StartActivity的内部代码实现原理
[在此处输入文章标题]
最近研究Android，把StartActiviy的流程研究了一下，特结合代码与大家分享:
1. 首先调用Activity的startActivity，-1表示 target Activity finish的时候不通知original Activity
public
void startActivity(Intent intent) {
startActivityForResult(intent, -1);
}
2 . 调用Activityd的startActivityForResult方法, Instrumentation class 里面有一个ActivityMonitor 的内部类，用来监控view和system的交互
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);
}
}
3. 调用Instrumentation class的 ExecStartActivity：
public
ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder
token, Activity target,
Intent intent, int requestCode) {
IApplicationThread whoThread =
(IApplicationThread) contextThread;
// 如果找到匹配的Activity，am.mHits++
if (mActivityMonitors != null) {
synchronized (mSync) {
final int N =
mActivityMonitors.size();
for (int i=0;
i<N; i++) {
final ActivityMonitor am = mActivityMonitors.get(i);
if
(am.match(who, null, intent)) {
am.mHits++;
if (am.isBlocking()) {
return requestCode >= 0 ? am.getResult() : null;
}
break;
}
}
}
}
try {
//调用ActivityManagerProxy的startActivity方法
int result =
ActivityManagerNative.getDefault()
.startActivity(whoThread, intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
null, 0, token, target != null ? target.mEmbeddedID : null,
requestCode, false, false);
checkStartActivityResult(result,
intent);
} catch (RemoteException e) {
}
return null;
}
4. ActivityManagerProxy 的startActivity的具体实现：
public int startActivity(IApplicationThread caller, Intent
intent,
String resolvedType, Uri[]
grantedUriPermissions, int grantedMode,
IBinder resultTo, String resultWho,
int requestCode, boolean onlyIfNeeded,
boolean debug) throws RemoteException {
// Parcel 本质上把它当成一个Serialize就可以了，只是它是在内存中完成的序列化和反序列化，利用的是连续的内存空间
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(caller != null ? caller.asBinder() :
null);
intent.writeToParcel(data, 0);
data.writeString(resolvedType);
data.writeTypedArray(grantedUriPermissions, 0);
data.writeInt(grantedMode);
data.writeStrongBinder(resultTo);
data.writeString(resultWho);
data.writeInt(requestCode);
data.writeInt(onlyIfNeeded ? 1 : 0);
data.writeInt(debug ? 1 : 0);
//具体请参照后面的代码
mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0);
reply.readException();
int result = reply.readInt();
reply.recycle();
data.recycle();
return result;
}
//清除sOwnedPool中parcel对象，返回一个新的parcel
public static Parcel obtain() {
final Parcel[] pool = sOwnedPool;
synchronized (pool) {
Parcel p;
for (int i=0; i<POOL_SIZE; i++) {
p = pool[i];
if (p != null) {
pool[i] = null;
if (DEBUG_RECYCLE) {
p.mStack = new RuntimeException();
}
return p;
}
}
}
return new Parcel(0);
}
// 清除pool中存储parcel,通过jni free刚才分配的内存
public final void recycle() {
if (DEBUG_RECYCLE) mStack = null;
freeBuffer();
final Parcel[] pool = mOwnObject != 0 ? sOwnedPool : sHolderPool;
synchronized (pool) {
for (int i=0; i<POOL_SIZE; i++) {
if (pool[i] == null) {
pool[i] = this;
return;
}
}
}
}
//
private native void freeBuffer();
//
mRemote 实际通过ActivityManagerNative.getDefault进行注册的，实际就是ActivityManagerService
static public IActivityManager getDefault()
{
if (gDefault != null) {
//if (Config.LOGV) Log.v(
// "ActivityManager", "returning cur default = " + gDefault);
return gDefault;
}
IBinder b = ServiceManager.getService("activity");
if (Config.LOGV) Log.v(
"ActivityManager", "default service binder = " + b);
gDefault = asInterface(b);
if (Config.LOGV) Log.v(
"ActivityManager", "default service = " + gDefault);
return gDefault;
}
5. 实际调用proxy中的Ontransact方法
public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
throws RemoteException {
switch (code) {
case START_ACTIVITY_TRANSACTION:
{
data.enforceInterface(IActivityManager.descriptor);
IBinder b = data.readStrongBinder();
IApplicationThread app = ApplicationThreadNative.asInterface(b);
Intent intent = Intent.CREATOR.createFromParcel(data);
String resolvedType = data.readString();
Uri[] grantedUriPermissions = data.createTypedArray(Uri.CREATOR);
int grantedMode = data.readInt();
IBinder resultTo = data.readStrongBinder();
String resultWho = data.readString();
int requestCode = data.readInt();
boolean onlyIfNeeded = data.readInt() != 0;
boolean debug = data.readInt() != 0;
int result = startActivity(app, intent, resolvedType,
grantedUriPermissions, grantedMode, resultTo, resultWho,
requestCode, onlyIfNeeded, debug);
reply.writeNoException();
reply.writeInt(result);
return true;
}
6 . startActivity 实际调用ActivityManagerService中的startActivity方法
由于StartActivity太长，拿关键部分分享
synchronized(this) {
final long origId = Binder.clearCallingIdentity();
int res = startActivityLocked(caller, intent, resolvedType,
grantedUriPermissions, grantedMode, aInfo,
resultTo, resultWho, requestCode, -1, -1,
onlyIfNeeded, componentSpecified);
Binder.restoreCallingIdentity(origId);
return res;
}
7. startActivityLocked实际调用ApplicationThread中scheduleLaunchActivity
public final void scheduleLaunchActivity(Intent intent, IBinder token,
ActivityInfo info, Bundle state, List<ResultInfo> pendingResults,
List<Intent> pendingNewIntents, boolean notResumed, boolean isForward) {
ActivityRecord r = new ActivityRecord();
r.token = token;
r.intent = intent;
r.activityInfo = info;
r.state = state;
r.pendingResults = pendingResults;
r.pendingIntents = pendingNewIntents;
r.startsNotResumed = notResumed;
r.isForward = isForward;
queueOrSendMessage(H.LAUNCH_ACTIVITY, r);
}
8. queueOrSendMessage 然后发消息给ActivityThread 的Handler
case LAUNCH_ACTIVITY: {
ActivityRecord r = (ActivityRecord)msg.obj;
r.packageInfo = getPackageInfoNoCheck(
r.activityInfo.applicationInfo);
handleLaunchActivity(r);
} break;
具体调用
private final Activity performLaunchActivity(ActivityRecord r) {
// System.out.println("##### [" + System.currentTimeMillis() + "] ActivityThread.performLaunchActivity(" + r + ")");
***
mInstrumentation.callActivityOnCreate(activity, r.state);
***
} catch (SuperNotCalledException e) {
throw e;
} catch (Exception e) {
if (!mInstrumentation.onException(activity, e)) {
throw new RuntimeException(
"Unable to start activity " + component
+ ": " + e.toString(), e);
}
}
return activity;
}
