abstract class ClientTransactionItem implements BaseClientRequest, Parcelable {
/** Get the state that must follow this callback. */
@LifecycleState
public int getPostExecutionState() {
return UNDEFINED;
}
// Parcelable
@Override
public int describeContents() {
return 0;
}
}
frameworks/base/core/java/android/app/servertransaction/ActivityLifecycleItem.java是ClientTransactionItem的子类，其定义：
/**
* Request for lifecycle state that an activity should reach.
* @hide
*/
public abstract class ActivityLifecycleItem extends ClientTransactionItem {
@IntDef(prefix = { "UNDEFINED", "PRE_", "ON_" }, value = {
UNDEFINED,
PRE_ON_CREATE,
ON_CREATE,
ON_START,
ON_RESUME,
ON_PAUSE,
ON_STOP,
ON_DESTROY,
ON_RESTART
})
@Retention(RetentionPolicy.SOURCE)
public @interface LifecycleState{}
public static final int UNDEFINED = -1;
public static final int PRE_ON_CREATE = 0;
public static final int ON_CREATE = 1;
public static final int ON_START = 2;
public static final int ON_RESUME = 3;
public static final int ON_PAUSE = 4;
public static final int ON_STOP = 5;
public static final int ON_DESTROY = 6;
public static final int ON_RESTART = 7;
/** A final lifecycle state that an activity should reach. */
@LifecycleState
public abstract int getTargetState();
/** Called by subclasses to make sure base implementation is cleaned up */
@Override
public void recycle() {
}
}
SystemServer进程
Activity的onCreate、onStart、onResume等生命周期方法都是由SystemServer进程发起的，调用frameworks/base/services/core/java/com/android/server/wm/ClientLifecycleManager.java的scheduleTransaction方法，此方法有多个重载，可以传入已经构建好了的ClientTransaction对象或传入相应参数在scheduleTransaction方法中构建ClientTransaction对象：
/**
* Class that is able to combine multiple client lifecycle transition requests and/or callbacks,
* and execute them as a single transaction.
*
* @see ClientTransaction
*/
class ClientLifecycleManager {
// TODO(lifecycler): Implement building transactions or global transaction.
// TODO(lifecycler): Use object pools for transactions and transaction items.
/**
* Schedule a transaction, which may consist of multiple callbacks and a lifecycle request.
* @param transaction A sequence of client transaction items.
* @throws RemoteException
*
* @see ClientTransaction
*/
void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
final IApplicationThread client = transaction.getClient();
transaction.schedule();
if (!(client instanceof Binder)) {
// If client is not an instance of Binder - it's a remote call and at this point it is
// safe to recycle the object. All objects used for local calls will be recycled after
// the transaction is executed on client in ActivityThread.
transaction.recycle();
}
}
/**
* Schedule a single lifecycle request or callback to client activity.
* @param client Target client.
* @param activityToken Target activity token.
* @param stateRequest A request to move target activity to a desired lifecycle state.
* @throws RemoteException
*
* @see ClientTransactionItem
*/
void scheduleTransaction(@NonNull IApplicationThread client, @NonNull IBinder activityToken,
@NonNull ActivityLifecycleItem stateRequest) throws RemoteException {
final ClientTransaction clientTransaction = transactionWithState(client, activityToken,
stateRequest);
scheduleTransaction(clientTransaction);
}
/**
* Schedule a single callback delivery to client activity.
* @param client Target client.
* @param activityToken Target activity token.
* @param callback A request to deliver a callback.
* @throws RemoteException
*
* @see ClientTransactionItem
*/
void scheduleTransaction(@NonNull IApplicationThread client, @NonNull IBinder activityToken,
@NonNull ClientTransactionItem callback) throws RemoteException {
final ClientTransaction clientTransaction = transactionWithCallback(client, activityToken,
callback);
scheduleTransaction(clientTransaction);
}
/**
* Schedule a single callback delivery to client application.
* @param client Target client.
* @param callback A request to deliver a callback.
* @throws RemoteException
*
* @see ClientTransactionItem
*/
void scheduleTransaction(@NonNull IApplicationThread client,
@NonNull ClientTransactionItem callback) throws RemoteException {
final ClientTransaction clientTransaction = transactionWithCallback(client,
null /* activityToken */, callback);
scheduleTransaction(clientTransaction);
}
/**
* @return A new instance of {@link ClientTransaction} with a single lifecycle state request.
*
* @see ClientTransaction
* @see ClientTransactionItem
*/
private static ClientTransaction transactionWithState(@NonNull IApplicationThread client,
@NonNull IBinder activityToken, @NonNull ActivityLifecycleItem stateRequest) {
final ClientTransaction clientTransaction = ClientTransaction.obtain(client, activityToken);
clientTransaction.setLifecycleStateRequest(stateRequest);
return clientTransaction;
}
/**
* @return A new instance of {@link ClientTransaction} with a single callback invocation.
*
* @see ClientTransaction
* @see ClientTransactionItem
*/
private static ClientTransaction transactionWithCallback(@NonNull IApplicationThread client,
IBinder activityToken, @NonNull ClientTransactionItem callback) {
final ClientTransaction clientTransaction = ClientTransaction.obtain(client, activityToken);
clientTransaction.addCallback(callback);
return clientTransaction;
}
}
得到构建好了的ClientTransaction对象后，会调用ClientTransaction的schedule方法：
/**
* Schedule the transaction after it was initialized. It will be send to client and all its
* individual parts will be applied in the following sequence:
* 1. The client calls {@link #preExecute(ClientTransactionHandler)}, which triggers all work
* that needs to be done before actually scheduling the transaction for callbacks and
* lifecycle state request.
* 2. The transaction message is scheduled.
* 3. The client calls {@link TransactionExecutor#execute(ClientTransaction)}, which executes
* all callbacks and necessary lifecycle transitions.
*/
public void schedule() throws RemoteException {
mClient.scheduleTransaction(this);
}
App进程
通过binder调用了app进程中frameworks/base/core/java/android/app/ActivityThread.java的内部类ApplicationThread的scheduleTransaction方法：
@Override
public void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
ActivityThread.this.scheduleTransaction(transaction);
}
调用了ActivityThread的父类frameworks/base/core/java/android/app/ClientTransactionHandler.java的scheduleTransaction方法：
/** Prepare and schedule transaction for execution. */
void scheduleTransaction(ClientTransaction transaction) {
transaction.preExecute(this);
sendMessage(ActivityThread.H.EXECUTE_TRANSACTION, transaction);
}
这个消息在ActivityThread的内部类H的handleMessage方法中处理：
public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
switch (msg.what) {
......
case EXECUTE_TRANSACTION:
final ClientTransaction transaction = (ClientTransaction) msg.obj;
mTransactionExecutor.execute(transaction);
if (isSystem()) {
// Client transactions inside system process are recycled on the client side
// instead of ClientLifecycleManager to avoid being cleared before this
// message is handled.
transaction.recycle();
}
// TODO(lifecycler): Recycle locally scheduled transactions.
break;
......
}
调用了frameworks/base/core/java/android/app/servertransaction/TransactionExecutor.java的execute方法：
/**
* Resolve transaction.
* First all callbacks will be executed in the order they appear in the list. If a callback
* requires a certain pre- or post-execution state, the client will be transitioned accordingly.
* Then the client will cycle to the final lifecycle state if provided. Otherwise, it will
* either remain in the initial state, or last state needed by a callback.
*/
public void execute(ClientTransaction transaction) {
if (DEBUG_RESOLVER) Slog.d(TAG, tId(transaction) + "Start resolving transaction");
final IBinder token = transaction.getActivityToken();
if (token != null) {
final Map<IBinder, ClientTransactionItem> activitiesToBeDestroyed =
mTransactionHandler.getActivitiesToBeDestroyed();
final ClientTransactionItem destroyItem = activitiesToBeDestroyed.get(token);
if (destroyItem != null) {
if (transaction.getLifecycleStateRequest() == destroyItem) {
// It is going to execute the transaction that will destroy activity with the
// token, so the corresponding to-be-destroyed record can be removed.
activitiesToBeDestroyed.remove(token);
}
if (mTransactionHandler.getActivityClient(token) == null) {
// The activity has not been created but has been requested to destroy, so all
// transactions for the token are just like being cancelled.
Slog.w(TAG, tId(transaction) + "Skip pre-destroyed transaction:\n"
+ transactionToString(transaction, mTransactionHandler));
return;
}
}
}
if (DEBUG_RESOLVER) Slog.d(TAG, transactionToString(transaction, mTransactionHandler));
executeCallbacks(transaction);
executeLifecycleState(transaction);
mPendingActions.clear();
if (DEBUG_RESOLVER) Slog.d(TAG, tId(transaction) + "End resolving transaction");
}
注意这里首先调用TransactionExecutor的executeCallbacks执行ClientTransaction对象中的所有mActivityCallbacks的回调，然后再调用TransactionExecutor的executeLifecycleState方法进入ClientTransaction对象的目标生命周期mLifecycleStateRequest。
首先来看TransactionExecutor的executeCallbacks方法：
/** Cycle through all states requested by callbacks and execute them at proper times. */
@VisibleForTesting
public void executeCallbacks(ClientTransaction transaction) {
final List<ClientTransactionItem> callbacks = transaction.getCallbacks();
if (callbacks == null || callbacks.isEmpty()) {
// No callbacks to execute, return early.
return;
}
if (DEBUG_RESOLVER) Slog.d(TAG, tId(transaction) + "Resolving callbacks in transaction");
final IBinder token = transaction.getActivityToken();
ActivityClientRecord r = mTransactionHandler.getActivityClient(token);
// In case when post-execution state of the last callback matches the final state requested
// for the activity in this transaction, we won't do the last transition here and do it when
// moving to final state instead (because it may contain additional parameters from server).
final ActivityLifecycleItem finalStateRequest = transaction.getLifecycleStateRequest();
final int finalState = finalStateRequest != null ? finalStateRequest.getTargetState()
: UNDEFINED;
// Index of the last callback that requests some post-execution state.
final int lastCallbackRequestingState = lastCallbackRequestingState(transaction);
final int size = callbacks.size();
for (int i = 0; i < size; ++i) {
final ClientTransactionItem item = callbacks.get(i);
if (DEBUG_RESOLVER) Slog.d(TAG, tId(transaction) + "Resolving callback: " + item);
final int postExecutionState = item.getPostExecutionState();
final int closestPreExecutionState = mHelper.getClosestPreExecutionState(r,
item.getPostExecutionState());
if (closestPreExecutionState != UNDEFINED) {
cycleToPath(r, closestPreExecutionState, transaction);
}
item.execute(mTransactionHandler, token, mPendingActions);
item.postExecute(mTransactionHandler, token, mPendingActions);
if (r == null) {
// Launch activity request will create an activity record.
r = mTransactionHandler.getActivityClient(token);
}
if (postExecutionState != UNDEFINED && r != null) {
// Skip the very last transition and perform it by explicit state request instead.
final boolean shouldExcludeLastTransition =
i == lastCallbackRequestingState && finalState == postExecutionState;
cycleToPath(r, postExecutionState, shouldExcludeLastTransition, transaction);
}
}
}
对每个callbacks中的ClientTransactionItem回调，首先如果需要的话会调用TransactionExecutor的cycleToPath方法让Activity进入最近的前一个生命周期，然后调用ClientTransactionItem的execute方法让Activity进入指定的生命周期或只是执行一个回调。
回到TransactionExecutor的execute方法中，后面还调用了TransactionExecutor的executeLifecycleState方法：
/** Transition to the final state if requested by the transaction. */
private void executeLifecycleState(ClientTransaction transaction) {
final ActivityLifecycleItem lifecycleItem = transaction.getLifecycleStateRequest();
if (lifecycleItem == null) {
// No lifecycle request, return early.
return;
}
final IBinder token = transaction.getActivityToken();
final ActivityClientRecord r = mTransactionHandler.getActivityClient(token);
if (DEBUG_RESOLVER) {
Slog.d(TAG, tId(transaction) + "Resolving lifecycle state: "
+ lifecycleItem + " for activity: "
+ getShortActivityName(token, mTransactionHandler));
}
if (r == null) {
// Ignore requests for non-existent client records for now.
return;
}
// Cycle to the state right before the final requested state.
cycleToPath(r, lifecycleItem.getTargetState(), true /* excludeLastState */, transaction);
// Execute the final transition with proper parameters.
lifecycleItem.execute(mTransactionHandler, token, mPendingActions);
lifecycleItem.postExecute(mTransactionHandler, token, mPendingActions);
}
这里首先调用了TransactionExecutor的cycleToPath方法确保让Activity进入最近的前一个生命周期，然后调用ActivityLifecycleItem的execute方法让Activity进入目标生命周期，最后调用了ActivityLifecycleItem的postExecute方法。
看下TransactionExecutor的cycleToPath方法：
/** Transition the client between states. */
@VisibleForTesting
public void cycleToPath(ActivityClientRecord r, int finish, ClientTransaction transaction) {
cycleToPath(r, finish, false /* excludeLastState */, transaction);
}
/**
* Transition the client between states with an option not to perform the last hop in the
* sequence. This is used when resolving lifecycle state request, when the last transition must
* be performed with some specific parameters.
*/
private void cycleToPath(ActivityClientRecord r, int finish, boolean excludeLastState,
ClientTransaction transaction) {
final int start = r.getLifecycleState();
if (DEBUG_RESOLVER) {
Slog.d(TAG, tId(transaction) + "Cycle activity: "
+ getShortActivityName(r.token, mTransactionHandler)
+ " from: " + getStateName(start) + " to: " + getStateName(finish)
+ " excludeLastState: " + excludeLastState);
}
final IntArray path = mHelper.getLifecyclePath(start, finish, excludeLastState);
performLifecycleSequence(r, path, transaction);
}
调用了TransactionExecutor的performLifecycleSequence方法：
/** Transition the client through previously initialized state sequence. */
private void performLifecycleSequence(ActivityClientRecord r, IntArray path,
ClientTransaction transaction) {
final int size = path.size();
for (int i = 0, state; i < size; i++) {
state = path.get(i);
if (DEBUG_RESOLVER) {
Slog.d(TAG, tId(transaction) + "Transitioning activity: "
+ getShortActivityName(r.token, mTransactionHandler)
+ " to state: " + getStateName(state));
}
switch (state) {
case ON_CREATE:
mTransactionHandler.handleLaunchActivity(r, mPendingActions,
null /* customIntent */);
break;
case ON_START:
mTransactionHandler.handleStartActivity(r.token, mPendingActions);
break;
case ON_RESUME:
mTransactionHandler.handleResumeActivity(r.token, false /* finalStateRequest */,
r.isForward, "LIFECYCLER_RESUME_ACTIVITY");
break;
case ON_PAUSE:
mTransactionHandler.handlePauseActivity(r.token, false /* finished */,
false /* userLeaving */, 0 /* configChanges */, mPendingActions,
"LIFECYCLER_PAUSE_ACTIVITY");
break;
case ON_STOP:
mTransactionHandler.handleStopActivity(r.token, 0 /* configChanges */,
mPendingActions, false /* finalStateRequest */,
"LIFECYCLER_STOP_ACTIVITY");
break;
case ON_DESTROY:
mTransactionHandler.handleDestroyActivity(r.token, false /* finishing */,
0 /* configChanges */, false /* getNonConfigInstance */,
"performLifecycleSequence. cycling to:" + path.get(size - 1));
break;
case ON_RESTART:
mTransactionHandler.performRestartActivity(r.token, false /* start */);
break;
default:
throw new IllegalArgumentException("Unexpected lifecycle state: " + state);
}
}
}
这里的mTransactionHandler其实就是ActivityThread，调用其相应的handleLaunchActivity、handleStartActivity、handleResumeActivity、handlePauseActivity、handleStopActivity、handleDestroyActivity或performRestartActivity方法来进一步调用相应的Activity的生命周期方法。
回到TransactionExecutor的executeLifecycleState方法中，后面会调用ActivityLifecycleItem的execute方法让Activity进入目标生命周期，最后还会调用ActivityLifecycleItem的postExecute，例如这里的ActivityLifecycleItem是frameworks/base/core/java/android/app/servertransaction/ResumeActivityItem.java：
/**
* Request to move an activity to resumed state.
* @hide
*/
public class ResumeActivityItem extends ActivityLifecycleItem {
......
@Override
public void execute(ClientTransactionHandler client, IBinder token,
PendingTransactionActions pendingActions) {
Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, "activityResume");
client.handleResumeActivity(token, true /* finalStateRequest */, mIsForward,
"RESUME_ACTIVITY");
Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);
}
@Override
public void postExecute(ClientTransactionHandler client, IBinder token,
PendingTransactionActions pendingActions) {
try {
// TODO(lifecycler): Use interface callback instead of AMS.
ActivityTaskManager.getService().activityResumed(token);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
......
}
这里传进来的ClientTransactionHandler其实就是ActivityThread，这里也是调用了ActivityThread的handleResumeActivity方法来进一步调用相应的Activity的生命周期方法，那么Activity具体是如何启动的可以看Activity的启动流程。
最后在postExecute方法中会通过binder调用frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java的activityResumed方法通知SystemServer此Activity进入了resume状态。
181
扫一扫
被折叠的 条评论
为什么被折叠?
到【灌水乐园】发言
