image.png
目录
activity的启动流程（一）
activity的启动流程（二）
activity的启动流程（三）
activity的启动介绍
整个 startActivity 的流程分为 3 大部分，也涉及 3 个进程之间的交互：
- ActivityA --> ActivityManagerService（简称 AMS）
- ActivityManagerService --> ApplicationThread
- ApplicationThread --> Activity
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ActivityA --> ActivityManagerService
在android中，使用startActivity函数启动另一个activity时候，实际执行的代码如下：
/**
* Same as {@link #startActivity(Intent, Bundle)} with no options
* specified.
*
* @param intent The intent to start.
*
* @throws android.content.ActivityNotFoundException
*
* @see #startActivity(Intent, Bundle)
* @see #startActivityForResult
*/
@Override
public void startActivity(Intent intent) {
this.startActivity(intent, null);
}
/**
* Launch a new activity. You will not receive any information about when
* the activity exits. This implementation overrides the base version,
* providing information about
* the activity performing the launch. Because of this additional
* information, the {@link Intent#FLAG_ACTIVITY_NEW_TASK} launch flag is not
* required; if not specified, the new activity will be added to the
* task of the caller.
*
* <p>This method throws {@link android.content.ActivityNotFoundException}
* if there was no Activity found to run the given Intent.
*
* @param intent The intent to start.
* @param options Additional options for how the Activity should be started.
* See {@link android.content.Context#startActivity(Intent, Bundle)}
* Context.startActivity(Intent, Bundle)} for more details.
*
* @throws android.content.ActivityNotFoundException
*
* @see #startActivity(Intent)
* @see #startActivityForResult
*/
@Override
public void startActivity(Intent intent, @Nullable Bundle options) {
if (options != null) {
startActivityForResult(intent, -1, options);
} else {
// Note we want to go through this call for compatibility with
// applications that may have overridden the method.
startActivityForResult(intent, -1);
}
}
/**
* Same as calling {@link #startActivityForResult(Intent, int, Bundle)}
* with no options.
*
* @param intent The intent to start.
* @param requestCode If >= 0, this code will be returned in
* onActivityResult() when the activity exits.
*
* @throws android.content.ActivityNotFoundException
*
* @see #startActivity
*/
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode) {
startActivityForResult(intent, requestCode, null);
}
/**
* @hide
*/
@Override
public void startActivityForResult(
String who, Intent intent, int requestCode, @Nullable Bundle options) {
Uri referrer = onProvideReferrer();
if (referrer != null) {
intent.putExtra(Intent.EXTRA_REFERRER, referrer);
}
options = transferSpringboardActivityOptions(options);
Instrumentation.ActivityResult ar =
mInstrumentation.execStartActivity(
this, mMainThread.getApplicationThread(), mToken, who,
intent, requestCode, options);
if (ar != null) {
mMainThread.sendActivityResult(
mToken, who, requestCode,
ar.getResultCode(), ar.getResultData());
}
cancelInputsAndStartExitTransition(options);
}
可以看出，内部真正执行的是mInstrumentation.execStartActivity函数。
mInstrumentation在Activity类中的声明：
// set by the thread after the constructor and before onCreate(Bundle savedInstanceState) is called.
private Instrumentation mInstrumentation;
进入mInstrumentation源码，看一下execStartActivity函数实现：
/**
* Execute a startActivity call made by the application. The default
* implementation takes care of updating any active {@link ActivityMonitor}
* objects and dispatches this call to the system activity manager; you can
* override this to watch for the application to start an activity, and
* modify what happens when it does.
*
* <p>This method returns an {@link ActivityResult} object, which you can
* use when intercepting application calls to avoid performing the start
* activity action but still return the result the application is
* expecting. To do this, override this method to catch the call to start
* activity so that it returns a new ActivityResult containing the results
* you would like the application to see, and don't call up to the super
* class. Note that an application is only expecting a result if
* <var>requestCode</var> is >= 0.
*
* <p>This method throws {@link android.content.ActivityNotFoundException}
* if there was no Activity found to run the given Intent.
*
* @param who The Context from which the activity is being started.
* @param contextThread The main thread of the Context from which the activity
* is being started.
* @param token Internal token identifying to the system who is starting
* the activity; may be null.
* @param target Which activity is performing the start (and thus receiving
* any result); may be null if this call is not being made
* from an activity.
* @param intent The actual Intent to start.
* @param requestCode Identifier for this request's result; less than zero
* if the caller is not expecting a result.
* @param options Addition options.
*
* @return To force the return of a particular result, return an
* ActivityResult object containing the desired data; otherwise
* return null. The default implementation always returns null.
*
* @throws android.content.ActivityNotFoundException
*
* @see Activity#startActivity(Intent)
* @see Activity#startActivityForResult(Intent, int)
* @see Activity#startActivityFromChild
*
* {@hide}
*/
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, Bundle options) {
IApplicationThread whoThread = (IApplicationThread) contextThread;
Uri referrer = target != null ? target.onProvideReferrer() : null;
if (referrer != null) {
intent.putExtra(Intent.EXTRA_REFERRER, referrer);
}
if (mActivityMonitors != null) {
synchronized (mSync) {
final int N = mActivityMonitors.size();
for (int i=0; i<N; i++) {
final ActivityMonitor am = mActivityMonitors.get(i);
ActivityResult result = null;
if (am.ignoreMatchingSpecificIntents()) {
result = am.onStartActivity(intent);
}
if (result != null) {
am.mHits++;
return result;
} else if (am.match(who, null, intent)) {
am.mHits++;
if (am.isBlocking()) {
return requestCode >= 0 ? am.getResult() : null;
}
break;
}
}
}
}
try {
intent.migrateExtraStreamToClipData();
intent.prepareToLeaveProcess(who);
int result = ActivityManager.getService()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
checkStartActivityResult(result, intent);
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
return null;
}
可以看出，从ActivityMonitor类中调用 ActivityManager.getService()
.startActivity函数。继续跟踪。
ActivityManager类：
/**
* @hide
*/
public static IActivityManager getService() {
return IActivityManagerSingleton.get();
}
private static final Singleton<IActivityManager> IActivityManagerSingleton =
new Singleton<IActivityManager>() {
@Override
protected IActivityManager create() {
final IBinder b = ServiceManager.getService(Context.ACTIVITY_SERVICE);
final IActivityManager am = IActivityManager.Stub.asInterface(b);
return am;
}
};
可以看出getService就是调用AIDL，执行到ActivityManagerService。
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