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来自天天博客：http://www.cnblogs.com/tiantianbyconan/p/7286503.html
通过View的View::focusSearch进行焦点搜索对应方向上的下一个可以获取焦点的View：
public View focusSearch(@FocusRealDirection int direction) {
if (mParent != null) {
return mParent.focusSearch(this, direction);
} else {
return null;
}
}
不断地调用父控件来进行搜索，focusSearch有两个实现：ViewGroup和RecyclerView，先看ViewGroup：
@Override
public View focusSearch(View focused, int direction) {
if (isRootNamespace()) {
// root namespace means we should consider ourselves the top of the
// tree for focus searching; otherwise we could be focus searching
// into other tabs. see LocalActivityManager and TabHost for more info
return FocusFinder.getInstance().findNextFocus(this, focused, direction);
} else if (mParent != null) {
return mParent.focusSearch(focused, direction);
}
return null;
}
如果是最顶层，则直接调用FocusFinder::findNextFocus方法进行搜索；否则调用父控件的focusSearch。FocusFinder::findNextFocus如下：
private View findNextFocus(ViewGroup root, View focused, Rect focusedRect, int direction) {
View next = null;
if (focused != null) {
next = findNextUserSpecifiedFocus(root, focused, direction);
}
if (next != null) {
return next;
}
ArrayList<View> focusables = mTempList;
try {
focusables.clear();
root.addFocusables(focusables, direction);
if (!focusables.isEmpty()) {
next = findNextFocus(root, focused, focusedRect, direction, focusables);
}
} finally {
focusables.clear();
}
return next;
}上面的root参数代表的是最顶层的view。
首先，通过尝试通过findNextUserSpecifiedFocus来查找下一个“指定的”可获得焦点的View，这个指定是开发者通过SDK自带的setNextFocusLeftId等方法进行手动设置的。如果查找到指定的下一个可获得焦点的View，则返回该View；否则，执行View::addFocusables方法，通过这个最顶层的View去拿到所有直接或间接的Focusable的子View，并添加到ArrayList<View> focusables中。
View::addFolcusables方法中有4种实现：
第一种是View中默认实现：
public void addFocusables(ArrayList<View> views, @FocusDirection int direction,
@FocusableMode int focusableMode) {
if (views == null) {
return;
}
if (!isFocusable()) {
return;
}
if ((focusableMode & FOCUSABLES_TOUCH_MODE) == FOCUSABLES_TOUCH_MODE
&& !isFocusableInTouchMode()) {
return;
}
views.add(this);
}如果自己是focusable的话，直接把自己添加进去。
第二种是ViewGroup实现：
@Override
public void addFocusables(ArrayList<View> views, int direction, int focusableMode) {
final int focusableCount = views.size();
final int descendantFocusability = getDescendantFocusability();
if (descendantFocusability != FOCUS_BLOCK_DESCENDANTS) {
if (shouldBlockFocusForTouchscreen()) {
focusableMode |= FOCUSABLES_TOUCH_MODE;
}
final int count = mChildrenCount;
final View[] children = mChildren;
for (int i = 0; i < count; i++) {
final View child = children[i];
if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE) {
child.addFocusables(views, direction, focusableMode);
}
}
}
// we add ourselves (if focusable) in all cases except for when we are
// FOCUS_AFTER_DESCENDANTS and there are some descendants focusable. this is
// to avoid the focus search finding layouts when a more precise search
// among the focusable children would be more interesting.
if ((descendantFocusability != FOCUS_AFTER_DESCENDANTS
// No focusable descendants
|| (focusableCount == views.size())) &&
(isFocusableInTouchMode() || !shouldBlockFocusForTouchscreen())) {
super.addFocusables(views, direction, focusableMode);
}
}先会处理自身ViewGroup与它后代的关系(descendantFocusability)，前面提到过，可能的几种情况：
- FOCUS_BEFORE_DESCENDANTS: ViewGroup本身先对焦点进行处理，如果没有处理则分发给child View进行处理
- FOCUS_AFTER_DESCENDANTS: 先分发给Child View进行处理，如果所有的Child View都没有处理，则自己再处理
- FOCUS_BLOCK_DESCENDANTS: ViewGroup本身进行处理，不管是否处理成功，都不会分发给ChildView进行处理
所以，以上：
- 如果不是
FOCUS_BLOCK_DESCENDANTS，则首先检查blockForTouchscreen并重置掉focusableMode，然后遍历所有的子View，调用child::addFocusables。 - 如果不是
FOCUS_AFTER_DESCENDANTS或者没有focusable的子View时自己处理，所以把自己加入到views中。
第三种是ViewPager实现：
@Override
public void addFocusables(ArrayList<View> views, int direction, int focusableMode) {
final int focusableCount = views.size();
final int descendantFocusability = getDescendantFocusability();
if (descendantFocusability != FOCUS_BLOCK_DESCENDANTS) {
for (int i = 0; i < getChildCount(); i++) {
final View child = getChildAt(i);
if (child.getVisibility() == VISIBLE) {
ItemInfo ii = infoForChild(child);
if (ii != null && ii.position == mCurItem) {
child.addFocusables(views, direction, focusableMode);
}
}
}
}
// we add ourselves (if focusable) in all cases except for when we are
// FOCUS_AFTER_DESCENDANTS and there are some descendants focusable. this is
// to avoid the focus search finding layouts when a more precise search
// among the focusable children would be more interesting.
if (descendantFocusability != FOCUS_AFTER_DESCENDANTS
|| (focusableCount == views.size())) { // No focusable descendants
// Note that we can't call the superclass here, because it will
// add all views in. So we need to do the same thing View does.
if (!isFocusable()) {
return;
}
if ((focusableMode & FOCUSABLES_TOUCH_MODE) == FOCUSABLES_TOUCH_MODE
&& isInTouchMode() && !isFocusableInTouchMode()) {
return;
}
if (views != null) {
views.add(this);
}
}
}与ViewGroup基本一致，在descendantFocusability不是FOCUS_BLOCK_DESCENDANTS时，遍历子View时判断view是否属于当前的page，如果是才加进去。如果不是FOCUS_AFTER_DESCENDANTS或者没有focusable的子View时自己处理，所以把自己加入到views中。
第四种是RecyclerView实现：
@Override
public void addFocusables(ArrayList<View> views, int direction, int focusableMode) {
if (mLayout == null || !mLayout.onAddFocusables(this, views, direction, focusableMode)) {
super.addFocusables(views, direction, focusableMode);
}
}通过LayoutManager::onAddFocusables来进行管理，如果返回false，则直接调用父类ViewGroup的方法，看下LayoutManager::onAddFocusables的实现：
public boolean onAddFocusables(RecyclerView recyclerView, ArrayList<View> views,
int direction, int focusableMode) {
return false;
}直接返回false，并且没有看到相关的LayoutManager对该方法的重写，所以，这里应该是直接调用了父类ViewGroup的方法。
addFocusables方法完毕，回到 FocusFinder::findNextFocus 方法中通过root.addFocusables(focusables, direction);加入所有可获取焦点的View之后，在非空的情况下调用如下代码：
next = findNextFocus(root, focused, focusedRect, direction, focusables);所以重点是FocusFinder::findNextFocus方法的实现：
private View findNextFocus(ViewGroup root, View focused, Rect focusedRect,
int direction, ArrayList<View> focusables) {
if (focused != null) {
if (focusedRect == null) {
focusedRect = mFocusedRect;
}
// fill in interesting rect from focused
focused.getFocusedRect(focusedRect);
root.offsetDescendantRectToMyCoords(focused, focusedRect);
} else {
if (focusedRect == null) {
focusedRect = mFocusedRect;
// make up a rect at top left or bottom right of root
switch (direction) {
case View.FOCUS_RIGHT:
case View.FOCUS_DOWN:
setFocusTopLeft(root, focusedRect);
break;
case View.FOCUS_FORWARD:
if (root.isLayoutRtl()) {
setFocusBottomRight(root, focusedRect);
} else {
setFocusTopLeft(root, focusedRect);
}
break;
case View.FOCUS_LEFT:
case View.FOCUS_UP:
setFocusBottomRight(root, focusedRect);
break;
case View.FOCUS_BACKWARD:
if (root.isLayoutRtl()) {
setFocusTopLeft(root, focusedRect);
} else {
setFocusBottomRight(root, focusedRect);
break;
}
}
}
}
switch (direction) {
case View.FOCUS_FORWARD:
case View.FOCUS_BACKWARD:
return findNextFocusInRelativeDirection(focusables, root, focused, focusedRect,
direction);
case View.FOCUS_UP:
case View.FOCUS_DOWN:
case View.FOCUS_LEFT:
case View.FOCUS_RIGHT:
return findNextFocusInAbsoluteDirection(focusables, root, focused,
focusedRect, direction);
default:
throw new IllegalArgumentException("Unknown direction: " + direction);
}
}- 如果focused不是null，说明当前获取到焦点的View存在，则获得绘制焦点的Rect到focusedRect，然后根据rootView遍历所有ParentView从子View纠正坐标到根View坐标。
- 如果focused是null，则说明当前没有View获取到焦点，则把focusedRect根据不同的direction重置为“一点”。
最后根据direction调用FocusFinder::findNextFocusInAbsoluteDirection方法进行对比查找“下一个”View。
View findNextFocusInAbsoluteDirection(ArrayList<View> focusables, ViewGroup root, View focused,
Rect focusedRect, int direction) {
// initialize the best candidate to something impossible
// (so the first plausible view will become the best choice)
mBestCandidateRect.set(focusedRect);
switch(direction) {
case View.FOCUS_LEFT:
mBestCandidateRect.offset(focusedRect.width() + 1, 0);
break;
case View.FOCUS_RIGHT:
mBestCandidateRect.offset(-(focusedRect.width() + 1), 0);
break;
case View.FOCUS_UP:
mBestCandidateRect.offset(0, focusedRect.height() + 1);
break;
case View.FOCUS_DOWN:
mBestCandidateRect.offset(0, -(focusedRect.height() + 1));
}
View closest = null;
int numFocusables = focusables.size();
for (int i = 0; i < numFocusables; i++) {
View focusable = focusables.get(i);
// only interested in other non-root views
if (focusable == focused || focusable == root) continue;
// get focus bounds of other view in same coordinate system
focusable.getFocusedRect(mOtherRect);
root.offsetDescendantRectToMyCoords(focusable, mOtherRect);
if (isBetterCandidate(direction, focusedRect, mOtherRect, mBestCandidateRect)) {
mBestCandidateRect.set(mOtherRect);
closest = focusable;
}
}
return closest;
}首先把最优选择mBestCandidateRect设置为focusedRect，根据方向做1像素的偏移便于对比。遍历所有刚刚查询出来的focusables，拿到每一个的focusedRect区域并进行转换，然后通过FocusFinder::isBetterCandidate方法进行对比，然后拿到更好的，遍历完成后就是最优选择。接下来看下FocusFinder::isBetterCandidate方法来了解下是怎么做对比的：
下面代码意思是：以source这个rect来说，作为对应derection上下一个focus view，rect1是否比rect2更优？
boolean isBetterCandidate(int direction, Rect source, Rect rect1, Rect rect2) {
// to be a better candidate, need to at least be a candidate in the first
// place :)
if (!isCandidate(source, rect1, direction)) {
return false;
}
// we know that rect1 is a candidate.. if rect2 is not a candidate,
// rect1 is better
if (!isCandidate(source, rect2, direction)) {
return true;
}
// if rect1 is better by beam, it wins
if (beamBeats(direction, source, rect1, rect2)) {
return true;
}
// if rect2 is better, then rect1 cant' be :)
if (beamBeats(direction, source, rect2, rect1)) {
return false;
}
// otherwise, do fudge-tastic comparison of the major and minor axis
return (getWeightedDistanceFor(
majorAxisDistance(direction, source, rect1),
minorAxisDistance(direction, source, rect1))
< getWeightedDistanceFor(
majorAxisDistance(direction, source, rect2),
minorAxisDistance(direction, source, rect2)));
}首先确定rect1是否isCandidate？isCandidate做的逻辑简单来说就是确定rect是否满足给定的derection作为下一个focus view这个条件，它的判断依据如下：
boolean isCandidate(Rect srcRect, Rect destRect, int direction) {
switch (direction) {
case View.FOCUS_LEFT:
return (srcRect.right > destRect.right || srcRect.left >= destRect.right)
&& srcRect.left > destRect.left;
case View.FOCUS_RIGHT:
return (srcRect.left < destRect.left || srcRect.right <= destRect.left)
&& srcRect.right < destRect.right;
case View.FOCUS_UP:
return (srcRect.bottom > destRect.bottom || srcRect.top >= destRect.bottom)
&& srcRect.top > destRect.top;
case View.FOCUS_DOWN:
return (srcRect.top < destRect.top || srcRect.bottom <= destRect.top)
&& srcRect.bottom < destRect.bottom;
}
throw new IllegalArgumentException("direction must be one of "
+ "{FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, FOCUS_RIGHT}.");
}代码比较简单。再回到 FocusFinder::isBetterCandidate 的代码逻辑：
- 如果rect1不满足基本条件，则肯定返回false（基本的条件都不满足）
- 如果rect2不满足基本条件，则返回true，认为rect1更优
- 如果都满足基本条件的情况下，通过
FocusFinder::beamBeats方法来判断哪种更优
接下来看下FocusFinder::beamBeats的实现：
boolean beamBeats(int direction, Rect source, Rect rect1, Rect rect2) {
final boolean rect1InSrcBeam = beamsOverlap(direction, source, rect1);
final boolean rect2InSrcBeam = beamsOverlap(direction, source, rect2);
// if rect1 isn't exclusively in the src beam, it doesn't win
if (rect2InSrcBeam || !rect1InSrcBeam) {
return false;
}
// we know rect1 is in the beam, and rect2 is not
// if rect1 is to the direction of, and rect2 is not, rect1 wins.
// for example, for direction left, if rect1 is to the left of the source
// and rect2 is below, then we always prefer the in beam rect1, since rect2
// could be reached by going down.
if (!isToDirectionOf(direction, source, rect2)) {
return true;
}
// for horizontal directions, being exclusively in beam always wins
if ((direction == View.FOCUS_LEFT || direction == View.FOCUS_RIGHT)) {
return true;
}
// for vertical directions, beams only beat up to a point:
// now, as long as rect2 isn't completely closer, rect1 wins
// e.g for direction down, completely closer means for rect2's top
// edge to be closer to the source's top edge than rect1's bottom edge.
return (majorAxisDistance(direction, source, rect1)
< majorAxisDistanceToFarEdge(direction, source, rect2));
}首先通过beamsOverlap方法来判断两个rect与source是否重叠等等。注意的是，在水平情况下，如果rect1重叠，则就是最优解（为什么？比较奇怪），最后如果是竖直情况，通过FocusFinder::majorAxisDistance方法来判断哪个离source最近。如果还是比较不出，则通过getWeightedDistanceFor方法来通过“主要距离”和“次要距离”做一个综合的比较。
RecyclerView
继续 focusSearch 代码的分析，刚刚只跟了ViewGroup，还有一个实现是RecyclerView的实现：
@Override
public View focusSearch(View focused, int direction) {
View result = mLayout.onInterceptFocusSearch(focused, direction);
if (result != null) {
return result;
}
// ...
}首先通过onInterceptFocusSearch进行拦截，如果返回具体的focus View，则直接返回；否则继续往下；onInterceptFocusSearch实现如下：
public View onInterceptFocusSearch(View focused, int direction) {
return null;
}默认为空实现，返回null，也没有其它的子类进行重写，所以暂时不管这个处理，继续看focusSearch：
@Override
public View focusSearch(View focused, int direction) {
View result = mLayout.onInterceptFocusSearch(focused, direction);
if (result != null) {
return result;
}
final boolean canRunFocusFailure = mAdapter != null && mLayout != null
&& !isComputingLayout() && !mLayoutFrozen;
final FocusFinder ff = FocusFinder.getInstance();
if (canRunFocusFailure
&& (direction == View.FOCUS_FORWARD || direction == View.FOCUS_BACKWARD)) {
// convert direction to absolute direction and see if we have a view there and if not
// tell LayoutManager to add if it can.
boolean needsFocusFailureLayout = false;
if (mLayout.canScrollVertically()) {
final int absDir =
direction == View.FOCUS_FORWARD ? View.FOCUS_DOWN : View.FOCUS_UP;
final View found = ff.findNextFocus(this, focused, absDir);
needsFocusFailureLayout = found == null;
if (FORCE_ABS_FOCUS_SEARCH_DIRECTION) {
// Workaround for broken FOCUS_BACKWARD in API 15 and older devices.
direction = absDir;
}
}
if (!needsFocusFailureLayout && mLayout.canScrollHorizontally()) {
boolean rtl = mLayout.getLayoutDirection() == ViewCompat.LAYOUT_DIRECTION_RTL;
final int absDir = (direction == View.FOCUS_FORWARD) ^ rtl
? View.FOCUS_RIGHT : View.FOCUS_LEFT;
final View found = ff.findNextFocus(this, focused, absDir);
needsFocusFailureLayout = found == null;
if (FORCE_ABS_FOCUS_SEARCH_DIRECTION) {
// Workaround for broken FOCUS_BACKWARD in API 15 and older devices.
direction = absDir;
}
}
if (needsFocusFailureLayout) {
consumePendingUpdateOperations();
final View focusedItemView = findContainingItemView(focused);
if (focusedItemView == null) {
// panic, focused view is not a child anymore, cannot call super.
return null;
}
eatRequestLayout();
mLayout.onFocusSearchFailed(focused, direction, mRecycler, mState);
resumeRequestLayout(false);
}
result = ff.findNextFocus(this, focused, direction);
} else {
result = ff.findNextFocus(this, focused, direction);
if (result == null && canRunFocusFailure) {
consumePendingUpdateOperations();
final View focusedItemView = findContainingItemView(focused);
if (focusedItemView == null) {
// panic, focused view is not a child anymore, cannot call super.
return null;
}
eatRequestLayout();
result = mLayout.onFocusSearchFailed(focused, direction, mRecycler, mState);
resumeRequestLayout(false);
}
}
if (result != null && !result.hasFocusable()) {
if (getFocusedChild() == null) {
// Scrolling to this unfocusable view is not meaningful since there is no currently
// focused view which RV needs to keep visible.
return super.focusSearch(focused, direction);
}
// If the next view returned by onFocusSearchFailed in layout manager has no focusable
// views, we still scroll to that view in order to make it visible on the screen.
// If it's focusable, framework already calls RV's requestChildFocus which handles
// bringing this newly focused item onto the screen.
requestChildOnScreen(result, null);
return focused;
}
return isPreferredNextFocus(focused, result, direction)
? result : super.focusSearch(focused, direction);
}我们暂时只考虑direction为left，top，right，down的情况，则进入最外面if的else分支：
public View focusSearch(View focused, int direction) {
// ...
result = ff.findNextFocus(this, focused, direction);
if (result == null && canRunFocusFailure) {
consumePendingUpdateOperations();
final View focusedItemView = findContainingItemView(focused);
if (focusedItemView == null) {
// panic, focused view is not a child anymore, cannot call super.
return null;
}
eatRequestLayout();
result = mLayout.onFocusSearchFailed(focused, direction, mRecycler, mState);
resumeRequestLayout(false);
}
// ...
}首先通过FocusFinder::findNextFocus方法来获取下一个应该获得焦点的View，这里获取的结果与 FocusFinder::findNextFocus 逻辑一致。