焦点处理相关记录
以下所涉及的焦点部分，只是按键移动部分，不明确包含Touch Focus部分
需解决问题
控件的下一个焦点是哪？
分析思路
当用户通过按键（遥控器等）触发焦点切换时，事件指令会通过底层进行一系列处理。
在ViewRootImpl.java中有一个方法,deliverKeyEventPostIme(...),因为涉及到底层代码，所以没有详细的跟踪分析此方法的调用逻辑,根据网上的资料,按键相关的处理会经过此方法。private void deliverKeyEventPostIme(QueuedInputEvent q) { ... // Handle automatic focus changes. if (event.getAction() == KeyEvent.ACTION_DOWN) { int direction = 0; switch (event.getKeyCode()) { case KeyEvent.KEYCODE_DPAD_LEFT: if (event.hasNoModifiers()) { direction = View.FOCUS_LEFT; } break; case KeyEvent.KEYCODE_DPAD_RIGHT: if (event.hasNoModifiers()) { direction = View.FOCUS_RIGHT; } break; ... } if (direction != 0) { View focused = mView.findFocus(); if (focused != null) { View v = focused.focusSearch(direction); if (v != null && v != focused) { ..... if (v.requestFocus(direction, mTempRect)) { ...finishInputEvent(q, true); return; } } ... } } 由此方法可以看出，最主要的两个核心过程：
View v = focused.focusSearch(direction); v.requestFocus(direction, mTempRect)
接下来详细的分析下，看看过程中进行了什么操作
具体分析
在具体分析前,首先我们先明确下相关变量的定义
View mView : 主体View[DecorView]
//一般把主View“DecorView”添加到WindowManagerImpl中(通过addView) //WindowManagerImpl.java private void addView(View view...) { ViewRootImpl root; root = new ViewRootImpl(view.getContext()); ... root.setView(view, wparams, panelParentView); ... } //ViewRootImpl.java public void setView(View view....) { synchronized (this) { if (mView == null) { mView = view; ... } ... } } 所以mView是一个DecorView类型的变量.
View focused :
View focused = mView.findFocus(); //PhoneWindow.java private final class DecorView extends FrameLayout implements RootVie.... { ... } //FrameLayout.java public class FrameLayout extends ViewGroup { ... } //ViewGroup.java //mFocused记录的是当前被焦点选中的view @Override public View findFocus() { if (DBG) { System.out.println("Find focus in " + this + ": flags=" + isFocused() + ", child=" + mFocused); } if (isFocused()) { return this; } if (mFocused != null) { return mFocused.findFocus(); } return null; } 所以最终得到的focused为当前页面中得到焦点的view.
在明确的相关变量后,我们开始View v = focused.focusSearch(direction)的具体分析.
//View.java public View focusSearch(int direction) { //如果存在父控件,则执行父控件的focusSearch方法 if (mParent != null) { return mParent.focusSearch(this, direction); } else { return null; } } //ViewGroup.java public View focusSearch(View focused, int direction) { //判断是否为顶层布局,若是则执行对应方法,若不是则继续向上寻找,说明会从内到外的一层层进行判断，直到最外层的布局为止 if (isRootNamespace()) { return FocusFinder.getInstance().findNextFocus(this, focused, direction); } else if (mParent != null) { return mParent.focusSearch(focused, direction); } return null; } 说明在这个过程中,其实是从里层开始一直遍历到最外层布局，然后在最外层布局将处理交给了FocusFinder中的方法.
FocusFinder.getInstance().findNextFocus(this, focused, direction);
那我们来看看此方法具体做了什么操作
//FocusFinder.java public final View findNextFocus(ViewGroup root, View focused, int direction) { return findNextFocus(root, focused, null, direction); } //FocusFinder.java 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 focusables = mTempList; try { focusables.clear(); root.addFocusables(focusables, direction); if (!focusables.isEmpty()) { next = findNextFocus(root, focused, focusedRect, direction, focusables); } } finally { focusables.clear(); } return next; } 发现在findNextFocus的执行过程的开始，先执行了findNextUserSpecifiedFocus(...)方法,由代码可以看出，此方法先去判断特定Id值是否存在,若存在则查询出Id对应的view.其实这些Id就是xml里通过android:nextFocusUp="..."等或者代码特别指定的焦点顺序.所以在此过程先判断，若存在,说明下个焦点已经找到,直接返回.
//FocusFinder.java private View findNextUserSpecifiedFocus(ViewGroup root, View focused, int direction) { // check for user specified next focus View userSetNextFocus = focused.findUserSetNextFocus(root, direction); if (userSetNextFocus != null && userSetNextFocus.isFocusable() && (!userSetNextFocus.isInTouchMode() || userSetNextFocus.isFocusableInTouchMode())) { return userSetNextFocus; } return null; } //View.java View findUserSetNextFocus(View root, int direction) { switch (direction) { case FOCUS_LEFT: if (mNextFocusLeftId == View.NO_ID) return null; return findViewInsideOutShouldExist(root, mNextFocusLeftId); case FOCUS_RIGHT: if (mNextFocusRightId == View.NO_ID) return null; return findViewInsideOutShouldExist(root, mNextFocusRightId); case FOCUS_UP: if (mNextFocusUpId == View.NO_ID) return null; return findViewInsideOutShouldExist(root, mNextFocusUpId); case FOCUS_DOWN: if (mNextFocusDownId == View.NO_ID) return null; return findViewInsideOutShouldExist(root, mNextFocusDownId); case FOCUS_FORWARD: if (mNextFocusForwardId == View.NO_ID) return null; return findViewInsideOutShouldExist(root, mNextFocusForwardId); case FOCUS_BACKWARD: { if (mID == View.NO_ID) return null; final int id = mID; return root.findViewByPredicateInsideOut(this, new Predicate () { @Override public boolean apply(View t) { return t.mNextFocusForwardId == id; } }); } } return null; } 如果上面过程没有查询到，则会执行到findNextFocus(...)方法.在这个方法中，先通过offsetDescendantRectToMyCoords(...)方法获得焦点控件的位置矩阵.然后通过比较得到下一个焦点的控件。具体的比较规则可以查看findNextFocusInRelativeDirection(...)方法与findNextFocusInAbsoluteDirection(...)方法.
//FocusFinder.java private View findNextFocus(ViewGroup root, View focused, Rect focusedRect, int direction, ArrayListfocusables) { 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); } }
结论
查找焦点的过程，主要是从View的focusSearch(...)方法开始,从当前焦点开始逐层往外,最终在最外层布局执行FocusFinder中的核心方法来获得下个焦点所在的视图view.
如果需要指定跳转，可以在逐层focusSearch(...)的时候，返回特定的view