[Android]Android焦点流程代码分析
以下内容为原创，欢迎转载，转载请注明 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。
