When we develop an Android application, we always start from the onCreate()
method of the main activity. It is obvious that there are some initializations that should be done before calling onCreate()
. My question is: what is the entrypoint point (or the main
method) of an Android application? What does the Dalvik VM invoke in the very beginning (i.e., when it finishes initialization of its own, and is about to transfer control to the application)? Where can I find the code of this main
?
The first "entry" point is the application class as Kingston pointed out.
However, the easiest thing to get the very first starting point is to check the stack when debugging onCreate.
You may check Instrumentation, this sound somewhat like what you want.
http://developer.android.com/reference/android/app/Instrumentation.html
MainActivity.onCreate(Bundle) line: 12
Instrumentation.callActivityOnCreate(Activity, Bundle) line: 1047
ActivityThread.performLaunchActivity(ActivityThread$ActivityRecord, Intent) line: 2627
ActivityThread.handleLaunchActivity(ActivityThread$ActivityRecord, Intent) line: 2679
ActivityThread.access$2300(ActivityThread, ActivityThread$ActivityRecord, Intent) line: 125
ActivityThread$H.handleMessage(Message) line: 2033
ActivityThread$H(Handler).dispatchMessage(Message) line: 99
Looper.loop() line: 123
ActivityThread.main(String[]) line: 4627
Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]
Method.invoke(Object, Object...) line: 521
ZygoteInit$MethodAndArgsCaller.run() line: 868
ZygoteInit.main(String[]) line: 626
NativeStart.main(String[]) line: not available [native method]
You should extend the Application class and override the onCreate method.
For reference:Application class
I don't know it myself, but it sounds an interesting question. This is the code that fires a new Activity
and following the code, you'll end up in JNI code
public void startActivityForResult(Intent intent, int requestCode) {
if (mParent == null) {
Instrumentation.ActivityResult ar =
mInstrumentation.execStartActivity(
this, mMainThread.getApplicationThread(), mToken, this,
intent, requestCode);
if (ar != null) {
mMainThread.sendActivityResult(
mToken, mEmbeddedID, requestCode, ar.getResultCode(),
ar.getResultData());
}
if (requestCode >= 0) {
// If this start is requesting a result, we can avoid making
// the activity visible until the result is received. Setting
// this code during onCreate(Bundle savedInstanceState) or onResume() will keep the
// activity hidden during this time, to avoid flickering.
// This can only be done when a result is requested because
// that guarantees we will get information back when the
// activity is finished, no matter what happens to it.
mStartedActivity = true;
}
} else {
mParent.startActivityFromChild(this, intent, requestCode);
}
}
Android source code is available, but it's a bit tricky to get it because it's poorly documented. You'll have to install repo
and then download the framework/base
project
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