从做Android开发以来就一直被灌输“只能在主线程刷新UI”的思想，但是这两天发现个问题，在onCreate中创建工作线程并刷新UI没有报错。代码是这样的：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final TextView tv = (TextView) findViewById(R.id.sample_text);
new Thread(new Runnable() {
@Override
public void run() {
tv.setText("来自"+Thread.currentThread().getName()+"线程的更新");
}
}).start();
}
期待已久的crash没有出现，反而页面是这样显示的：
屏幕快照 2017-03-26 下午7.14.46.png
不禁让人陷入深思···
思考.jpg
第一步，分析问题原因。以前工作线程刷新UI会出现异常并提示只能在UI线程刷新UI。所以假设有个地方(函数)会在刷新UI前判断当前线程是不是主线程，那么现在问题就是验证下是否真的存在这么个地方。问题是从setText引起的，那就从这里出发看看。
点进去看下发现又调用了其重载函数：
@android.view.RemotableViewMethod
public final void setText(CharSequence text) {
setText(text, mBufferType);
}
继续深入发现这个方法代码挺多的，但是不用过于关注细节，粗略浏览下不难发现前面大部分代码大多是对text文本格式的一些处理判断，无关刷新UI，直到 checkForRelayout()方法执行，从名字看是“从新布局”，根据view绘制流程测量、布局、绘制，那布局完了不是就绘制刷新了吗？所以决定去checkForRelayout方法看看。
private void setText(CharSequence text, BufferType type,
boolean notifyBefore, int oldlen) {
if (text == null) {
text = "";
}
// If suggestions are not enabled, remove the suggestion spans from the text
if (!isSuggestionsEnabled()) {
text = removeSuggestionSpans(text);
}
if (!mUserSetTextScaleX) mTextPaint.setTextScaleX(1.0f);
if (text instanceof Spanned &&
((Spanned) text).getSpanStart(TextUtils.TruncateAt.MARQUEE) >= 0) {
if (ViewConfiguration.get(mContext).isFadingMarqueeEnabled()) {
setHorizontalFadingEdgeEnabled(true);
mMarqueeFadeMode = MARQUEE_FADE_NORMAL;
} else {
setHorizontalFadingEdgeEnabled(false);
mMarqueeFadeMode = MARQUEE_FADE_SWITCH_SHOW_ELLIPSIS;
}
setEllipsize(TextUtils.TruncateAt.MARQUEE);
}
int n = mFilters.length;
for (int i = 0; i < n; i++) {
CharSequence out = mFilters[i].filter(text, 0, text.length(), EMPTY_SPANNED, 0, 0);
if (out != null) {
text = out;
}
}
if (notifyBefore) {
if (mText != null) {
oldlen = mText.length();
sendBeforeTextChanged(mText, 0, oldlen, text.length());
} else {
sendBeforeTextChanged("", 0, 0, text.length());
}
}
boolean needEditableForNotification = false;
if (mListeners != null && mListeners.size() != 0) {
needEditableForNotification = true;
}
if (type == BufferType.EDITABLE || getKeyListener() != null ||
needEditableForNotification) {
createEditorIfNeeded();
Editable t = mEditableFactory.newEditable(text);
text = t;
setFilters(t, mFilters);
InputMethodManager imm = InputMethodManager.peekInstance();
if (imm != null) imm.restartInput(this);
} else if (type == BufferType.SPANNABLE || mMovement != null) {
text = mSpannableFactory.newSpannable(text);
} else if (!(text instanceof CharWrapper)) {
text = TextUtils.stringOrSpannedString(text);
}
if (mAutoLinkMask != 0) {
Spannable s2;
if (type == BufferType.EDITABLE || text instanceof Spannable) {
s2 = (Spannable) text;
} else {
s2 = mSpannableFactory.newSpannable(text);
}
if (Linkify.addLinks(s2, mAutoLinkMask)) {
text = s2;
type = (type == BufferType.EDITABLE) ? BufferType.EDITABLE : BufferType.SPANNABLE;
/*
* We must go ahead and set the text before changing the
* movement method, because setMovementMethod() may call
* setText() again to try to upgrade the buffer type.
*/
mText = text;
// Do not change the movement method for text that support text selection as it
// would prevent an arbitrary cursor displacement.
if (mLinksClickable && !textCanBeSelected()) {
setMovementMethod(LinkMovementMethod.getInstance());
}
}
}
mBufferType = type;
mText = text;
if (mTransformation == null) {
mTransformed = text;
} else {
mTransformed = mTransformation.getTransformation(text, this);
}
final int textLength = text.length();
if (text instanceof Spannable && !mAllowTransformationLengthChange) {
Spannable sp = (Spannable) text;
// Remove any ChangeWatchers that might have come from other TextViews.
final ChangeWatcher[] watchers = sp.getSpans(0, sp.length(), ChangeWatcher.class);
final int count = watchers.length;
for (int i = 0; i < count; i++) {
sp.removeSpan(watchers[i]);
}
if (mChangeWatcher == null) mChangeWatcher = new ChangeWatcher();
sp.setSpan(mChangeWatcher, 0, textLength, Spanned.SPAN_INCLUSIVE_INCLUSIVE |
(CHANGE_WATCHER_PRIORITY << Spanned.SPAN_PRIORITY_SHIFT));
if (mEditor != null) mEditor.addSpanWatchers(sp);
if (mTransformation != null) {
sp.setSpan(mTransformation, 0, textLength, Spanned.SPAN_INCLUSIVE_INCLUSIVE);
}
if (mMovement != null) {
mMovement.initialize(this, (Spannable) text);
/*
* Initializing the movement method will have set the
* selection, so reset mSelectionMoved to keep that from
* interfering with the normal on-focus selection-setting.
*/
if (mEditor != null) mEditor.mSelectionMoved = false;
}
}
if (mLayout != null) {
checkForRelayout();
}
sendOnTextChanged(text, 0, oldlen, textLength);
onTextChanged(text, 0, oldlen, textLength);
notifyViewAccessibilityStateChangedIfNeeded(AccessibilityEvent.CONTENT_CHANGE_TYPE_TEXT);
if (needEditableForNotification) {
sendAfterTextChanged((Editable) text);
}
// SelectionModifierCursorController depends on textCanBeSelected, which depends on text
if (mEditor != null) mEditor.prepareCursorControllers();
}
找到checkForRelayout方法查看：
private void checkForRelayout() {
// If we have a fixed width, we can just swap in a new text layout
// if the text height stays the same or if the view height is fixed.
if ((mLayoutParams.width != LayoutParams.WRAP_CONTENT ||
(mMaxWidthMode == mMinWidthMode && mMaxWidth == mMinWidth)) &&
(mHint == null || mHintLayout != null) &&
(mRight - mLeft - getCompoundPaddingLeft() - getCompoundPaddingRight() > 0)) {
// Static width, so try making a new text layout.
int oldht = mLayout.getHeight();
int want = mLayout.getWidth();
int hintWant = mHintLayout == null ? 0 : mHintLayout.getWidth();
/*
* No need to bring the text into view, since the size is not
* changing (unless we do the requestLayout(), in which case it
* will happen at measure).
*/
makeNewLayout(want, hintWant, UNKNOWN_BORING, UNKNOWN_BORING,
mRight - mLeft - getCompoundPaddingLeft() - getCompoundPaddingRight(),
false);
if (mEllipsize != TextUtils.TruncateAt.MARQUEE) {
// In a fixed-height view, so use our new text layout.
if (mLayoutParams.height != LayoutParams.WRAP_CONTENT &&
mLayoutParams.height != LayoutParams.MATCH_PARENT) {
invalidate();
return;
}
// Dynamic height, but height has stayed the same,
// so use our new text layout.
if (mLayout.getHeight() == oldht &&
(mHintLayout == null || mHintLayout.getHeight() == oldht)) {
invalidate();
return;
}
}
// We lose: the height has changed and we have a dynamic height.
// Request a new view layout using our new text layout.
requestLayout();
invalidate();
} else {
// Dynamic width, so we have no choice but to request a new
// view layout with a new text layout.
nullLayouts();
requestLayout();
invalidate();
}
}
发现不管是if还是else，都要执行invalidate()，那就进去看看，一路进展比较顺利，好像离真理更进一步了。经过连续的三连调跳转到了invalidateInternal方法：
public void invalidate() {
invalidate(true);
}
/**
* This is where the invalidate() work actually happens. A full invalidate()
* causes the drawing cache to be invalidated, but this function can be
* called with invalidateCache set to false to skip that invalidation step
* for cases that do not need it (for example, a component that remains at
* the same dimensions with the same content).
*
* @param invalidateCache Whether the drawing cache for this view should be
* invalidated as well. This is usually true for a full
* invalidate, but may be set to false if the View's contents or
* dimensions have not changed.
*/
void invalidate(boolean invalidateCache) {
invalidateInternal(0, 0, mRight - mLeft, mBottom - mTop, invalidateCache, true);
}
void invalidateInternal(int l, int t, int r, int b, boolean invalidateCache,
boolean fullInvalidate) {
if (mGhostView != null) {
mGhostView.invalidate(true);
return;
}
if (skipInvalidate()) {
return;
}
if ((mPrivateFlags & (PFLAG_DRAWN | PFLAG_HAS_BOUNDS)) == (PFLAG_DRAWN | PFLAG_HAS_BOUNDS)
|| (invalidateCache && (mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == PFLAG_DRAWING_CACHE_VALID)
|| (mPrivateFlags & PFLAG_INVALIDATED) != PFLAG_INVALIDATED
|| (fullInvalidate && isOpaque() != mLastIsOpaque)) {
if (fullInvalidate) {
mLastIsOpaque = isOpaque();
mPrivateFlags &= ~PFLAG_DRAWN;
}
mPrivateFlags |= PFLAG_DIRTY;
if (invalidateCache) {
mPrivateFlags |= PFLAG_INVALIDATED;
mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
}
// Propagate the damage rectangle to the parent view.
final AttachInfo ai = mAttachInfo;
final ViewParent p = mParent;
if (p != null && ai != null && l < r && t < b) {
final Rect damage = ai.mTmpInvalRect;
damage.set(l, t, r, b);
p.invalidateChild(this, damage);
}
// Damage the entire projection receiver, if necessary.
if (mBackground != null && mBackground.isProjected()) {
final View receiver = getProjectionReceiver();
if (receiver != null) {
receiver.damageInParent();
}
}
// Damage the entire IsolatedZVolume receiving this view's shadow.
if (isHardwareAccelerated() && getZ() != 0) {
damageShadowReceiver();
}
}
}
重点看invalidateChild()这个方法，方法里面有do while循环，每次循环出当前view的parent，最后一次循环返回的parent时ViewRootImpl类实例：
public final void invalidateChild(View child, final Rect dirty) {
ViewParent parent = this;
final AttachInfo attachInfo = mAttachInfo;
if (attachInfo != null) {
// If the child is drawing an animation, we want to copy this flag onto
// ourselves and the parent to make sure the invalidate request goes
// through
final boolean drawAnimation = (child.mPrivateFlags & PFLAG_DRAW_ANIMATION)
== PFLAG_DRAW_ANIMATION;
// Check whether the child that requests the invalidate is fully opaque
// Views being animated or transformed are not considered opaque because we may
// be invalidating their old position and need the parent to paint behind them.
Matrix childMatrix = child.getMatrix();
final boolean isOpaque = child.isOpaque() && !drawAnimation &&
child.getAnimation() == null && childMatrix.isIdentity();
// Mark the child as dirty, using the appropriate flag
// Make sure we do not set both flags at the same time
int opaqueFlag = isOpaque ? PFLAG_DIRTY_OPAQUE : PFLAG_DIRTY;
if (child.mLayerType != LAYER_TYPE_NONE) {
mPrivateFlags |= PFLAG_INVALIDATED;
mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
}
final int[] location = attachInfo.mInvalidateChildLocation;
location[CHILD_LEFT_INDEX] = child.mLeft;
location[CHILD_TOP_INDEX] = child.mTop;
if (!childMatrix.isIdentity() ||
(mGroupFlags & ViewGroup.FLAG_SUPPORT_STATIC_TRANSFORMATIONS) != 0) {
RectF boundingRect = attachInfo.mTmpTransformRect;
boundingRect.set(dirty);
Matrix transformMatrix;
if ((mGroupFlags & ViewGroup.FLAG_SUPPORT_STATIC_TRANSFORMATIONS) != 0) {
Transformation t = attachInfo.mTmpTransformation;
boolean transformed = getChildStaticTransformation(child, t);
if (transformed) {
transformMatrix = attachInfo.mTmpMatrix;
transformMatrix.set(t.getMatrix());
if (!childMatrix.isIdentity()) {
transformMatrix.preConcat(childMatrix);
}
} else {
transformMatrix = childMatrix;
}
} else {
transformMatrix = childMatrix;
}
transformMatrix.mapRect(boundingRect);
dirty.set((int) (boundingRect.left - 0.5f),
(int) (boundingRect.top - 0.5f),
(int) (boundingRect.right + 0.5f),
(int) (boundingRect.bottom + 0.5f));
}
do {
View view = null;
if (parent instanceof View) {
view = (View) parent;
}
if (drawAnimation) {
if (view != null) {
view.mPrivateFlags |= PFLAG_DRAW_ANIMATION;
} else if (parent instanceof ViewRootImpl) {
((ViewRootImpl) parent).mIsAnimating = true;
}
}
// If the parent is dirty opaque or not dirty, mark it dirty with the opaque
// flag coming from the child that initiated the invalidate
if (view != null) {
if ((view.mViewFlags & FADING_EDGE_MASK) != 0 &&
view.getSolidColor() == 0) {
opaqueFlag = PFLAG_DIRTY;
}
if ((view.mPrivateFlags & PFLAG_DIRTY_MASK) != PFLAG_DIRTY) {
view.mPrivateFlags = (view.mPrivateFlags & ~PFLAG_DIRTY_MASK) | opaqueFlag;
}
}
parent = parent.invalidateChildInParent(location, dirty);
if (view != null) {
// Account for transform on current parent
Matrix m = view.getMatrix();
if (!m.isIdentity()) {
RectF boundingRect = attachInfo.mTmpTransformRect;
boundingRect.set(dirty);
m.mapRect(boundingRect);
dirty.set((int) (boundingRect.left - 0.5f),
(int) (boundingRect.top - 0.5f),
(int) (boundingRect.right + 0.5f),
(int) (boundingRect.bottom + 0.5f));
}
}
} while (parent != null);
}
}
现在查看ViewRootImpl类的invalidateChildInParent()方法：
@Override
public ViewParent invalidateChildInParent(int[] location, Rect dirty) {
checkThread();
if (DEBUG_DRAW) Log.v(TAG, "Invalidate child: " + dirty);
if (dirty == null) {
invalidate();
return null;
} else if (dirty.isEmpty() && !mIsAnimating) {
return null;
}
if (mCurScrollY != 0 || mTranslator != null) {
mTempRect.set(dirty);
dirty = mTempRect;
if (mCurScrollY != 0) {
dirty.offset(0, -mCurScrollY);
}
if (mTranslator != null) {
mTranslator.translateRectInAppWindowToScreen(dirty);
}
if (mAttachInfo.mScalingRequired) {
dirty.inset(-1, -1);
}
}
final Rect localDirty = mDirty;
if (!localDirty.isEmpty() && !localDirty.contains(dirty)) {
mAttachInfo.mSetIgnoreDirtyState = true;
mAttachInfo.mIgnoreDirtyState = true;
}
// Add the new dirty rect to the current one
localDirty.union(dirty.left, dirty.top, dirty.right, dirty.bottom);
// Intersect with the bounds of the window to skip
// updates that lie outside of the visible region
final float appScale = mAttachInfo.mApplicationScale;
final boolean intersected = localDirty.intersect(0, 0,
(int) (mWidth * appScale + 0.5f), (int) (mHeight * appScale + 0.5f));
if (!intersected) {
localDirty.setEmpty();
}
if (!mWillDrawSoon && (intersected || mIsAnimating)) {
scheduleTraversals();
}
return null;
}
方法块的第一行好像就是我们要找的验证线程的地方checkThread()，而该方法内容也很简单，看到抛出的异常就很熟悉了：
void checkThread() {
if (mThread != Thread.currentThread()) {
throw new CalledFromWrongThreadException(
"Only the original thread that created a view hierarchy can touch its views.");
}
}
第二步，验证线程地方已经找到了，假设得到了证实，那么为什么该有的异常没有出现呢？现在再次假设是不是因为某些原因导致checkThread()没有执行呢？
有人可能会问会不会是mThread == Thread.currentThread()？其实这是不可能的 ，先看下mThread赋值：
public ViewRootImpl(Context context, Display display) {
mContext = context;
mWindowSession = WindowManagerGlobal.getWindowSession();
mDisplay = display;
mBasePackageName = context.getBasePackageName();
mDisplayAdjustments = display.getDisplayAdjustments();
mThread = Thread.currentThread();
ViewRootImpl类实例化是在Activity启动时的主线程创建的，所以mThread是主线程实例，而checkThread()中的Thread.currentThread()，最初是由textView.setText()调用的一系列方法栈，并且setText是在子线程调用。
继续刚才的假设，不过现在要逆推回去，checkThread()方法没有执行，可以认为ViewRootImpl的invalidateChildInParent()方法没有执行，它又是在ViewGroup中invalidateChild()方法里的do while中调用，要使do while不被调用，继续往上看，如果attachInfo为null，进不去if语句块也就不会执行checkThread()了，这是第一个可能的原因。记录下，继续逆推。
View中的invalidateInternal()方法：
// Propagate the damage rectangle to the parent view.
final AttachInfo ai = mAttachInfo;
final ViewParent p = mParent;
if (p != null && ai != null && l < r && t < b) {
final Rect damage = ai.mTmpInvalRect;
damage.set(l, t, r, b);
p.invalidateChild(this, damage);
}
根据判断条件，如果p即mParent或者ai即mAttachInfo 任一为null，都不会执行invalidateChild，这是第二个可能原因，这里的ai和第一个原因的attachInfo是一样的，所以第一个原因可能忽略，精力关注在第二个原因上。
现在的关注点是实例p和ai是什么时候创建的，有没有为null的现象？
final AttachInfo ai = mAttachInfo;
而mAttachInfo是在View的dispatchAttachedToWindow()方法中赋值的：
void dispatchAttachedToWindow(AttachInfo info, int visibility) {
//System.out.println("Attached! " + this);
mAttachInfo = info;
}
View的dispatchAttachedToWindow()方法是在ViewRootImpl中的performTraversals()方法调用，这个方法是遍历View Tree，
private void performTraversals() {
// cache mView since it is used so much below...
final View host = mView;
·······
host.dispatchAttachedToWindow(mAttachInfo, 0);
可见View中的mAttachInfo来自ViewrootImpl的mAttachInfo，而ViewrootImpl的mAttachInfo是在其构造方法中被赋值的：
public ViewRootImpl(Context context, Display display) {
mContext = context;
mWindowSession = WindowManagerGlobal.getWindowSession();
mDisplay = display;
mBasePackageName = context.getBasePackageName();
mDisplayAdjustments = display.getDisplayAdjustments();
mThread = Thread.currentThread();
mLocation = new WindowLeaked(null);
mLocation.fillInStackTrace();
mWidth = -1;
mHeight = -1;
mDirty = new Rect();
mTempRect = new Rect();
mVisRect = new Rect();
mWinFrame = new Rect();
mWindow = new W(this);
mTargetSdkVersion = context.getApplicationInfo().targetSdkVersion;
mViewVisibility = View.GONE;
mTransparentRegion = new Region();
mPreviousTransparentRegion = new Region();
mFirst = true; // true for the first time the view is added
mAdded = false;
mAttachInfo = new View.AttachInfo(mWindowSession, mWindow, display, this, mHandler, this);
}
之前说了ViewRootImpl实例是在Activity启动时创建的，现在看看具体是启动的什么时候:在向window添加view的时候即：WindowManagerGlobal的addView方法中创建ViewrootImpl实例：
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow) {
if (view == null) {
throw new IllegalArgumentException("view must not be null");
}
if (display == null) {
throw new IllegalArgumentException("display must not be null");
}
if (!(params instanceof WindowManager.LayoutParams)) {
throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
}
final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;
if (parentWindow != null) {
parentWindow.adjustLayoutParamsForSubWindow(wparams);
} else {
// If there's no parent and we're running on L or above (or in the
// system context), assume we want hardware acceleration.
final Context context = view.getContext();
if (context != null
&& context.getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.LOLLIPOP) {
wparams.flags |= WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
}
}
ViewRootImpl root;
View panelParentView = null;
synchronized (mLock) {
// Start watching for system property changes.
if (mSystemPropertyUpdater == null) {
mSystemPropertyUpdater = new Runnable() {
@Override public void run() {
synchronized (mLock) {
for (int i = mRoots.size() - 1; i >= 0; --i) {
mRoots.get(i).loadSystemProperties();
}
}
}
};
SystemProperties.addChangeCallback(mSystemPropertyUpdater);
}
int index = findViewLocked(view, false);
if (index >= 0) {
if (mDyingViews.contains(view)) {
// Don't wait for MSG_DIE to make it's way through root's queue.
mRoots.get(index).doDie();
} else {
throw new IllegalStateException("View " + view
+ " has already been added to the window manager.");
}
// The previous removeView() had not completed executing. Now it has.
}
// If this is a panel window, then find the window it is being
// attached to for future reference.
if (wparams.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW &&
wparams.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) {
final int count = mViews.size();
for (int i = 0; i < count; i++) {
if (mRoots.get(i).mWindow.asBinder() == wparams.token) {
panelParentView = mViews.get(i);
}
}
}
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
mViews.add(view);
mRoots.add(root);
mParams.add(wparams);
}
// do this last because it fires off messages to start doing things
try {
root.setView(view, wparams, panelParentView);
} catch (RuntimeException e) {
// BadTokenException or InvalidDisplayException, clean up.
synchronized (mLock) {
final int index = findViewLocked(view, false);
if (index >= 0) {
removeViewLocked(index, true);
}
}
throw e;
}
}
而调用addView()方法是在ActivityThread类的handleResumeActivity()方法：
final void handleResumeActivity(IBinder token,
boolean clearHide, boolean isForward, boolean reallyResume) {
// If we are getting ready to gc after going to the background, well
// we are back active so skip it.
unscheduleGcIdler();
mSomeActivitiesChanged = true;
// TODO Push resumeArgs into the activity for consideration
ActivityClientRecord r = performResumeActivity(token, clearHide);
if (r != null) {
final Activity a = r.activity;
if (localLOGV) Slog.v(
TAG, "Resume " + r + " started activity: " +
a.mStartedActivity + ", hideForNow: " + r.hideForNow
+ ", finished: " + a.mFinished);
final int forwardBit = isForward ?
WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION : 0;
// If the window hasn't yet been added to the window manager,
// and this guy didn't finish itself or start another activity,
// then go ahead and add the window.
boolean willBeVisible = !a.mStartedActivity;
if (!willBeVisible) {
try {
willBeVisible = ActivityManagerNative.getDefault().willActivityBeVisible(
a.getActivityToken());
} catch (RemoteException e) {
}
}
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
l.softInputMode |= forwardBit;
if (a.mVisibleFromClient) {
a.mWindowAdded = true;
wm.addView(decor, l);
}
// If the window has already been added, but during resume
// we started another activity, then don't yet make the
// window visible.
} else if (!willBeVisible) {
if (localLOGV) Slog.v(
TAG, "Launch " + r + " mStartedActivity set");
r.hideForNow = true;
}
// Get rid of anything left hanging around.
cleanUpPendingRemoveWindows(r);
// The window is now visible if it has been added, we are not
// simply finishing, and we are not starting another activity.
if (!r.activity.mFinished && willBeVisible
&& r.activity.mDecor != null && !r.hideForNow) {
if (r.newConfig != null) {
if (DEBUG_CONFIGURATION) Slog.v(TAG, "Resuming activity "
+ r.activityInfo.name + " with newConfig " + r.newConfig);
performConfigurationChanged(r.activity, r.newConfig);
freeTextLayoutCachesIfNeeded(r.activity.mCurrentConfig.diff(r.newConfig));
r.newConfig = null;
}
if (localLOGV) Slog.v(TAG, "Resuming " + r + " with isForward="
+ isForward);
WindowManager.LayoutParams l = r.window.getAttributes();
if ((l.softInputMode
& WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION)
!= forwardBit) {
l.softInputMode = (l.softInputMode
& (~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION))
| forwardBit;
if (r.activity.mVisibleFromClient) {
ViewManager wm = a.getWindowManager();
View decor = r.window.getDecorView();
wm.updateViewLayout(decor, l);
}
}
r.activity.mVisibleFromServer = true;
mNumVisibleActivities++;
if (r.activity.mVisibleFromClient) {
r.activity.makeVisible();
}
}
if (!r.onlyLocalRequest) {
r.nextIdle = mNewActivities;
mNewActivities = r;
if (localLOGV) Slog.v(
TAG, "Scheduling idle handler for " + r);
Looper.myQueue().addIdleHandler(new Idler());
}
r.onlyLocalRequest = false;
// Tell the activity manager we have resumed.
if (reallyResume) {
try {
ActivityManagerNative.getDefault().activityResumed(token);
} catch (RemoteException ex) {
}
}
} else {
// If an exception was thrown when trying to resume, then
// just end this activity.
try {
ActivityManagerNative.getDefault()
.finishActivity(token, Activity.RESULT_CANCELED, null, false);
} catch (RemoteException ex) {
}
}
}
看到上面的方法有些人心里可能有底儿了，handleResumeActivity()方法是不是让Activity回调onResume？如果是的话一切就都明了了，因为ViewrootImpl是在onReume期间创建，而AttachInfo是在ViewRootImpl实例化时创建，我们的工作线程是在onCreate时刷新UI的，那时候还没有实例化AttachInfo，导致mAttachInfo为null，最终if条件判断失败没有进入。然而这一切都是在YY，实践才是检验真理的唯一标准，动起来：
看到这一行代码```
ActivityClientRecord r = performResumeActivity(token, clearHide);
public final ActivityClientRecord performResumeActivity(IBinder token,
boolean clearHide) {
ActivityClientRecord r = mActivities.get(token);
if (localLOGV) Slog.v(TAG, "Performing resume of " + r
+ " finished=" + r.activity.mFinished);
if (r != null && !r.activity.mFinished) {
if (clearHide) {
r.hideForNow = false;
r.activity.mStartedActivity = false;
}
try {
r.activity.mFragments.noteStateNotSaved();
if (r.pendingIntents != null) {
deliverNewIntents(r, r.pendingIntents);
r.pendingIntents = null;
}
if (r.pendingResults != null) {
deliverResults(r, r.pendingResults);
r.pendingResults = null;
}
r.activity.performResume();
EventLog.writeEvent(LOG_ON_RESUME_CALLED,
UserHandle.myUserId(), r.activity.getComponentName().getClassName());
r.paused = false;
r.stopped = false;
r.state = null;
r.persistentState = null;
} catch (Exception e) {
if (!mInstrumentation.onException(r.activity, e)) {
throw new RuntimeException(
"Unable to resume activity "
+ r.intent.getComponent().toShortString()
+ ": " + e.toString(), e);
}
}
}
return r;
}
代码很短，很容易提取有用信息：``` r.activity.performResume();```在进去看看：
final void performResume() {
performRestart();
mFragments.execPendingActions();
mLastNonConfigurationInstances = null;
mCalled = false;
// mResumed is set by the instrumentation
mInstrumentation.callActivityOnResume(this);
if (!mCalled) {
throw new SuperNotCalledException(
"Activity " + mComponent.toShortString() +
" did not call through to super.onResume()");
}
// Now really resume, and install the current status bar and menu.
mCalled = false;
mFragments.dispatchResume();
mFragments.execPendingActions();
onPostResume();
if (!mCalled) {
throw new SuperNotCalledException(
"Activity " + mComponent.toShortString() +
" did not call through to super.onPostResume()");
}
}
看到```mInstrumentation```这个属性就能感觉到越来越接近SDK API层了，看看它的```callActivityOnResume()```方法做了什么：
public void callActivityOnResume(Activity activity) {
activity.mResumed = true;
activity.onResume();
if (mActivityMonitors != null) {
synchronized (mSync) {
final int N = mActivityMonitors.size();
for (int i=0; i<N; i++) {
final ActivityMonitor am = mActivityMonitors.get(i);
am.match(activity, activity, activity.getIntent());
}
}
}
}
一行```activity.onResume();```已经水落石出。
回到handleResumeActivity代码中，我精简下：
final void handleResumeActivity(IBinder token,
boolean clearHide, boolean isForward, boolean reallyResume) {
//这里是最终回调Activity的onResume()方法
ActivityClientRecord r = performResumeActivity(token, clearHide);
//省略若干
if (r != null) {
final Activity a = r.activity;
final int forwardBit = isForward ?
WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION : 0;
boolean willBeVisible = !a.mStartedActivity;
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
l.softInputMode |= forwardBit;
if (a.mVisibleFromClient) {
a.mWindowAdded = true;
//这里是调用WindowManagerGlobal的addView()方法最终实例化ViewRootImpl，进而实例化AttachInfo
wm.addView(decor, l);
}
} else if (!willBeVisible) {
if (localLOGV) Slog.v(
TAG, "Launch " + r + " mStartedActivity set");
r.hideForNow = true;
}
}
}
另外关于阅读源码问题，win下当然使用SourceInsight不二选，如果是在mac下可以参考我的[osx下如何使用SublimeText阅读Android系统源码](http://www.jianshu.com/p/c295d2729ecf).。
