2024年8月24日发(作者：)
Android焦点事件分发与传递机制
下面我们就从源码来带大家进行安卓TV焦点事件的传递
这里先给出Android系统View的绘制流程：
依次执行View类里面的如下三个方法：
measure(int ,int) :测量View的大小
layout(int ,int ,int ,int) ：设置子View的位置
draw(Canvas) ：绘制View内容到Canvas画布上
ViewRootImpl的主要作用如下（此处不多讲，如有意图，看源码）：
A：链接WindowManager和DecorView的纽带，更广一点可以说是Window和View之间的
纽带。
B：完成View的绘制过程，包括measure、layout、draw过程。
C：向DecorView分发收到的用户发起的event事件，如按键，触屏等事件。
ViewRootImpl不再多余叙述，进入正题：
Android焦点分发的主要方法以及拦截方法的讲解。
在RootViewImpl中的函数通道是各种策略（InputStage）的组合，各策略负责的任务不同，
如SyntheticInputStage、ViewPostImeInputStage、NativePostImeInputStage等等，这些策略以
链表结构结构起来，当一个策略者没有消费事件时，就传递个下一个策略者。其中触摸和按
键事件由ViewPostImeInputStage处理。
@Override
protected int onProcess(QueuedInputEvent q) {
if ( instanceof KeyEvent) {
return processKeyEvent(q);//如果是按键事件走此处，处理按键和焦点问题
了
} else {
final int source = rce();
if ((source & _CLASS_POINTER) != 0) {
return processPointerEvent(q);//如果是触摸事件走此处
} else if ((source & _CLASS_TRACKBALL) != 0) {
return processTrackballEvent(q);
} else {
return processGenericMotionEvent(q);
}
}
}
processKeyEvent(QueuedInputEvent q)源码如下：
@Override
protected void onDeliverToNext(QueuedInputEvent q) {
if (mUnbufferedInputDispatch
&& instanceof MotionEvent
&& ((MotionEvent)).isTouchEvent()
&& isTerminalInputEvent()) {
mUnbufferedInputDispatch = false;
scheduleConsumeBatchedInput();
}
verToNext(q);
}
private int processKeyEvent(QueuedInputEvent q) {
final KeyEvent event = (KeyEvent);
// Deliver the key to the view hierarchy.
if (chKeyEvent(event)) {
return FINISH_HANDLED;
}
if (shouldDropInputEvent(q)) {
return FINISH_NOT_HANDLED;
}
// If the Control modifier is held, try to interpret the key as a shortcut.
if (ion() == _DOWN
&& Pressed()
&& eatCount() == 0
&& !fierKey(Code())) {
if (chKeyShortcutEvent(event)) {
return FINISH_HANDLED;
}
if (shouldDropInputEvent(q)) {
return FINISH_NOT_HANDLED;
}
}
// Apply the fallback event policy.
if (chKeyEvent(event)) {
return FINISH_HANDLED;
}
if (shouldDropInputEvent(q)) {
return FINISH_NOT_HANDLED;
}
// Handle automatic focus changes.
if (ion() == _DOWN) {
int direction = 0;
switch (Code()) {
case E_DPAD_LEFT:
if (odifiers()) {
direction = _LEFT;
}
break;
case E_DPAD_RIGHT:
if (odifiers()) {
direction = _RIGHT;
}
break;
case E_DPAD_UP:
if (odifiers()) {
direction = _UP;
}
break;
case E_DPAD_DOWN:
if (odifiers()) {
direction = _DOWN;
}
break;
case E_TAB:
if (odifiers()) {
direction = _FORWARD;
} else if (ifiers(_SHIFT_ON)) {
direction = _BACKWARD;
}
break;
}
if (direction != 0) {
View focused = cus();
if (focused != null) {
View v = earch(direction);
if (v != null && v != focused) {
// do the math the get the interesting rect
// of previous focused into the coord system of
// newly focused view
usedRect(mTempRect);
if (mView instanceof ViewGroup) {
((ViewGroup)
mView).offsetDescendantRectToMyCoords(
focused, mTempRect);
((ViewGroup) mView).offsetRectIntoDescendantCoords(
v, mTempRect);
}
if (tFocus(direction, mTempRect)) {
playSoundEffect(SoundEffectConstants
.getContantForFocusDirection(direction));
return FINISH_HANDLED;
}
}
// Give the focused view a last chance to handle the dpad key.
if (chUnhandledMove(focused, direction)) {
return FINISH_HANDLED;
}
} else {
// find the best view to give focus to in this non-touch-mode with
no-focus
View v = focusSearch(null, direction);
if (v != null && tFocus(direction)) {
return FINISH_HANDLED;
}
}
}
}
return FORWARD;
}
进入源码讲解：
(1) 首先由dispatchKeyEvent进行焦点的分发
如果dispatchKeyEvent方法返回true，那么下面的焦点查找步骤就不会继续了。
dispatchKeyEvent方法返回true代表事件（包括焦点和按键）被消费了。
dispatchKeyEvent(event)如果不了解，看我上一篇文章安卓TounchEvent事件分发机制。
mView的dispatchKeyEvent方法，
mView是是Activity的顶层容器DecorView，它是一FrameLayout。
所以这里的dispatchKeyEvent方法应该执行的是ViewGroup的dispatchKeyEvent()方法，而
不是View的dispatchKeyEvent方法。
@Override
public boolean dispatchKeyEvent(KeyEvent event) {
if (mInputEventConsistencyVerifier != null) {
vent(event, 1);
}
if ((mPrivateFlags & (PFLAG_FOCUSED | PFLAG_HAS_BOUNDS))
== (PFLAG_FOCUSED | PFLAG_HAS_BOUNDS)) {
if (chKeyEvent(event)) {
return true;
}
} else if (mFocused != null && (teFlags & PFLAG_HAS_BOUNDS)
== PFLAG_HAS_BOUNDS) {
if (chKeyEvent(event)) {
return true;
}
}
if (mInputEventConsistencyVerifier != null) {
ndledEvent(event, 1);
}
return false;
}
ViewGroup的dispatchKeyEvent简略执行流程
首先ViewGroup会执行父类的dispatchKeyEvent方法，如果返回true那么父类的
dispatchKeyEvent方法就会返回true，也就代表父类消费了该焦点事件，那么焦点事件自然
就不会往下进行分发。
然后ViewGroup会判断mFocused这个view是否为空，如果为空就会****return false，
焦点继续往下传递；如果不为空，那就会return mFocused的dispatchKeyEvent方法返回的
结果。这个mFocused是ViewGroup中当前获取焦点的子View，这个可以从requestChildFocus
方法中得到答案。
requestChildFocus()的源码如下：
@Override
public void requestChildFocus(View child, View focused) {
if (DBG) {
n(this + " requestChildFocus()");
}
if (getDescendantFocusability() == FOCUS_BLOCK_DESCENDANTS) {
return;
}
// Unfocus us, if necessary
s(focused);
// We had a previous notion of who had focus. Clear it.
if (mFocused != child) {
if (mFocused != null) {
s(focused);
}
mFocused = child;
}
if (mParent != null) {
tChildFocus(this, focused);
}
}
View的dispatchKeyEvent简略执行流程
public boolean dispatchKeyEvent(KeyEvent event) {
if (mInputEventConsistencyVerifier != null) {
vent(event, 0);
}
// Give any attached key listener a first crack at the event.
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && Listener != null && (mViewFlags &
ENABLED_MASK) == ENABLED
&& (this, Code(), event)) {
return true;
}
if (ch(this, mAttachInfo != null
? spatchState : null, this)) {
return true;
}
if (mInputEventConsistencyVerifier != null) {
ndledEvent(event, 0);
}
return false;
}
要修改ViewGroup焦点事件的分发：
重写view的dispatchKeyEvent方法
给某个子view设置onKeyListener监听
焦点没有被dispatchKeyEvent拦截的情况下的继续代码中的处理过程，还是进入
ViewRootImpl源码
// Handle automatic focus changes.
if (ion() == _DOWN) {
int direction = 0;
switch (Code()) {
case E_DPAD_LEFT:
if (odifiers()) {
direction = _LEFT;
}
break;
case E_DPAD_RIGHT:
if (odifiers()) {
direction = _RIGHT;
}
break;
case E_DPAD_UP:
if (odifiers()) {
direction = _UP;
}
break;
case E_DPAD_DOWN:
if (oModifiers()) {
direction = _DOWN;
}
break;
case E_TAB:
if (odifiers()) {
direction = _FORWARD;
} else if (ifiers(_SHIFT_ON)) {
direction = _BACKWARD;
}
break;
}
if (direction != 0) {
View focused = cus();
if (focused != null) {
View v = earch(direction);
if (v != null && v != focused) {
// do the math the get the interesting rect
// of previous focused into the coord system of
// newly focused view
usedRect(mTempRect);
if (mView instanceof ViewGroup) {
((ViewGroup)
mView).offsetDescendantRectToMyCoords(
focused, mTempRect);
((ViewGroup)
mView).offsetRectIntoDescendantCoords(
v, mTempRect);
}
if (tFocus(direction, mTempRect)) {
playSoundEffect(SoundEffectConstants
.getContantForFocusDirection(direction));
return FINISH_HANDLED;
}
}
// Give the focused view a last chance to handle the dpad key.
if (chUnhandledMove(focused, direction)) {
return FINISH_HANDLED;
}
} else {
// find the best view to give focus to in this non-touch-mode
with no-focus
View v = focusSearch(null, direction);
if (v != null && tFocus(direction)) {
return FINISH_HANDLED;
}
}
}
}
dispatchKeyEvent方法返回false后，先得到按键的方向direction一个int值。direction
值是后面来进行焦点查找的。
接着会调用DecorView的findFocus()方法一层一层往下查找已经获取焦点的子View。
DecorView则是PhoneWindow类的一个内部类，继承于FrameLayout，由此可知它是一
个ViewGroup。
那么，DecroView到底充当了什么样的角色呢？
其实，DecorView是整个ViewTree的最顶层View，它是一个FrameLayout布局，代表
了整个应用的界面。在该布局下面，有标题view和内容view这两个子元素。
@Override
public View findFocus() {
if (DBG) {
n("Find focus in " + this + ": flags="
+ isFocused() + ", child=" + mFocused);
}
if (isFocused()) {
return this;
}
if (mFocused != null) {
return cus();
}
return null;
}
View的findFocus方法
/**
* Find the view in the hierarchy rooted at this view that currently has
* focus.
*
* @return The view that currently has focus, or null if no focused view can
* be found.
*/
public View findFocus() {
return (mPrivateFlags & PFLAG_FOCUSED) != 0 ? this : null;
}
View的hasFocus()方法和isFocused()方法对比
Stackoverflow解释来了：
hasFocus() is different from isFocused(). hasFocus() == true means that the View or one of
its descendants is focused. If you look closely, there’s a chain of hasFocused Views till you reach
the View that isFocused.
/**
* Returns true if this view has focus itself, or is the ancestor of the
* view that has focus.
*
* @return True if this view has or contains focus, false otherwise.
*/
@edProperty(category = "focus")
public boolean hasFocus() {
return (mPrivateFlags & PFLAG_FOCUSED) != 0;
}
/**
* Returns true if this view has focus
*
* @return True if this view has focus, false otherwise.
*/
@edProperty(category = "focus")
public isFocused() {
return (mPrivateFlags & PFLAG_FOCUSED) != 0;
}
接着，如果cus()方法返回的mFocused不为空，说明找到了当前获取焦点
的view（mFocused），接着focusSearch会把direction（遥控器按键按下的方向）作为参数，
找到特定方向下一个将要获取焦点的view，最后如果该view不为空，那么就让该view获
取焦点。
我们来看一下focusSearch方法的源码以及具体实现。
@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 tance().findNextFocus(this, focused, direction);
} else if (mParent != null) {
return earch(focused, direction);
}
return null;
}
focusSearch其实是一层一层地网上调用父View的focusSearch方法，直到当前view是
根布局（isRootNamespace()方法），通过注释可以知道focusSearch最终会调用DecorView的
focusSearch方法。而DecorView的focusSearch方法找到的焦点view是通过FocusFinder来
找到的。
FocusFinder是什么？
根据给定的按键方向，通过当前的获取焦点的View，查找下一个获取焦点的view这样
算法的类。焦点没有被拦截的情况下，Android焦点的查找最终都是通过FocusFinder类来
实现的。
FocusFinder是如何通过findNextFocus方法寻找焦点的？
public final View findNextFocus(ViewGroup root, View focused, int direction) {
return findNextFocus(root, focused, null, direction);
}
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
try {
();
usables(focusables, direction);
if (!y()) {
next = findNextFocus(root, focused, focusedRect, direction, focusables);
}
} finally {
();
}
return next;
}
private View findNextFocus(ViewGroup root, View focused, Rect focusedRect,
int direction, ArrayList
if (focused != null) {
if (focusedRect == null) {
focusedRect = mFocusedRect;
}
// fill in interesting rect from focused
usedRect(focusedRect);
DescendantRectToMyCoords(focused, focusedRect);
} else {
if (focusedRect == null) {
focusedRect = mFocusedRect;
// make up a rect at top left or bottom right of root
switch (direction) {
case _RIGHT:
case _DOWN:
setFocusTopLeft(root, focusedRect);
break;
case _FORWARD:
if (utRtl()) {
setFocusBottomRight(root, focusedRect);
} else {
setFocusTopLeft(root, focusedRect);
}
break;
case _LEFT:
case _UP:
setFocusBottomRight(root, focusedRect);
break;
case _BACKWARD:
if (utRtl()) {
setFocusTopLeft(root, focusedRect);
} else {
setFocusBottomRight(root, focusedRect);
break;
}
}
}
}
private View findNextUserSpecifiedFocus(ViewGroup root, View focused, int direction)
{
// check for user specified next focus
View userSetNextFocus = erSetNextFocus(root, direction);
if (userSetNextFocus != null && sable()
&& (!uchMode()
|| sableInTouchMode())) {
return userSetNextFocus;
}
return null;
}
FocusFinder类通过findNextFocus来找焦点的。一层一层往寻找，后面会执行
findNextUserSpecifiedFocus()方法，这个方法会执行focused(即当前获取焦点的View)的
findUserSetNextFocus方法，如果该方法返回的View不为空，
且isFocusable = true && isInTouchMode() = true的话。
FocusFinder找到的焦点就是findNextUserSpecifiedFocus()返回的View。
findNextFocus会优先根据XML里设置的下一个将获取焦点的View的ID值来寻找将
要获取焦点的View。
View findUserSetNextFocus(View root, @FocusDirection int direction) {
switch (n) {
case FOCUS_LEFT:
if (mNextFocusLeftId == _ID) return null;
return findViewInsideOutShouldExist(root, mNextFocusLeftId);
case FOCUS_RIGHT:
if (mNextFocusRightId == _ID) return null;
return findViewInsideOutShouldExist(root, mNextFocusRightId);
case FOCUS_UP:
if (mNextFocusUpId == _ID) return null;
return findViewInsideOutShouldExist(root, mNextFocusUpId);
case FOCUS_DOWN:
if (mNextFocusDownId == _ID) return null;
return findViewInsideOutShouldExist(root, mNextFocusDownId);
case FOCUS_FORWARD:
if (mNextFocusForwardId == _ID) return null;
return findViewInsideOutShouldExist(root, mNextFocusForwardId);
case FOCUS_BACKWARD: {
if (mID == _ID) return null;
final int id = mID;
return ewByPredicateInsideOut(this, new Predicate
{
@Override
public boolean apply(View t) {
return ocusForwardId == id;
}
});
}
}
return null;
}
焦点事件分发步骤：
DecorView会调用dispatchKey一层一层进行焦点的分发，如果dispatchKeyEvent方法
返回true的话，那么焦点或者按键事件就不会往下分发了。
如果你想拦截某个子View，对其设置OnKeyListener进行焦点的拦截。
如果焦点没有被拦截的话，那么焦点就会交给系统来处理,还是会继续分发，直到找到
那个获取焦点的View
Android底层先会记录按键的方向，后面DecorView会一层一层往下调用findFocus方
法找到当前获取焦点的View
后面系统又会根据按键的方向，执行focusSearch方法来寻找下一个将要获取焦点的
View
focusSearch内部其实是通过FocusFinder来查找焦点的。FocusFinder会优先通过View
在XML布局设置的下一个焦点的ID来查找焦点。
最终如果找到将要获取焦点的View，就让其requestFocus。如果请求无效，将其放在
onWindowFocusChanged（）这个方法中去请求。这是在Activity寻找到焦点的时候。
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