Activity在onResume方法之后开始进行绘制(measure,layout,draw)setContentView中的内容。在measure之前是没有获取到控件的大小的。
绘制过程
在上一篇中，走了一边Activity启动过程，在这里，继续分析下视图的加载过程。
在调用了onStart 和 onResume方法之后，通过Activity中的PhoneWindow(Window)获取到WindowManager，将PhoneWindow中的DectorView添加到WindowManager中。
final void handleResumeActivity(IBinder token, boolean clearHide, boolean isForward, boolean reallyResume) {
unscheduleGcIdler();
mSomeActivitiesChanged = true;
// 调用 onStart 和 onResume方法
ActivityClientRecord r = performResumeActivity(token, clearHide);
if (r != null) {
final Activity a = r.activity;
// 开始将decor添加到WindowManager之中
// view的绘制流程开始
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); // 对ViewRootImpl 进行了初始化
}
}
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);// 到底怎么搞的
}
}
}
}
mWindowManager是在Window中创建，是一个WindowManagerImpl实例。那么.addView的方法，调用的也是WindowManagerImpl的方法。
public void setWindowManager(WindowManager wm, IBinder appToken, String appName, boolean hardwareAccelerated) {
mAppToken = appToken;
mAppName = appName;
mHardwareAccelerated = hardwareAccelerated
|| SystemProperties.getBoolean(PROPERTY_HARDWARE_UI, false);
if (wm == null) {
wm = (WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE);
}
mWindowManager = ((WindowManagerImpl)wm).createLocalWindowManager(this);
}
WindowManagerImpl中的.addView方法调用的是mGlobal的.addView的方法。在mGlobal的方法中对ViewRootImpl进行了初始化，ViewRootImpl实现了ViewParent接口。至此添加View完毕，接下来看看如何进行的绘制。
@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.addView(view, params, mDisplay, mParentWindow);
}
public void addView(View view, ViewGroup.LayoutParams params, Display display, Window parentWindow) {
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
mViews.add(view);
mRoots.add(root);
mParams.add(wparams);
}
}
ViewRootImpl在这里起到了一个与decorView链接的作用
返回到handleResumeActivity中，添加了之后，调用了WindowManagerImpl的updateViewLayout方法。
@Override
public void updateViewLayout(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.updateViewLayout(view, params);
}
在该方法中，根据mView的index，获取到对应的ViewRootImpl。这一步的初始化在上面的addview的时候进行了添加。然后调用ViewRootImpl的setLayoutParams方法。
public void updateViewLayout(View view, ViewGroup.LayoutParams params) {
synchronized (mLock) {
int index = findViewLocked(view, true);
ViewRootImpl root = mRoots.get(index);
mParams.remove(index);
mParams.add(index, wparams);
root.setLayoutParams(wparams, false);
}
}
void setLayoutParams(WindowManager.LayoutParams attrs, boolean newView) {
synchronized (this) {
if (newView) {
requestLayout();
}
}
}
在这里进行了线程的检查，mThread在创建ViewRootImpl时候，就被指定，所以，在这之后更新UI都是要报错的。
@Override
public void requestLayout() {
if (!mHandlingLayoutInLayoutRequest) {
checkThread();
mLayoutRequested = true;
scheduleTraversals();
}
}
void scheduleTraversals() {
if (!mTraversalScheduled) {
mChoreographer.postCallback(Choreographer.CALLBACK_TRAVERSAL,
// 执行 mTraversalRunnable 中的 run 方法
mTraversalRunnable, null);
if (!mUnbufferedInputDispatch) {
scheduleConsumeBatchedInput();
}
notifyRendererOfFramePending();
pokeDrawLockIfNeeded();
}
}
final class TraversalRunnable implements Runnable {
@Override
public void run() {
doTraversal();
}
}
void doTraversal() {
if (mTraversalScheduled) {
performTraversals();
}
}
在这个方法里，调用么测量，布局和绘制。
private void performTraversals() {
// cache mView since it is used so much below...
// mView 是 DectorView
final View host = mView;
if (!mStopped || mReportNextDraw) {
boolean focusChangedDueToTouchMode = ensureTouchModeLocally( (relayoutResult&WindowManagerGlobal.RELAYOUT_RES_IN_TOUCH_MODE) != 0);
if (focusChangedDueToTouchMode || mWidth != host.getMeasuredWidth()|| mHeight != host.getMeasuredHeight() || contentInsetsChanged) {
int childWidthMeasureSpec = getRootMeasureSpec(mWidth, lp.width);
int childHeightMeasureSpec = getRootMeasureSpec(mHeight, lp.height);
// 测量
// Ask host how big it wants to be
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
layoutRequested = true;
}
}
} else {
}
final boolean didLayout = layoutRequested && (!mStopped || mReportNextDraw);
boolean triggerGlobalLayoutListener = didLayout
|| mAttachInfo.mRecomputeGlobalAttributes;
if (didLayout) {
// 布局
performLayout(lp, desiredWindowWidth, desiredWindowHeight);
}
if (!cancelDraw && !newSurface) {
if (!skipDraw || mReportNextDraw) {
// 绘制
performDraw();
}
} else {
}
mIsInTraversal = false;
}
测量是调用的View的measure方法。
private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "measure");
try {
mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}
可以看到在这里调用了onMeasure方法，那么mView是DecorView，DecorView继承FrameLayout。Frame Layout重写了该方法。
public final void measure(int widthMeasureSpec, int heightMeasureSpec) {
if ((mPrivateFlags & PFLAG_FORCE_LAYOUT) == PFLAG_FORCE_LAYOUT || widthMeasureSpec != mOldWidthMeasureSpec || heightMeasureSpec != mOldHeightMeasureSpec) {
int cacheIndex = (mPrivateFlags & PFLAG_FORCE_LAYOUT) == PFLAG_FORCE_LAYOUT ? -1 : mMeasureCache.indexOfKey(key);
if (cacheIndex < 0 || sIgnoreMeasureCache) {
onMeasure(widthMeasureSpec, heightMeasureSpec);
}
}
}
这里是FrameLayout的onMeasure，其他的布局也会根据自己情况来复写该方法。在该方法中，获取到所有的子View，调用子View的child.measure方法。
/**
* {@inheritDoc}
* 如果，子 view如果设置属性是 match_parent，
* 如果，measureMatchParentChildren是true (其实就是framlayout模式是非精准模式)
* 那么这种子view是被测量了两次
*/
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int count = getChildCount();
//当FrameLayout的宽和高 只有同时设置为 match_parent
//当FrameLayout的宽和高 指定的size
///measureMatchParentChlidren = false，否则为true。
//MeasureSpec.EXACTLY时，就表示当前视图的大小等于参数measureSpec中所指定的值。
//当FrameLayout 非精准模式，这时候要把所有宽高设置为 //match_parent的子View都记录下来
// 这时候FrameLayout的宽高同时受子View的影响
final boolean measureMatchParentChildren = MeasureSpec.getMode(widthMeasureSpec) != MeasureSpec.EXACTLY || MeasureSpec.getMode(heightMeasureSpec) != MeasureSpec.EXACTLY;
mMatchParentChildren.clear();
int maxHeight = 0;
int maxWidth = 0;
int childState = 0;//宽高的期望类型
//测量孩子同时，计算出一个最大宽高
for (int i = 0; i < count; i++) {
final View child = getChildAt(i);
if (mMeasureAllChildren || child.getVisibility() != GONE) { //一次遍历每一个不为GONE的子view
//第一次测量孩子
measureChildWithMargins(child, widthMeasureSpec, 0, heightMeasureSpec, 0);
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
maxWidth = Math.max(maxWidth, child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin);
maxHeight = Math.max(maxHeight, child.getMeasuredHeight() + lp.topMargin + lp.bottomMargin);
childState = combineMeasuredStates(childState, child.getMeasuredState());
//的mMatchParentChlidren的list里存的是设置为match_parent的子view。
if (measureMatchParentChildren) {
if (lp.width == LayoutParams.MATCH_PARENT || lp.height == LayoutParams.MATCH_PARENT) {
mMatchParentChildren.add(child);
}
}
}
}
// Account for padding too
//加上父亲的padidng
maxWidth += getPaddingLeftWithForeground() + getPaddingRightWithForeground();
maxHeight += getPaddingTopWithForeground() + getPaddingBottomWithForeground();
// Check against our minimum height and width
// 校验最小宽高
maxHeight = Math.max(maxHeight, getSuggestedMinimumHeight());
maxWidth = Math.max(maxWidth, getSuggestedMinimumWidth());
// 与前景图片比较，获取宽高相对较大的值
final Drawable drawable = getForeground();
if (drawable != null) {
maxHeight = Math.max(maxHeight, drawable.getMinimumHeight());
maxWidth = Math.max(maxWidth, drawable.getMinimumWidth());
}
//设置测量过的宽高
setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, childState),
resolveSizeAndState(maxHeight, heightMeasureSpec,
childState << MEASURED_HEIGHT_STATE_SHIFT));
//上面的测量，得到了framlayout的宽，高，下面，需要根据宽高，重新测量子view - 主要是 match_parent 属性的孩子
//子view中设定为match_parent的个数
//重新测量
count = mMatchParentChildren.size();
if (count > 1) {
for (int i = 0; i < count; i++) {
final View child = mMatchParentChildren.get(i);
final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
final int childWidthMeasureSpec;
//将属性为match_parent的再测量一遍
if (lp.width == LayoutParams.MATCH_PARENT) {//子view的宽是match_parent，则宽度期望值是总宽度-padding-margin
final int width = Math.max(0, getMeasuredWidth()
- getPaddingLeftWithForeground() - getPaddingRightWithForeground()
- lp.leftMargin - lp.rightMargin);
childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(
width, MeasureSpec.EXACTLY);
} else {
childWidthMeasureSpec = getChildMeasureSpec(widthMeasureSpec,
getPaddingLeftWithForeground() + getPaddingRightWithForeground() +
lp.leftMargin + lp.rightMargin,
lp.width);
}
//将属性为match_parent的再测量一遍
final int childHeightMeasureSpec;
if (lp.height == LayoutParams.MATCH_PARENT) {
final int height = Math.max(0, getMeasuredHeight()
- getPaddingTopWithForeground() - getPaddingBottomWithForeground()
- lp.topMargin - lp.bottomMargin);
childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(
height, MeasureSpec.EXACTLY);
} else {
childHeightMeasureSpec = getChildMeasureSpec(heightMeasureSpec,
getPaddingTopWithForeground() + getPaddingBottomWithForeground() +
lp.topMargin + lp.bottomMargin,
lp.height);
}
//子view的宽是match_parent，则宽度期望值是总宽度-padding-margin
//把这部分子view重新计算大小
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}
}
}
private void performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth, int desiredWindowHeight) {
mLayoutRequested = false;
mScrollMayChange = true;
mInLayout = true;
final View host = mView;
try {
host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());
}
}
View和ViewGroup的事件分发
View事件分发
View只有事件的分发和消费。
从View的dispatchTouchEvent（事件分发）开始，在ListenerInfo中存放了所有得listener的信息，构建得了一个对象。
这句话是非常重点。 if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED && li.mOnTouchListener.onTouch(this, event))
如果View的.setOnTouchListener有对象的时候，先执行mOnTouchListener，如果消费了(返回True)，则不在执行View的onTouchEvent。
如果mOnTouchListener返回false，在会执行View的onTouchEvent方法。
如果mOnTouchListener返回false, 如果复写了View的onTouchEvent方法，确没有调用super，则不会执行到点击事件。
public boolean dispatchTouchEvent(MotionEvent event) {
boolean result = false;
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
stopNestedScroll();
}
if (onFilterTouchEventForSecurity(event)) {
//noinspection SimplifiableIfStatement
// 关键 -- 放了什么东西, 里面很多得参数
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
// enable 是否为true
&& (mViewFlags & ENABLED_MASK) == ENABLED
// 当onTouchListener 设置后是否为false
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
if (!result && onTouchEvent(event)) {
result = true;
}
if (actionMasked == MotionEvent.ACTION_UP ||
actionMasked == MotionEvent.ACTION_CANCEL ||
(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
stopNestedScroll();
}
return result;
}
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
if (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
switch (action) {
case MotionEvent.ACTION_UP:
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
boolean focusTaken = false;
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
if (!focusTaken) {
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {
// 点击事件
performClick();
}
}
}
}
mIgnoreNextUpEvent = false;
break;
}
return true;
}
return false;
}
ViewGroup事件分发
ViewGroup有事件的分发，拦截，消费。 先调用了本类中的拦截方法onInterceptTouchEvent，默认是返回false，如果没有拦截复写返回true，也没有取消该事件那么会倒序的循环所有的children。这也是为FrameLayout和RelativeLayout这种重叠的布局考虑，在dispatchTransformedTouchEvent方法中调用了child.dispatchTouchEvent(event)。在为mFirstTouchTarget进行赋值。否则mFirstTouchTarget为null。
如果child是View那么会执行上面View分发的流程。 如果child是viewGroup则会又开始执行本流程。 如果有子View进行了消费，那么break循环，返回true。
如果左右的子View没有消费该down事件，那么mFirstTouchTarget则为null，为null会调用super.dispatchTouchEvent然后自己消费该事件。
public boolean dispatchTouchEvent(MotionEvent ev) {
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// 很重要的一个地方了
if (actionMasked == MotionEvent.ACTION_DOWN) {
// 做了一次清除TouchState mFirstTouchTarget成了空
cancelAndClearTouchTargets(ev);
resetTouchState();
}
// Check for interception.
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
// down 事件的情况下 ，会调用该行,调用拦截的方法，
intercepted = onInterceptTouchEvent(ev); // 默认返回false，需要看子类
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false;
}
} else {
intercepted = true;
}
if (intercepted || mFirstTouchTarget != null) {
ev.setTargetAccessibilityFocus(false);
}
// Check for cancelation.
final boolean canceled = resetCancelNextUpFlag(this) || actionMasked == MotionEvent.ACTION_CANCEL;
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
//没拦截 并且 没取消，，默认情况下为true ，if语句 可以执行
if (!canceled && !intercepted) {
View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus() ? findChildWithAccessibilityFocus() : null;
if (actionMasked == MotionEvent.ACTION_DOWN || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN) || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
final int actionIndex = ev.getActionIndex(); // always 0 for down
final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex) : TouchTarget.ALL_POINTER_IDS;
removePointersFromTouchTargets(idBitsToAssign);
// 执行到这里 down的时候
final int childrenCount = mChildrenCount;
if (newTouchTarget == null && childrenCount != 0) {
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
// Find a child that can receive the event.
// Scan children from front to back.
final ArrayList<View> preorderedList = buildOrderedChildList();
final boolean customOrder = preorderedList == null && isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
// 反序 for 循环 ，fragmentlayou的话从顶层开始i
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = customOrder ? getChildDrawingOrder(childrenCount, i) : i;
final View child = (preorderedList == null) ? children[childIndex] : preorderedList.get(childIndex);
if (childWithAccessibilityFocus != null) {
if (childWithAccessibilityFocus != child) {
continue;
}
childWithAccessibilityFocus = null;
i = childrenCount - 1;
}
if (!canViewReceivePointerEvents(child) || !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
// 11
newTouchTarget = getTouchTarget(child); // 获取view的target
if (newTouchTarget != null) {
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUpFlag(child);
// 调用子view的dispatchTouchEvent
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
if (preorderedList != null) {
// childIndex points into presorted list, find original index
for (int j = 0; j < childrenCount; j++) {
if (children[childIndex] == mChildren[j]) {
mLastTouchDownIndex = j;
break;
}
}
} else {
mLastTouchDownIndex = childIndex;
}
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
ev.setTargetAccessibilityFocus(false);
}
if (preorderedList != null) preorderedList.clear();
}
if (newTouchTarget == null && mFirstTouchTarget != null) {
// Did not find a child to receive the event.
// Assign the pointer to the least recently added target.
newTouchTarget = mFirstTouchTarget;
while (newTouchTarget.next != null) {
newTouchTarget = newTouchTarget.next;
}
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
}
}
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
handled = dispatchTransformedTouchEvent(ev, canceled, null, TouchTarget.ALL_POINTER_IDS);
} else {
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child) || intercepted;
if (dispatchTransformedTouchEvent(ev, cancelChild, target.child, target.pointerIdBits)) {
handled = true;
}
if (cancelChild) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
}
}
return handled;
}
