ViewRootImpl中的类部类ViewPostImeInputStage.processKeyEvent(QueuedInputEvent q)--->DecorView.dispatchKeyEvent(event)
--->Activity.dispatchKeyEvent(event)
dispatchKeyEvent()执行流程
DecorView →PhoneWindow →Activity→ViewGroup→view
下面我们根据按键事件的分发流程，抽丝剥茧，逐一分析。
一、按键事件的入口：
private int processKeyEvent(QueuedInputEvent q)
ViewRootImpl.java-->ViewPostImeInputStage.processKeyEvent(QueuedInputEvent q)
private int processKeyEvent(QueuedInputEvent q) {
final KeyEvent event = (KeyEvent)q.mEvent;
if (mUnhandledKeyManager.preViewDispatch(event)) {
return FINISH_HANDLED;
}
//分发按键事件到视图树，mView即是DecorView
//DecorView继承FrameLayout,FrameLayout继承ViewGroup，
// DecorView.dispatchKeyEvent(event)重写了父类ViewGroup.dispatchKeyEvent(event)方法
// Deliver the key to the view hierarchy.
if (mView.dispatchKeyEvent(event)) {
return FINISH_HANDLED;
}
if (shouldDropInputEvent(q)) {
return FINISH_NOT_HANDLED;
}
// This dispatch is for windows that don't have a Window.Callback. Otherwise,
// the Window.Callback usually will have already called this (see
// DecorView.superDispatchKeyEvent) leaving this call a no-op.
if (mUnhandledKeyManager.dispatch(mView, event)) {
return FINISH_HANDLED;
}
int groupNavigationDirection = 0;
if (event.getAction() == KeyEvent.ACTION_DOWN
&& event.getKeyCode() == KeyEvent.KEYCODE_TAB) {
if (KeyEvent.metaStateHasModifiers(event.getMetaState(), KeyEvent.META_META_ON)) {
groupNavigationDirection = View.FOCUS_FORWARD;
} else if (KeyEvent.metaStateHasModifiers(event.getMetaState(),
KeyEvent.META_META_ON | KeyEvent.META_SHIFT_ON)) {
groupNavigationDirection = View.FOCUS_BACKWARD;
}
}
// If a modifier is held, try to interpret the key as a shortcut.
if (event.getAction() == KeyEvent.ACTION_DOWN
&& !KeyEvent.metaStateHasNoModifiers(event.getMetaState())
&& event.getRepeatCount() == 0
&& !KeyEvent.isModifierKey(event.getKeyCode())
&& groupNavigationDirection == 0) {
if (mView.dispatchKeyShortcutEvent(event)) {
return FINISH_HANDLED;
}
if (shouldDropInputEvent(q)) {
return FINISH_NOT_HANDLED;
}
}
// Apply the fallback event policy.
if (mFallbackEventHandler.dispatchKeyEvent(event)) {
return FINISH_HANDLED;
}
if (shouldDropInputEvent(q)) {
return FINISH_NOT_HANDLED;
}
// Handle automatic focus changes.
//如果是按键按下事件，则处理焦点自动导航
if (event.getAction() == KeyEvent.ACTION_DOWN) {
if (groupNavigationDirection != 0) {
if (performKeyboardGroupNavigation(groupNavigationDirection)) {
return FINISH_HANDLED;
}
} else {
//执行焦点导航逻辑
if (performFocusNavigation(event)) {
return FINISH_HANDLED;
}
}
}
return FORWARD;
}
二、dispatchKeyEvent(KeyEvent event) 在DecorView、ViewGroup、View中的分发流程
1、DecorView.java
DecorView.java
@Override
public boolean dispatchKeyEvent(KeyEvent event) {
final int keyCode = event.getKeyCode();
final int action = event.getAction();
final boolean isDown = action == KeyEvent.ACTION_DOWN;
if (isDown && (event.getRepeatCount() == 0)) {
// First handle chording of panel key: if a panel key is held
// but not released, try to execute a shortcut in it.
if ((mWindow.mPanelChordingKey > 0) && (mWindow.mPanelChordingKey != keyCode)) {
boolean handled = dispatchKeyShortcutEvent(event);
if (handled) {
return true;
}
}
// If a panel is open, perform a shortcut on it without the
// chorded panel key
if ((mWindow.mPreparedPanel != null) && mWindow.mPreparedPanel.isOpen) {
if (mWindow.performPanelShortcut(mWindow.mPreparedPanel, keyCode, event, 0)) {
return true;
}
}
}
if (!mWindow.isDestroyed()) {
//DecorView中的mWindow唯一实现类就是PhoneWindow，而Activity则是Window.Callback是实现类。Activity中调用mWindow.setCallback(this)
//故而，此处mWindow.getCallback()获取到的就是Activity实例，调用cb.dispatchKeyEvent(event)实际上就是调用到Activity.dispatchKeyEvent(event)
//Activity会在其dispatchKeyEvent(event)方法中做一些按键事件分发处理。如onKeyDown、onKeyUp、onKeyLongPress、onKeyMultiple方法的回调
//这些回调方法中，如果消费了事件，则返回true，结束事件继续分发；如果不消费事件，则返回false，继续调用父类super.dispatchKeyEvent(event)方法层层递归进行事件分发
final Window.Callback cb = mWindow.getCallback();
final boolean handled = cb != null && mFeatureId < 0 ? cb.dispatchKeyEvent(event)
: super.dispatchKeyEvent(event);
if (handled) {
return true;
}
}
return isDown ? mWindow.onKeyDown(mFeatureId, event.getKeyCode(), event)
: mWindow.onKeyUp(mFeatureId, event.getKeyCode(), event);
}
2、Activity.java
Activity.java
/**
* Called to process key events. You can override this to intercept all
* key events before they are dispatched to the window. Be sure to call
* this implementation for key events that should be handled normally.
*
* @param event The key event.
*
* @return boolean Return true if this event was consumed.
*/
public boolean dispatchKeyEvent(KeyEvent event) {
onUserInteraction();
// Let action bars open menus in response to the menu key prioritized over
// the window handling it
final int keyCode = event.getKeyCode();
if (keyCode == KeyEvent.KEYCODE_MENU &&
mActionBar != null && mActionBar.onMenuKeyEvent(event)) {
return true;
}
Window win = getWindow();
if (win.superDispatchKeyEvent(event)) {
return true;
}
View decor = mDecor;
if (decor == null) decor = win.getDecorView();
//调用KeyEvent event对象的dispatch(Callback receiver, DispatcherState state,Object target)方法
//把事件接收的处理者作为reciver传入，进行事件的处理。例如，调用事件接收者的onKeyDown、onKeyUp、onKeyLongPress、onKeyMultiple方法的回调
//事件处理的结果会向上层回传给DecorView.dispatchKeyEvent()-->mView.dispatchKeyEvent(event)
// 如果返回true，则消费事件，直接将结果回传到ViewRootImpl中的mView.dispatchKeyEvent(event)；
// 如果返回false，则DecorView会调用super.dispatchKeyEvent(event)层层递归分发事件直到返回结果。
//
return event.dispatch(this, decor != null
? decor.getKeyDispatcherState() : null, this);
}
3、ViewGroup.java
ViewGroup.java
@Override
public boolean dispatchKeyEvent(KeyEvent event) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onKeyEvent(event, 1);
}
if ((mPrivateFlags & (PFLAG_FOCUSED | PFLAG_HAS_BOUNDS))
== (PFLAG_FOCUSED | PFLAG_HAS_BOUNDS)) {
if (super.dispatchKeyEvent(event)) {
return true;
}
} else if (mFocused != null && (mFocused.mPrivateFlags & PFLAG_HAS_BOUNDS)
== PFLAG_HAS_BOUNDS) {
//调用当前获得焦点或包含焦点的mFocused.dispatchKeyEvent(event)
if (mFocused.dispatchKeyEvent(event)) {
//如何当前焦点view消费了该事件，则返回true，结束事件分发后续流程。
return true;
}
}
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 1);
}
return false;
}
4、View.java
View.java
/**
* Dispatch a key event to the next view on the focus path. This path runs
* from the top of the view tree down to the currently focused view. If this
* view has focus, it will dispatch to itself. Otherwise it will dispatch
* the next node down the focus path. This method also fires any key
* listeners.
*
* @param event The key event to be dispatched.
* @return True if the event was handled, false otherwise.
*/
public boolean dispatchKeyEvent(KeyEvent event) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onKeyEvent(event, 0);
}
// Give any attached key listener a first crack at the event.
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
//如果有设置按键监听事件，则优先将事件交给监听器处理。如果监听器不消费事件，则继续往下执行后续流程
if (li != null && li.mOnKeyListener != null && (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnKeyListener.onKey(this, event.getKeyCode(), event)) {
return true;
}
//将view自己作为事件接收者，传入KeyEvent event对象，处理事件的分发
if (event.dispatch(this, mAttachInfo != null
? mAttachInfo.mKeyDispatchState : null, this)) {
//如果事件被消费掉了，则返回true，直接返回到上层mView.dispatchKeyEvent(event)结束事件传递
return true;
}
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
//如事件没有被消费掉，返回false
return false;
}
三、KeyEvent中dispatch(Callback receiver, DispatcherState state,Object target)如果将事件分发给接收者receiver中的各个回调方法
通过该方法，接收器receiver的onKeyDown、onKeyUp、onKeyLongPress、onKeyMultiple等方法将被回调。
/**
* Deliver this key event to a {@link Callback} interface. If this is
* an ACTION_MULTIPLE event and it is not handled, then an attempt will
* be made to deliver a single normal event.
*
* @param receiver The Callback that will be given the event.
* @param state State information retained across events.
* @param target The target of the dispatch, for use in tracking.
*
* @return The return value from the Callback method that was called.
*/
public final boolean dispatch(Callback receiver, DispatcherState state,
Object target) {
switch (mAction) {
case ACTION_DOWN: {
mFlags &= ~FLAG_START_TRACKING;
if (DEBUG) Log.v(TAG, "Key down to " + target + " in " + state
+ ": " + this);
boolean res = receiver.onKeyDown(mKeyCode, this);
if (state != null) {
if (res && mRepeatCount == 0 && (mFlags&FLAG_START_TRACKING) != 0) {
if (DEBUG) Log.v(TAG, " Start tracking!");
state.startTracking(this, target);
} else if (isLongPress() && state.isTracking(this)) {
try {
if (receiver.onKeyLongPress(mKeyCode, this)) {
if (DEBUG) Log.v(TAG, " Clear from long press!");
state.performedLongPress(this);
res = true;
}
} catch (AbstractMethodError e) {
}
}
}
return res;
}
case ACTION_UP:
if (DEBUG) Log.v(TAG, "Key up to " + target + " in " + state
+ ": " + this);
if (state != null) {
state.handleUpEvent(this);
}
return receiver.onKeyUp(mKeyCode, this);
case ACTION_MULTIPLE:
final int count = mRepeatCount;
final int code = mKeyCode;
if (receiver.onKeyMultiple(code, count, this)) {
return true;
}
if (code != KeyEvent.KEYCODE_UNKNOWN) {
mAction = ACTION_DOWN;
mRepeatCount = 0;
boolean handled = receiver.onKeyDown(code, this);
if (handled) {
mAction = ACTION_UP;
receiver.onKeyUp(code, this);
}
mAction = ACTION_MULTIPLE;
mRepeatCount = count;
return handled;
}
return false;
}
return false;
}
三、焦点导航
在上述按键事件的入口中提到的ViewRootImpl中
//分发按键事件到视图树，mView即是DecorView
//DecorView继承FrameLayout,FrameLayout继承ViewGroup，
// DecorView.dispatchKeyEvent(event)重写了父类ViewGroup.dispatchKeyEvent(event)方法
// Deliver the key to the view hierarchy.
if (mView.dispatchKeyEvent(event)) {
return FINISH_HANDLED;
}
....
// Handle automatic focus changes.
//如果是按键按下事件，则处理焦点自动导航
if (event.getAction() == KeyEvent.ACTION_DOWN) {
if (groupNavigationDirection != 0) {
if (performKeyboardGroupNavigation(groupNavigationDirection)) {
return FINISH_HANDLED;
}
} else {
//执行焦点导航逻辑
if (performFocusNavigation(event)) {
return FINISH_HANDLED;
}
}
}
如果mView.dispatchKeyEvent(event)返回true，则结束事件分发；
如果返回false，则调用如下方法
//执行焦点导航逻辑
if (performFocusNavigation(event)) {
return FINISH_HANDLED;
}
继续执行后续的焦点导航流程。
焦点导航的总体流程就是：
1、View focused = mView.findFocus();//从视图树的顶层，即DecorView一层一层的递归查找当前获得焦点的view
2、View v = focused.focusSearch(direction);根据导航的方向查找下一个可获取焦点的view
3、v.requestFocus(direction, mTempRect)请求获取焦点
4、v.requestFocus(direction,mTempRect)内部，调用mParent.requestChildFocus(this, focused)逐层递归向上级通知
ViewRootImpl.java
/**
* 系统焦点自动导航逻辑
* 注意：以下所有的焦点导航逻辑都是在KeyEvent.ACTION_DOWN下执行
* **/
private boolean performFocusNavigation(KeyEvent event) {
int direction = 0;
switch (event.getKeyCode()) {
//左方向键
case KeyEvent.KEYCODE_DPAD_LEFT:
if (event.hasNoModifiers()) {
direction = View.FOCUS_LEFT;
}
break;
//右方向键
case KeyEvent.KEYCODE_DPAD_RIGHT:
if (event.hasNoModifiers()) {
direction = View.FOCUS_RIGHT;
}
break;
//上方向键
case KeyEvent.KEYCODE_DPAD_UP:
if (event.hasNoModifiers()) {
direction = View.FOCUS_UP;
}
break;
//下方向键
case KeyEvent.KEYCODE_DPAD_DOWN:
if (event.hasNoModifiers()) {
direction = View.FOCUS_DOWN;
}
break;
//TAB键
case KeyEvent.KEYCODE_TAB:
if (event.hasNoModifiers()) {
direction = View.FOCUS_FORWARD;
} else if (event.hasModifiers(KeyEvent.META_SHIFT_ON)) {
direction = View.FOCUS_BACKWARD;
}
break;
}
if (direction != 0) {
//mView:即DecorView,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.
View focused = mView.findFocus();//从视图树的顶层，即DecorView一层一层的递归查找当前获得焦点的view
if (focused != null) {
//找到了当前获得焦点的focused,调用该焦点view的focusSearch(direction)方法查找direction方向上下一个将要获取焦点的view
//focused.focusSearch(direction)实际上会调用mParent.focusSearch(this, direction)方法，层层递归，直到调用到DecorView的focusSearch(this, direction)方法。
//而DecorView继承ViewGroup，实际上最终会调用到FocusFinder.getInstance().findNextFocus(this, focused, direction)，this 就是DecorView对象
View v = focused.focusSearch(direction);
if (v != null && v != focused) {//找到下一个可获取焦点view，并且不是当前获取焦点的view
// do the math the get the interesting rect
// of previous focused into the coord system of
// newly focused view
focused.getFocusedRect(mTempRect);
if (mView instanceof ViewGroup) {
((ViewGroup) mView).offsetDescendantRectToMyCoords(
focused, mTempRect);
((ViewGroup) mView).offsetRectIntoDescendantCoords(
v, mTempRect);
}
//让找到的下一个可获取焦点的view获取焦点
//该v可能是view或者是ViewGroup。 ViewGroup获取焦点的最大区别就是重写了View.requestFocus(int direction, Rect previouslyFocusedRect)方法。
//ViewGroup会根据指定的焦点策略（FOCUS_BEFORE_DESCENDANTS、FOCUS_AFTER_DESCENDANTS、FOCUS_BLOCK_DESCENDANTS）来处理焦点在自己和子View之间的流转。
if (v.requestFocus(direction, mTempRect)) {//获取到焦点后，该焦点view会层层上报自己的parent，让parent做出相应的响应
//播放声音
playSoundEffect(SoundEffectConstants
.getContantForFocusDirection(direction));
//新的view已经获取到了焦点，返回true消费事件，事件不再往下继续执行。
return true;
}
}
// Give the focused view a last chance to handle the dpad key.
//给当前获取焦点的focused view 最后一次处理事件的机会
//即，focused.focusSearch(direction)查找的下个可获取焦点的view 为null时 获取前面的事件未被消费调，会获得执行机会
if (mView.dispatchUnhandledMove(focused, direction)) {
//从DecorView开始，递归调用dispatchUnhandledMove(focused, direction),直到focused中的dispatchUnhandledMove(focused, direction)
return true;
}
} else {
//递归调用，重置默认焦点（整个视图树上只能有唯一一个默认焦点view）
if (mView.restoreDefaultFocus()) {
return true;
}
}
}
return false;
}
1、获取当前获得焦点view
mView即DecorView,从DecorView开始，一层一层的向下递归查找当前获得焦点的view
View focused = mView.findFocus()
2、搜索下一个在指定方向上可获取焦点的view
找到了当前获得焦点的focused,调用该焦点view的focusSearch(direction)方法查找direction方向上下一个将要获取焦点的view。
focused.focusSearch(direction)实际上会调用mParent.focusSearch(this, direction)方法，层层递归，直到调用到DecorView的focusSearch(this, direction)方法。
而DecorView继承ViewGroup，实际上最终会调用到FocusFinder.getInstance().findNextFocus(this, focused, direction)，this 就是DecorView对象。
View v = focused.focusSearch(direction)
最终会调用到DecorView父类ViewGroup中的FocusFinder.getInstance().findNextFocus(this, focused, direction);
ViewGroup.java
ViewGroup.java
/**
* Find the nearest view in the specified direction that wants to take
* focus.
*
* @param focused The view that currently has focus
* @param direction One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, and
* FOCUS_RIGHT, or 0 for not applicable.
*/
@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;
}
FocusFinder.java
FocusFinder.java
/**
* 在指定的root ViewGroup上，更加当前传入的获得焦点的view，查找direction方向上可获取焦点的下一个view。
*
* root 如果是DecoverView,则是在整个视图树中查找；root 如果是其它ViewGroup，则是在该ViewGroup上查找；
*
* 即 root，限定的焦点在视图树上查找的范围。
*
* Find the next view to take focus in root's descendants, starting from the view
* that currently is focused.
* @param root Contains focused. Cannot be null.
* @param focused Has focus now. 当前获取焦点的view
* @param direction Direction to look. 查找的方向
* @return The next focusable view, or null if none exists.
*/
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;
ViewGroup effectiveRoot = getEffectiveRoot(root, focused);
if (focused != null) {
//优先查找用户指定的下一个可获取焦点的view
//即用户在XML中或代码中指定的下一个获取焦点view的ID值来查找
next = findNextUserSpecifiedFocus(effectiveRoot, focused, direction);
}
if (next != null) {
//如果找到用户指定的获取下一个焦点的view，则直接返回
return next;
}
ArrayList<View> focusables = mTempList;
try {
focusables.clear();
//添加effectiveRoot下的所有view到focusables集合中去
//重写ViewGroup的该方法，可以实现焦点记忆功能
effectiveRoot.addFocusables(focusables, direction);
if (!focusables.isEmpty()) {
//根据系统默认的就近原则算法，查找下一个direction方向上可获取焦点的最近的view
next = findNextFocus(effectiveRoot, focused, focusedRect, direction, focusables);
}
} finally {
focusables.clear();
}
return next;
}
3、请求获取焦点
搜索到下一个获取焦点的view后，调用该view.requestFocus(direction, mTempRect)方法
注意:调用requestFocus(direction, mTempRect)需要区分调用者。
如果是ViewGroup，则会更加焦点获取策略，实现父View和子View之间获取焦点的优先级。
如下是ViewGroup.java 和View.java 中requestFocus方法是实现：
ViewGroup.java
ViewGroup.java
/**
* {@inheritDoc}
*
* ViewGroup请求焦点的方法
*
* ViewGroup重新了View的该方法，实现了获取焦点顺序的拦截。可根据不同的策略，实现父View和子View之间获取焦点的优先级。
* <p>
* 通过FOCUS_BEFORE_DESCENDANTS，父View优先获取焦点，配合重写addFocusables（）方法，实现焦点记忆功能
* <p>
* Looks for a view to give focus to respecting the setting specified by
* {@link #getDescendantFocusability()}.
* <p>
* Uses {@link #onRequestFocusInDescendants(int, android.graphics.Rect)} to
* find focus within the children of this group when appropriate.
*
* @see #FOCUS_BEFORE_DESCENDANTS
* @see #FOCUS_AFTER_DESCENDANTS
* @see #FOCUS_BLOCK_DESCENDANTS
* @see #onRequestFocusInDescendants(int, android.graphics.Rect)
*/
@Override
public boolean requestFocus(int direction, Rect previouslyFocusedRect) {
if (DBG) {
System.out.println(this + " ViewGroup.requestFocus direction="
+ direction);
}
int descendantFocusability = getDescendantFocusability();
//以下代码如果是调用super.requestFocus(direction, previouslyFocusedRect)，表示viewGroup自己处理焦点事件
boolean result;
switch (descendantFocusability) {
//直接阻止后代获取焦点，自己处理请求焦点的逻辑
case FOCUS_BLOCK_DESCENDANTS:
result = super.requestFocus(direction, previouslyFocusedRect);
break;
//可优先于后代获取焦点，自己不处理时才交给后代处理
case FOCUS_BEFORE_DESCENDANTS: {
final boolean took = super.requestFocus(direction, previouslyFocusedRect);
result = took ? took : onRequestFocusInDescendants(direction,
previouslyFocusedRect);
break;
}
//将获取焦点的权利优先交给后代，后代都不消费时，自己在处理
case FOCUS_AFTER_DESCENDANTS: {
final boolean took = onRequestFocusInDescendants(direction, previouslyFocusedRect);
result = took ? took : super.requestFocus(direction, previouslyFocusedRect);
break;
}
default:
throw new IllegalStateException(
"descendant focusability must be one of FOCUS_BEFORE_DESCENDANTS,"
+ " FOCUS_AFTER_DESCENDANTS, FOCUS_BLOCK_DESCENDANTS but is "
+ descendantFocusability);
}
if (result && !isLayoutValid() && ((mPrivateFlags & PFLAG_WANTS_FOCUS) == 0)) {
mPrivateFlags |= PFLAG_WANTS_FOCUS;
}
return result;
}
View.java
View.java
public boolean requestFocus(int direction, Rect previouslyFocusedRect) {
return requestFocusNoSearch(direction, previouslyFocusedRect);
}
//直接请求获取焦点，不再搜索
private boolean requestFocusNoSearch(int direction, Rect previouslyFocusedRect) {
//在该方法中会对控件的当前状态进行判断, 如果不符合获取焦点的前提则直接返回false告知调用方, 控件不会获取焦点
//只要符合前提就会继续执行, 最终必定返回true, 不论当前控件的焦点状态是否有改变
// need to be focusable
if (!canTakeFocus()) {
return false;
}
// need to be focusable in touch mode if in touch mode
if (isInTouchMode() &&
(FOCUSABLE_IN_TOUCH_MODE != (mViewFlags & FOCUSABLE_IN_TOUCH_MODE))) {
return false;
}
// need to not have any parents blocking us
//如果该View的父View阻止其获取焦点，则直接返回false
if (hasAncestorThatBlocksDescendantFocus()) {
return false;
}
if (!isLayoutValid()) {
mPrivateFlags |= PFLAG_WANTS_FOCUS;
} else {
clearParentsWantFocus();
}
//framework内部处理获得焦点核心
handleFocusGainInternal(direction, previouslyFocusedRect);
return true;
}
/**
*
* framework处理获取焦点的内部核心逻辑
* Give this view focus. This will cause
* {@link #onFocusChanged(boolean, int, android.graphics.Rect)} to be called.
*
* Note: this does not check whether this {@link View} should get focus, it just
* gives it focus no matter what. It should only be called internally by framework
* code that knows what it is doing, namely {@link #requestFocus(int, Rect)}.
*
* @param direction values are {@link View#FOCUS_UP}, {@link View#FOCUS_DOWN},
* {@link View#FOCUS_LEFT} or {@link View#FOCUS_RIGHT}. This is the direction which
* focus moved when requestFocus() is called. It may not always
* apply, in which case use the default View.FOCUS_DOWN.
* @param previouslyFocusedRect The rectangle of the view that had focus
* prior in this View's coordinate system.
*/
void handleFocusGainInternal(@FocusRealDirection int direction, Rect previouslyFocusedRect) {
if (DBG) {
System.out.println(this + " requestFocus()");
}
if ((mPrivateFlags & PFLAG_FOCUSED) == 0) {
mPrivateFlags |= PFLAG_FOCUSED;
//getRootView() 获取到的是DecorView，即在整个视图树中查找当前已经获取焦点的view
View oldFocus = (mAttachInfo != null) ? getRootView().findFocus() : null;
if (mParent != null) {
//层层向上递归，通知父view 我获取了焦点
mParent.requestChildFocus(this, this);
updateFocusedInCluster(oldFocus, direction);
}
if (mAttachInfo != null) {
//通知View树上焦点全局监听者
mAttachInfo.mTreeObserver.dispatchOnGlobalFocusChange(oldFocus, this);
}
//通知view自己获得焦点，重写该方法，可监听view自己焦点状态变更
onFocusChanged(true, direction, previouslyFocusedRect);
//刷新view drawable状态
refreshDrawableState();
}
}
4、焦点变更逐层递归向上级通知
View获取到焦点后，会调用mParent.requestChildFocus(this, focused)逐层递归向上级通知
ViewGroup.java
@Override
public void requestChildFocus(View child, View focused) {
//如果入参 child==focused 为true，即代表 this 是focused 的直接父view
if (DBG) {
System.out.println(this + " requestChildFocus()");
}
if (getDescendantFocusability() == FOCUS_BLOCK_DESCENDANTS) {
return;
}
// Unfocus us, if necessary
//如果有必要，清除焦点
super.unFocus(focused);
// We had a previous notion of who had focus. Clear it.
if (mFocused != child) {
if (mFocused != null) {
//如果之前有view获取焦点，取消焦点
mFocused.unFocus(focused);
}
//记录获得焦点的view或包含焦点的viewGroup
mFocused = child;
}
if (mParent != null) {
//层层向上递归，通知父view，我的子view获取了焦点
//如果入参 child==focused 为true，即代表 this 是focused 的直接父view
mParent.requestChildFocus(this, focused);
}
}
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