Plug-in has been widely used in the current mainstream app. Although the scheme is mature, there are still many pits emerging. Here is one of the problems that Jingdongdao has encountered when it is integrated into Jingdongdao App as a plug-in.
0x01. Crash Information Stack
---java.lang.IllegalArgumentException: Wrong state class, expecting View State but received class android.widget.TextView$SavedState instead. This usually happens when two views of different type have the same id in the same hierarchy. This view's id is id/plugin_xxx_voiceButton. Make sure other views do not use the same id.
android.view.View.onRestoreInstanceState(View.java:13827)
android.view.View.dispatchRestoreInstanceState(View.java:13803)
android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2923)
android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2923)
android.view.View.restoreHierarchyState(View.java:13781)
android.support.v4.app.Fragment.restoreViewState(Fragment.java:468)
android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1094)
android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1248)
android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1230)
android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:2042)
android.support.v4.app.FragmentController.dispatchActivityCreated(FragmentController.java:165)
android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:543)
com.xxx.xxx.xxx.activity.xxxActivity.onStart(xxxActivity.java:260)
com.xxx.xxx.xxx.activity.ActivityXXX.onStart(ActivityXXX.java:2302)
android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1245)
com.jingdong.aura.xxx.xxx.xxx.callActivityOnStart(SourceFile:439)
android.app.Activity.performStart(Activity.java:6099)
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2367)
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2466)
android.app.ActivityThread.access$900(ActivityThread.java:175)
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1369)
com.jingdong.aura.xxx.xxx.x$x.handleMessage(xxxFile:47)
android.os.Handler.dispatchMessage(Handler.java:98)
android.os.Looper.loop(Looper.java:135)
android.app.ActivityThread.main(ActivityThread.java:5418)
java.lang.reflect.Method.invoke(Native Method)
java.lang.reflect.Method.invoke(Method.java:372)
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1037)
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832)0x02. analysis
Current View: This view's id is id/plugin_xxx_voiceButton.
Behavior:
expecting View State but received class android.widget.TextView$SavedState instead
V6.5.0 Plug-in before upgrading
public static final int plugin_xxx_firstRightImage = 1208418738;
public static final int plugin_xxx_voiceButton = 1208418739; //ImageButton
public static final int plugin_xxx_inputBox = 1208418740; // extends EditText extends TextView
public static final int plugin_xxx_smileyButton = 1208418741;Upgraded V6.5.0-bu plug-in
public static final int plugin_xxx_firstRightImage = 1208418738;
public static final int plugin_xxx_layout_bottom_btn = 1208418739;
public static final int plugin_xxx_voiceButton = 1208418740; //ImageButton
public static final int plugin_xxx_inputBox = 1208418741; // extends TextViewWhen a user has a problem, the crash message indicates that the upgraded component version number is currently loaded:11
Current view:
voiceButton = 1208418740, but received plugin_xxx_inputBox = 1208418740 (id of previous version, parent type TextView)
0x04. Loading Strategy of Components
Cold start, plug-in update must restart the process to take effect.
0x05. Source code analysis
frameworks/support/v4/java/android/support/v4/app/FragmentActivity.java
/**
* Dispatch onStart() to all fragments. Ensure any created loaders are
* now started.
*/
@Override
protected void onStart() {
super.onStart();
mStopped = false;
mReallyStopped = false;
mHandler.removeMessages(MSG_REALLY_STOPPED);
if (!mCreated) {
mCreated = true;
mFragments.dispatchActivityCreated();
}
mFragments.noteStateNotSaved();
mFragments.execPendingActions();
mFragments.doLoaderStart();
// NOTE: HC onStart goes here.
mFragments.dispatchStart();
mFragments.reportLoaderStart();
}frameworks/support/v4/java/android/support/v4/app/FragmentController.java
/**
* Moves all Fragments managed by the controller's FragmentManager
* into the activity created state.
* <p>Call when Fragments should be informed their host has been created.
*
* @see Fragment#onActivityCreated(Bundle)
*/
public void dispatchActivityCreated() {
mHost.mFragmentManager.dispatchActivityCreated();
}frameworks/support/v4/java/android/support/v4/app/FragmentManager.java
public void dispatchActivityCreated() {
mStateSaved = false;
moveToState(Fragment.ACTIVITY_CREATED, false);
} void moveToState(int newState, boolean always) {
moveToState(newState, 0, 0, always);
}
void moveToState(int newState, int transit, int transitStyle, boolean always) {
if (mHost == null && newState != Fragment.INITIALIZING) {
throw new IllegalStateException("No host");
}
if (!always && mCurState == newState) {
return;
}
mCurState = newState;
if (mActive != null) {
boolean loadersRunning = false;
for (int i=0; i<mActive.size(); i++) {
Fragment f = mActive.get(i);
if (f != null) {
moveToState(f, newState, transit, transitStyle, false);//Processing Fragment Object f
if (f.mLoaderManager != null) {
loadersRunning |= f.mLoaderManager.hasRunningLoaders();
}
}
}
if (!loadersRunning) {
startPendingDeferredFragments();
}
if (mNeedMenuInvalidate && mHost != null && mCurState == Fragment.RESUMED) {
mHost.onSupportInvalidateOptionsMenu();
mNeedMenuInvalidate = false;
}
}
}
//Specific Processing Logic
void moveToState(Fragment f, int newState, int transit, int transitionStyle,
boolean keepActive) {
// Fragments that are not currently added will sit in the onCreate() state.
if ((!f.mAdded || f.mDetached) && newState > Fragment.CREATED) {
newState = Fragment.CREATED;
}
if (f.mRemoving && newState > f.mState) {
// While removing a fragment, we can't change it to a higher state.
newState = f.mState;
}
// Defer start if requested; don't allow it to move to STARTED or higher
// if it's not already started.
if (f.mDeferStart && f.mState < Fragment.STARTED && newState > Fragment.STOPPED) {
newState = Fragment.STOPPED;
}
if (f.mState < newState) {
// For fragments that are created from a layout, when restoring from
// state we don't want to allow them to be created until they are
// being reloaded from the layout.
if (f.mFromLayout && !f.mInLayout) {
return;
}
if (f.mAnimatingAway != null) {
// The fragment is currently being animated... but! Now we
// want to move our state back up. Give up on waiting for the
// animation, move to whatever the final state should be once
// the animation is done, and then we can proceed from there.
f.mAnimatingAway = null;
moveToState(f, f.mStateAfterAnimating, 0, 0, true);
}
switch (f.mState) {
case Fragment.INITIALIZING:
if (DEBUG) Log.v(TAG, "moveto CREATED: " + f);
if (f.mSavedFragmentState != null) {
f.mSavedFragmentState.setClassLoader(mHost.getContext().getClassLoader());
f.mSavedViewState = f.mSavedFragmentState.getSparseParcelableArray(
FragmentManagerImpl.VIEW_STATE_TAG);
f.mTarget = getFragment(f.mSavedFragmentState,
FragmentManagerImpl.TARGET_STATE_TAG);
if (f.mTarget != null) {
f.mTargetRequestCode = f.mSavedFragmentState.getInt(
FragmentManagerImpl.TARGET_REQUEST_CODE_STATE_TAG, 0);
}
f.mUserVisibleHint = f.mSavedFragmentState.getBoolean(
FragmentManagerImpl.USER_VISIBLE_HINT_TAG, true);
if (!f.mUserVisibleHint) {
f.mDeferStart = true;
if (newState > Fragment.STOPPED) {
newState = Fragment.STOPPED;
}
}
}
f.mHost = mHost;
f.mParentFragment = mParent;
f.mFragmentManager = mParent != null
? mParent.mChildFragmentManager : mHost.getFragmentManagerImpl();
f.mCalled = false;
f.onAttach(mHost.getContext());
if (!f.mCalled) {
throw new SuperNotCalledException("Fragment " + f
+ " did not call through to super.onAttach()");
}
if (f.mParentFragment == null) {
mHost.onAttachFragment(f);
} else {
f.mParentFragment.onAttachFragment(f);
}
if (!f.mRetaining) {
f.performCreate(f.mSavedFragmentState);
} else {
f.restoreChildFragmentState(f.mSavedFragmentState);
f.mState = Fragment.CREATED;
}
f.mRetaining = false;
if (f.mFromLayout) {
// For fragments that are part of the content view
// layout, we need to instantiate the view immediately
// and the inflater will take care of adding it.
f.mView = f.performCreateView(f.getLayoutInflater(
f.mSavedFragmentState), null, f.mSavedFragmentState);
if (f.mView != null) {
f.mInnerView = f.mView;
if (Build.VERSION.SDK_INT >= 11) {
ViewCompat.setSaveFromParentEnabled(f.mView, false);
} else {
f.mView = NoSaveStateFrameLayout.wrap(f.mView);
}
if (f.mHidden) f.mView.setVisibility(View.GONE);
f.onViewCreated(f.mView, f.mSavedFragmentState);
} else {
f.mInnerView = null;
}
}
case Fragment.CREATED:
if (newState > Fragment.CREATED) {
if (DEBUG) Log.v(TAG, "moveto ACTIVITY_CREATED: " + f);
if (!f.mFromLayout) {
ViewGroup container = null;
if (f.mContainerId != 0) {
if (f.mContainerId == View.NO_ID) {
throwException(new IllegalArgumentException(
"Cannot create fragment "
+ f
+ " for a container view with no id"));
}
container = (ViewGroup) mContainer.onFindViewById(f.mContainerId);
if (container == null && !f.mRestored) {
String resName;
try {
resName = f.getResources().getResourceName(f.mContainerId);
} catch (NotFoundException e) {
resName = "unknown";
}
throwException(new IllegalArgumentException(
"No view found for id 0x"
+ Integer.toHexString(f.mContainerId) + " ("
+ resName
+ ") for fragment " + f));
}
}
f.mContainer = container;
f.mView = f.performCreateView(f.getLayoutInflater(
f.mSavedFragmentState), container, f.mSavedFragmentState);
if (f.mView != null) {
f.mInnerView = f.mView;
if (Build.VERSION.SDK_INT >= 11) {
ViewCompat.setSaveFromParentEnabled(f.mView, false);
} else {
f.mView = NoSaveStateFrameLayout.wrap(f.mView);
}
if (container != null) {
Animation anim = loadAnimation(f, transit, true,
transitionStyle);
if (anim != null) {
setHWLayerAnimListenerIfAlpha(f.mView, anim);
f.mView.startAnimation(anim);
}
container.addView(f.mView);
}
if (f.mHidden) f.mView.setVisibility(View.GONE);
f.onViewCreated(f.mView, f.mSavedFragmentState);
} else {
f.mInnerView = null;
}
}
f.performActivityCreated(f.mSavedFragmentState);
if (f.mView != null) {
f.restoreViewState(f.mSavedFragmentState); //Here we begin Restore View State
}
f.mSavedFragmentState = null;
}
case Fragment.ACTIVITY_CREATED:
if (newState > Fragment.ACTIVITY_CREATED) {
f.mState = Fragment.STOPPED;
}
case Fragment.STOPPED:
if (newState > Fragment.STOPPED) {
if (DEBUG) Log.v(TAG, "moveto STARTED: " + f);
f.performStart();
}
case Fragment.STARTED:
if (newState > Fragment.STARTED) {
if (DEBUG) Log.v(TAG, "moveto RESUMED: " + f);
f.performResume();
f.mSavedFragmentState = null;
f.mSavedViewState = null;
}
}
} else if (f.mState > newState) {
switch (f.mState) {
case Fragment.RESUMED:
if (newState < Fragment.RESUMED) {
if (DEBUG) Log.v(TAG, "movefrom RESUMED: " + f);
f.performPause();
}
case Fragment.STARTED:
if (newState < Fragment.STARTED) {
if (DEBUG) Log.v(TAG, "movefrom STARTED: " + f);
f.performStop();
}
case Fragment.STOPPED:
if (newState < Fragment.STOPPED) {
if (DEBUG) Log.v(TAG, "movefrom STOPPED: " + f);
f.performReallyStop();
}
case Fragment.ACTIVITY_CREATED:
if (newState < Fragment.ACTIVITY_CREATED) {
if (DEBUG) Log.v(TAG, "movefrom ACTIVITY_CREATED: " + f);
if (f.mView != null) {
// Need to save the current view state if not
// done already.
if (mHost.onShouldSaveFragmentState(f) && f.mSavedViewState == null) {
saveFragmentViewState(f);
}
}
f.performDestroyView();
if (f.mView != null && f.mContainer != null) {
Animation anim = null;
if (mCurState > Fragment.INITIALIZING && !mDestroyed) {
anim = loadAnimation(f, transit, false,
transitionStyle);
}
if (anim != null) {
final Fragment fragment = f;
f.mAnimatingAway = f.mView;
f.mStateAfterAnimating = newState;
final View viewToAnimate = f.mView;
anim.setAnimationListener(new AnimateOnHWLayerIfNeededListener(
viewToAnimate, anim) {
@Override
public void onAnimationEnd(Animation animation) {
super.onAnimationEnd(animation);
if (fragment.mAnimatingAway != null) {
fragment.mAnimatingAway = null;
moveToState(fragment, fragment.mStateAfterAnimating,
0, 0, false);
}
}
});
f.mView.startAnimation(anim);
}
f.mContainer.removeView(f.mView);
}
f.mContainer = null;
f.mView = null;
f.mInnerView = null;
}
case Fragment.CREATED:
if (newState < Fragment.CREATED) {
if (mDestroyed) {
if (f.mAnimatingAway != null) {
// The fragment's containing activity is
// being destroyed, but this fragment is
// currently animating away. Stop the
// animation right now -- it is not needed,
// and we can't wait any more on destroying
// the fragment.
View v = f.mAnimatingAway;
f.mAnimatingAway = null;
v.clearAnimation();
}
}
if (f.mAnimatingAway != null) {
// We are waiting for the fragment's view to finish
// animating away. Just make a note of the state
// the fragment now should move to once the animation
// is done.
f.mStateAfterAnimating = newState;
newState = Fragment.CREATED;
} else {
if (DEBUG) Log.v(TAG, "movefrom CREATED: " + f);
if (!f.mRetaining) {
f.performDestroy();
} else {
f.mState = Fragment.INITIALIZING;
}
f.performDetach();
if (!keepActive) {
if (!f.mRetaining) {
makeInactive(f);
} else {
f.mHost = null;
f.mParentFragment = null;
f.mFragmentManager = null;
}
}
}
}
}
}
if (f.mState != newState) {
Log.w(TAG, "moveToState: Fragment state for " + f + " not updated inline; "
+ "expected state " + newState + " found " + f.mState);
f.mState = newState;
}
}frameworks/support/v4/java/android/support/v4/app/Fragment.java
final void restoreViewState(Bundle savedInstanceState) {
if (mSavedViewState != null) {
mInnerView.restoreHierarchyState(mSavedViewState);//Enter ViewGroup processing logic
mSavedViewState = null;
}
mCalled = false;
onViewStateRestored(savedInstanceState);
if (!mCalled) {
throw new SuperNotCalledException("Fragment " + this
+ " did not call through to super.onViewStateRestored()");
}
}frameworks/base/core/java/android/view/View.java
/**
* Restore this view hierarchy's frozen state from the given container.
*
* @param container The SparseArray which holds previously frozen states.
*
* @see #saveHierarchyState(android.util.SparseArray)
* @see #dispatchRestoreInstanceState(android.util.SparseArray)
* @see #onRestoreInstanceState(android.os.Parcelable)
*/
public void restoreHierarchyState(SparseArray<Parcelable> container) {
dispatchRestoreInstanceState(container);//Execute the processing logic of the derived class ViewGroup
}
frameworks/base/core/java/android/view/ViewGroup.java
@Override
protected void dispatchRestoreInstanceState(SparseArray<Parcelable> container) {
super.dispatchRestoreInstanceState(container);//Execute processing logic in parent View
final int count = mChildrenCount;
final View[] children = mChildren;
for (int i = 0; i < count; i++) {//Traversal SubView
View c = children[i];
if ((c.mViewFlags & PARENT_SAVE_DISABLED_MASK) != PARENT_SAVE_DISABLED) {
c.dispatchRestoreInstanceState(container);//Call the method in the subview.
}
}
}frameworks/base/core/java/android/view/View.java
/**
* Called by {@link #restoreHierarchyState(android.util.SparseArray)} to retrieve the
* state for this view and its children. May be overridden to modify how restoring
* happens to a view's children; for example, some views may want to not store state
* for their children.
*
* @param container The SparseArray which holds previously saved state.
*
* @see #dispatchSaveInstanceState(android.util.SparseArray)
* @see #restoreHierarchyState(android.util.SparseArray)
* @see #onRestoreInstanceState(android.os.Parcelable)
*/
protected void dispatchRestoreInstanceState(SparseArray<Parcelable> container) {
if (mID != NO_ID) {
Parcelable state = container.get(mID);// Based on the id of the current view, the status of the previously cached current view (that is, a Parcelable object) is extracted from the container.
if (state != null) {
// Log.i("View", "Restoreing #" + Integer.toHexString(mID)
// + ": " + state);
mPrivateFlags &= ~PFLAG_SAVE_STATE_CALLED; //Restore the initial value of mPrivateFlags
onRestoreInstanceState(state);//Call onRestoreInstanceState in View
if ((mPrivateFlags & PFLAG_SAVE_STATE_CALLED) == 0) {
throw new IllegalStateException(
"Derived class did not call super.onRestoreInstanceState()");
}
}
}
}OnRestore Instance State (Parcelable state) implementation:
Implementation of Android 7.0
/**
* Hook allowing a view to re-apply a representation of its internal state that had previously
* been generated by {@link #onSaveInstanceState}. This function will never be called with a
* null state.
*
* @param state The frozen state that had previously been returned by
* {@link #onSaveInstanceState}.
*
* @see #onSaveInstanceState()
* @see #restoreHierarchyState(android.util.SparseArray)
* @see #dispatchRestoreInstanceState(android.util.SparseArray)
*/
@CallSuper
protected void onRestoreInstanceState(Parcelable state) {
mPrivateFlags |= PFLAG_SAVE_STATE_CALLED;
if (state != null && !(state instanceof AbsSavedState)) {
throw new IllegalArgumentException("Wrong state class, expecting View State but "
+ "received " + state.getClass().toString() + " instead. This usually happens "
+ "when two views of different type have the same id in the same hierarchy. "
+ "This view's id is " + ViewDebug.resolveId(mContext, getId()) + ". Make sure "
+ "other views do not use the same id.");
}
if (state != null && state instanceof BaseSavedState) {
mStartActivityRequestWho = ((BaseSavedState) state).mStartActivityRequestWhoSaved;
}
}The implementation of android 4.4.4 is currently focused on version 4.0.
/**
* Hook allowing a view to re-apply a representation of its internal state that had previously
* been generated by {@link #onSaveInstanceState}. This function will never be called with a
* null state.
*
* @param state The frozen state that had previously been returned by
* {@link #onSaveInstanceState}.
*
* @see #onSaveInstanceState()
* @see #restoreHierarchyState(android.util.SparseArray)
* @see #dispatchRestoreInstanceState(android.util.SparseArray)
*/
protected void onRestoreInstanceState(Parcelable state) {
mPrivateFlags |= PFLAG_SAVE_STATE_CALLED;
if (state != BaseSavedState.EMPTY_STATE && state != null) { //anomaly detection
throw new IllegalArgumentException("Wrong state class, expecting View State but "
+ "received " + state.getClass().toString() + " instead. This usually happens "
+ "when two views of different type have the same id in the same hierarchy. "
+ "This view's id is " + ViewDebug.resolveId(mContext, getId()) + ". Make sure "
+ "other views do not use the same id.");
}
}0x06. summary
Restore the scene:
0x01. Uninhabited interface re-onStart();
0x02. Restore the state of view;
Parcelable state = container.get(mID); restore another View state (Parcelable object) of the unmanned customer service plug-in from memory before upgrading.
0x03. Triggered state!= BaseSavedState. EMPTY_STATE
Because the state value taken from the container based on the same View with the same id must be BaseSavedState.EMPTY_STATE, which results in an exception.
public static final AbsSavedState EMPTY_STATE = new AbsSavedState() {}; this is the true face of EMPTY_STATE, and the same view of the EMPTY_STATE object is bound to be the same.
0x04. From the perspective of plug-in's validity rules, it is impossible to reproduce the above problem. At present, it is impossible to reproduce the problem locally. At the same time, every upgraded plug-in user will only have such a crash once, so all doubts are just guesses.
View state's stored procedure is just the opposite of the above restore process, so here's just the last call, because it's related to EMPTY_STATE.
saveHierarchyState()
+------dispatchSaveInstanceState(SparseArray container)
+------onSaveInstanceState()View.java
/**
* Store this view hierarchy's frozen state into the given container.
*
* @param container The SparseArray in which to save the view's state.
*
* @see #restoreHierarchyState(android.util.SparseArray)
* @see #dispatchSaveInstanceState(android.util.SparseArray)
* @see #onSaveInstanceState()
*/
public void saveHierarchyState(SparseArray<Parcelable> container) {
dispatchSaveInstanceState(container);
}
/**
* Called by {@link #saveHierarchyState(android.util.SparseArray)} to store the state for
* this view and its children. May be overridden to modify how freezing happens to a
* view's children; for example, some views may want to not store state for their children.
*
* @param container The SparseArray in which to save the view's state.
*
* @see #dispatchRestoreInstanceState(android.util.SparseArray)
* @see #saveHierarchyState(android.util.SparseArray)
* @see #onSaveInstanceState()
*/
protected void dispatchSaveInstanceState(SparseArray<Parcelable> container) {
if (mID != NO_ID && (mViewFlags & SAVE_DISABLED_MASK) == 0) {
mPrivateFlags &= ~PFLAG_SAVE_STATE_CALLED;
Parcelable state = onSaveInstanceState();
if ((mPrivateFlags & PFLAG_SAVE_STATE_CALLED) == 0) {
throw new IllegalStateException(
"Derived class did not call super.onSaveInstanceState()");
}
if (state != null) {
// Log.i("View", "Freezing #" + Integer.toHexString(mID)
// + ": " + state);
container.put(mID, state);
}
}
}
/**
* Hook allowing a view to generate a representation of its internal state
* that can later be used to create a new instance with that same state.
* This state should only contain information that is not persistent or can
* not be reconstructed later. For example, you will never store your
* current position on screen because that will be computed again when a
* new instance of the view is placed in its view hierarchy.
* <p>
* Some examples of things you may store here: the current cursor position
* in a text view (but usually not the text itself since that is stored in a
* content provider or other persistent storage), the currently selected
* item in a list view.
*
* @return Returns a Parcelable object containing the view's current dynamic
* state, or null if there is nothing interesting to save. The
* default implementation returns null.
* @see #onRestoreInstanceState(android.os.Parcelable)
* @see #saveHierarchyState(android.util.SparseArray)
* @see #dispatchSaveInstanceState(android.util.SparseArray)
* @see #setSaveEnabled(boolean)
*/
@CallSuper
protected Parcelable onSaveInstanceState() {
mPrivateFlags |= PFLAG_SAVE_STATE_CALLED;
if (mStartActivityRequestWho != null) {
BaseSavedState state = new BaseSavedState(AbsSavedState.EMPTY_STATE);
state.mStartActivityRequestWhoSaved = mStartActivityRequestWho;
return state;
}
return BaseSavedState.EMPTY_STATE;
}Reference resources: