Android焦点分发基础

   本文转载自：http://www.cnblogs.com/myzh/p/3664544.html?utm_source=tuicool&utm_medium=referral 请尊重原创

   

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<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;    }

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<View>() {                    @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, 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);        }    }

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