刚接触Android开发的时候，对touch、key事件的处理总是一知半解，一会是Activity里的方法，一会是各种View
中的，自己始终不清楚到底哪个在先哪个在后，总之对整个处理流程没能很好的把握。每次写这部分代码的时候都有些心虚，
因为我不是很清楚什么时候、以什么样的顺序被调用，大都是打下log看看，没问题就算ok了。但随着时间流逝，这种感觉一直
折磨着我。期间也在网上搜索了相关资料，但总感觉不是那么令人满意。自打开始研究Android源码起，这部分内容的分析早就
被列在我的TODO list上了。因为弄懂这部分处理逻辑对明明白白地写android程序实在是太重要了，所以今天我就带领大家看看
这部分的处理逻辑。touch事件的处理我将放在另一篇博客中介绍（相比KeyEvent，大体都一样，只是稍微复杂些）。
为了突出本文的重点，我们直接从事件被派发到View层次结构的根节点DecorView开始分析，这里我们先来看看DecorView#
dispatchKeyEvent方法，代码如下：
@Override public boolean dispatchKeyEvent(KeyEvent event) { final int keyCode = event.getKeyCode(); final int action = event.getAction(); final boolean isDown = action == KeyEvent.ACTION_DOWN; /// 1. 第一次down事件的时候，处理panel的快捷键 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 ((mPanelChordingKey > 0) && (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 ((mPreparedPanel != null) && mPreparedPanel.isOpen) { if (performPanelShortcut(mPreparedPanel, keyCode, event, 0)) { return true; } } } /// 2. 这里是我们本文的重点，当window没destroy且其Callback非空的话，交给其Callback处理 if (!isDestroyed()) { // Activity、Dialog都是Callback接口的实现 final Callback cb = getCallback(); // mFeatureId < 0 表示是application的DecorView，比如Activity、Dialog final boolean handled = cb != null && mFeatureId < 0 ? cb.dispatchKeyEvent(event) // 派发给callback的方法 : super.dispatchKeyEvent(event); // 否则直接派发到ViewGroup#dispatchKeyEvent（View层次结构） if (handled) { return true; // 如果被上面的步骤处理了则直接返回true，不再往下传递 } } /// 3. 这是key事件的最后一步，如果到这一步还没处理掉，则派发到PhoneWindow对应的onKeyDown, onKeyUp方法 return isDown ? PhoneWindow.this.onKeyDown(mFeatureId, event.getKeyCode(), event) : PhoneWindow.this.onKeyUp(mFeatureId, event.getKeyCode(), event); }
接下来我们按照这个派发顺序依次来看看相关方法的实现，这里先看看Activity(Callback)的dispatchKeyEvent实现：
/** * 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. */ @Override public boolean dispatchKeyEvent(KeyEvent event) { /// 2.1. 回调接口，实际开发中用处不大，你感兴趣可以参看其方法doc onUserInteraction(); Window win = getWindow(); /// 2.2. 从这里事件的处理交给了与之相关的window对象，实质是派发到了view层次结构 if (win.superDispatchKeyEvent(event)) { return true; // 被view层次结构处理掉了则直接返回true } View decor = mDecor; if (decor == null) decor = win.getDecorView(); /// 2.3. 到这里如果view层次结构没处理则交给KeyEvent本身的dispatch方法，Activity的各种回调方法会被触发 return event.dispatch(this, decor != null ? decor.getKeyDispatcherState() : null, this); }
紧接着我们看看，Window#superDispatchKeyEvent方法，相关代码如下：
<!-- Window.java -->
/**
* Used by custom windows, such as Dialog, to pass the key press event
* further down the view hierarchy. Application developers should
* not need to implement or call this.
*
*/
public abstract boolean superDispatchKeyEvent(KeyEvent event);
<!-- PhoneWindow.java -->
@Override
public boolean superDispatchKeyEvent(KeyEvent event) {
return mDecor.superDispatchKeyEvent(event);
}
<!-- DecorView.superDispatchKeyEvent -->
public boolean superDispatchKeyEvent(KeyEvent event) {
/// 2.2.1. 进入view层次结构了，即调用ViewGroup的对应实现了。。。
if (super.dispatchKeyEvent(event)) {
return true; // 如果被view层次结构处理了则直接返回true。
}
// Not handled by the view hierarchy, does the action bar want it
// to cancel out of something special?
/// 2.2.2. ActionBar对BACK key的特殊处理
if (event.getKeyCode() == KeyEvent.KEYCODE_BACK) {
final int action = event.getAction();
// Back cancels action modes first.
if (mActionMode != null) {
if (action == KeyEvent.ACTION_UP) {
mActionMode.finish();
}
return true;
}
// Next collapse any expanded action views.
if (mActionBar != null && mActionBar.hasExpandedActionView()) {
if (action == KeyEvent.ACTION_UP) {
mActionBar.collapseActionView();
}
return true;
}
}
/// 2.2.3. 最后返回false表示没处理掉，会接着2.3.步骤处理
return false;
}
然后我们接着看看2.2.1.包括的小步骤，即ViewGroup#dispatchKeyEvent的实现，代码如下：
@Override public boolean dispatchKeyEvent(KeyEvent event) { /// 2.2.1.1. KeyEvent一致性检测用的，可忽略。。。 if (mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onKeyEvent(event, 1); } if ((mPrivateFlags & (PFLAG_FOCUSED | PFLAG_HAS_BOUNDS)) == (PFLAG_FOCUSED | PFLAG_HAS_BOUNDS)) { /// 2.2.1.2. 如果此ViewGroup是focused或者具体的大小被设置了（有边界），则交给它处理，即调用View的实现 if (super.dispatchKeyEvent(event)) {// super即View的实现 return true; } } else if (mFocused != null && (mFocused.mPrivateFlags & PFLAG_HAS_BOUNDS) == PFLAG_HAS_BOUNDS) { /// 2.2.1.3. 否则，如果此ViewGroup中有focused的child，且child有具体的大小，则交给mFocused处理 if (mFocused.dispatchKeyEvent(event)) { // 注意这里可能是个递归调用 return true; // 我们可以看到并不是每个child都能响应key事件，前提必须是focused child才有机会响应 } } if (mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onUnhandledEvent(event, 1); } /// 2.2.1.4. 最后都没被处理返回false，2.2.2.步骤会接着执行。。。 return false; }
这里我们可以看出对KeyEvent来说在View层次结构中，如果ViewGroup条件满足则会优先处理事件而不是先派发给其孩子view，
这一点和touch事件有所不同。这里我们看看View的dispatchKeyEvent实现：
/** * 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; /// 2.2.1.2(3).1. 调用onKeyListener，如果它非空且view是ENABLED状态，监听器优先触发 if (li != null && li.mOnKeyListener != null && (mViewFlags & ENABLED_MASK) == ENABLED && li.mOnKeyListener.onKey(this, event.getKeyCode(), event)) { return true; } /// 2.2.1.2(3).2. 调用KeyEvent.dispatch方法，并将view对象本身作为参数传递进去，view的各种callback方法在这里被触发 if (event.dispatch(this, mAttachInfo != null ? mAttachInfo.mKeyDispatchState : null, this)) { return true; } if (mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onUnhandledEvent(event, 0); } /// 2.2.1.2(3).3. 还没处理掉返回false，接着2.2.1.4.执行 return false; }
这里关于View和ViewGroup的dispatchKeyEvent方法我们多说几句。这2个方法一起就实现了view层次结构按照focus路线从上到下
派发KeyEvent的整个流程，后面我会专门用一篇文章来详解下ViewGroup里mFocused变量和View里focus变化的处理过程。
言归正传，不管是这里的2.2.1.2(3).2.步骤还是前面Activity里的2.3.步骤，都调到了KeyEvent.dispatch方法，不过在看其代码之前我们
先来看看这里用到的mAttachInfo.mKeyDispatchState对象是咋来的，代码如下：
// 这句代码位于View.AttachInfo类里 final KeyEvent.DispatcherState mKeyDispatchState = new KeyEvent.DispatcherState(); /** * Return the global {@link KeyEvent.DispatcherState KeyEvent.DispatcherState} * for this view's window. Returns null if the view is not currently attached * to the window. Normally you will not need to use this directly, but * just use the standard high-level event callbacks like * {@link #onKeyDown(int, KeyEvent)}. */ public KeyEvent.DispatcherState getKeyDispatcherState() { return mAttachInfo != null ? mAttachInfo.mKeyDispatchState : null; } // KeyEvent.DispatcherState类 /** * Use with {@link KeyEvent#dispatch(Callback, DispatcherState, Object)} * for more advanced key dispatching, such as long presses. */ public static class DispatcherState { int mDownKeyCode; Object mDownTarget; SparseIntArray mActiveLongPresses = new SparseIntArray(); /** * Reset back to initial state. */ public void reset() { // 清空内部状态 if (DEBUG) Log.v(TAG, "Reset: " + this); mDownKeyCode = 0; mDownTarget = null; mActiveLongPresses.clear(); } /** * Stop any tracking associated with this target. */ public void reset(Object target) { // 清空target对应的内部状态 if (mDownTarget == target) { // 只有相同时才清空，否则啥也不做 if (DEBUG) Log.v(TAG, "Reset in " + target + ": " + this); mDownKeyCode = 0; mDownTarget = null; } } /** * Start tracking the key code associated with the given event. This * can only be called on a key down. It will allow you to see any * long press associated with the key, and will result in * {@link KeyEvent#isTracking} return true on the long press and up * events. * * <p>This is only needed if you are directly dispatching events, rather * than handling them in {@link Callback#onKeyDown}. */ public void startTracking(KeyEvent event, Object target) { if (event.getAction() != ACTION_DOWN) { // 状态检测 throw new IllegalArgumentException( "Can only start tracking on a down event"); } if (DEBUG) Log.v(TAG, "Start trackingt in " + target + ": " + this); mDownKeyCode = event.getKeyCode(); // 赋值，表示正在track某个keycode mDownTarget = target; } /** * Return true if the key event is for a key code that is currently * being tracked by the dispatcher. */ public boolean isTracking(KeyEvent event) { return mDownKeyCode == event.getKeyCode(); } /** * Keep track of the given event's key code as having performed an * action with a long press, so no action should occur on the up. * <p>This is only needed if you are directly dispatching events, rather * than handling them in {@link Callback#onKeyLongPress}. */ public void performedLongPress(KeyEvent event) {// 用来记录发生了生理长按事件 mActiveLongPresses.put(event.getKeyCode(), 1); } /** * Handle key up event to stop tracking. This resets the dispatcher state, * and updates the key event state based on it. * <p>This is only needed if you are directly dispatching events, rather * than handling them in {@link Callback#onKeyUp}. */ public void handleUpEvent(KeyEvent event) { final int keyCode = event.getKeyCode(); if (DEBUG) Log.v(TAG, "Handle key up " + event + ": " + this); int index = mActiveLongPresses.indexOfKey(keyCode); if (index >= 0) { // 如果发生过生理长按则设置event.mFlags为CACELED，这样在接下来的receiver.onKeyUp中有些处理就不会发生了 if (DEBUG) Log.v(TAG, " Index: " + index); // 因为事件被标记为CANCELED了 event.mFlags |= FLAG_CANCELED | FLAG_CANCELED_LONG_PRESS; mActiveLongPresses.removeAt(index); } if (mDownKeyCode == keyCode) { if (DEBUG) Log.v(TAG, " Tracking!"); event.mFlags |= FLAG_TRACKING; // 设置event正确的mFlags，接下来的receiver.onKeyUp可能会检测此状态 mDownKeyCode = 0; // reset，表示此keycode的tracking到此结束了 mDownTarget = null; } } }
大概了解了KeyEvent.DispatcherState类，我们就可以来看看KeyEvent.dispatch方法了，代码如下：
/** * 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: { // DOWN事件 mFlags &= ~FLAG_START_TRACKING; //先清掉START_TRACKING标记 if (DEBUG) Log.v(TAG, "Key down to " + target + " in " + state + ": " + this); boolean res = receiver.onKeyDown(mKeyCode, this); // 回调Callback接口的onKeyDown方法，View和Activity都是此接口的实现者 if (state != null) { // 一般都成立 if (res && mRepeatCount == 0 && (mFlags&FLAG_START_TRACKING) != 0) { if (DEBUG) Log.v(TAG, " Start tracking!"); // receiver.onKeyDown返回true了且不是repeated state.startTracking(this, target); // 并且也没有开始tracking，则开始tracking当前的KeyEvent和target } else if (isLongPress() && state.isTracking(this)) { // 处理生理长按 try { // 检测到生理长按则调用receiver.onKeyLongPress方法 if (receiver.onKeyLongPress(mKeyCode, this)) { if (DEBUG) Log.v(TAG, " Clear from long press!"); state.performedLongPress(this); // 记录此event已经有生理long press发生了。。。 res = true; // 设置为处理了 } } catch (AbstractMethodError e) { } } } return res; // 返回down事件处理的结果 } case ACTION_UP: // UP事件 if (DEBUG) Log.v(TAG, "Key up to " + target + " in " + state + ": " + this); if (state != null) { state.handleUpEvent(this); // reset state的内部状态，也改变了KeyEvent的某些状态 } return receiver.onKeyUp(mKeyCode, this); // 最后调用receiver.onKeyUp方法 case ACTION_MULTIPLE: // 这里可以忽略掉 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; }
看完了KeyEvent的具体实现，我们接着看看receiver（Callback接口）的onKeyDown、onKeyUp实现，先来看View相关的，代码如下：
/** * Default implementation of {@link KeyEvent.Callback#onKeyDown(int, KeyEvent) * KeyEvent.Callback.onKeyDown()}: perform press of the view * when {@link KeyEvent#KEYCODE_DPAD_CENTER} or {@link KeyEvent#KEYCODE_ENTER} * is released, if the view is enabled and clickable. * * <p>Key presses in software keyboards will generally NOT trigger this listener, * although some may elect to do so in some situations. Do not rely on this to * catch software key presses. * * @param keyCode A key code that represents the button pressed, from * {@link android.view.KeyEvent}. * @param event The KeyEvent object that defines the button action. */ public boolean onKeyDown(int keyCode, KeyEvent event) { boolean result = false; if (KeyEvent.isConfirmKey(keyCode)) { // 只处理KEYCODE_DPAD_CENTER、KEYCODE_ENTER这2个按键 if ((mViewFlags & ENABLED_MASK) == DISABLED) { return true; // 针对disabled View直接返回true表示处理过了 } // Long clickable items don't necessarily have to be clickable if (((mViewFlags & CLICKABLE) == CLICKABLE || (mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) && (event.getRepeatCount() == 0)) { // clickable或者long_clickable且是第一次down事件 setPressed(true); // 标记pressed，你可能设置了View不同的background，这时候就会有所体现（比如高亮效果） checkForLongClick(0); // 启动View的long click检测 return true; // 到达这一步就表示KeyEvent被处理掉了 } } return result; } /** * Default implementation of {@link KeyEvent.Callback#onKeyUp(int, KeyEvent) * KeyEvent.Callback.onKeyUp()}: perform clicking of the view * when {@link KeyEvent#KEYCODE_DPAD_CENTER} or * {@link KeyEvent#KEYCODE_ENTER} is released. * <p>Key presses in software keyboards will generally NOT trigger this listener, * although some may elect to do so in some situations. Do not rely on this to * catch software key presses. * * @param keyCode A key code that represents the button pressed, from * {@link android.view.KeyEvent}. * @param event The KeyEvent object that defines the button action. */ public boolean onKeyUp(int keyCode, KeyEvent event) { if (KeyEvent.isConfirmKey(keyCode)) { // 同onKeyDown，默认也只处理confirm key if ((mViewFlags & ENABLED_MASK) == DISABLED) { return true; // 同样的逻辑，如果是DISABLED view，直接返回true表示处理过了 } if ((mViewFlags & CLICKABLE) == CLICKABLE && isPressed()) { setPressed(false); // 重置pressed状态 if (!mHasPerformedLongPress) { // 长按没发生的话， // This is a tap, so remove the longpress check removeLongPressCallback(); // 当up事件发生的时候，移除这些已经没用的callback return performClick(); // 调用单击onClick监听器 } } } return false; // 其他所有的Key默认不处理 } /** * Sets the pressed state for this view. * * @see #isClickable() * @see #setClickable(boolean) * * @param pressed Pass true to set the View's internal state to "pressed", or false to reverts * the View's internal state from a previously set "pressed" state. */ public void setPressed(boolean pressed) { final boolean needsRefresh = pressed != ((mPrivateFlags & PFLAG_PRESSED) == PFLAG_PRESSED); if (pressed) { mPrivateFlags |= PFLAG_PRESSED; } else { mPrivateFlags &= ~PFLAG_PRESSED; } if (needsRefresh) { refreshDrawableState(); // 这行代码会刷新View的显示状态 } dispatchSetPressed(pressed); } private void checkForLongClick(int delayOffset) { if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) { // 必须得是LONG_CLICKABLE的View mHasPerformedLongPress = false; // 设置初始值 if (mPendingCheckForLongPress == null) { // 只非空的时候才new一个 mPendingCheckForLongPress = new CheckForLongPress(); } mPendingCheckForLongPress.rememberWindowAttachCount(); postDelayed(mPendingCheckForLongPress, // post一个Runnable，注意延迟是个差值，而不是delayOffset ViewConfiguration.getLongPressTimeout() - delayOffset); } } class CheckForLongPress implements Runnable { private int mOriginalWindowAttachCount; public void run() { if (isPressed() && (mParent != null) // 当时间到了，此Runnable没被移除掉的话，并且这些条件都满足的时候， && mOriginalWindowAttachCount == mWindowAttachCount) { if (performLongClick()) { // 客户端定义的onLongClickListener监听器被触发 mHasPerformedLongPress = true; // 只有当被上面的方法处理掉了，才表示LongPress发生过了 } } } public void rememberWindowAttachCount() { mOriginalWindowAttachCount = mWindowAttachCount; } } /** * Call this view's OnLongClickListener, if it is defined. Invokes the context menu if the * OnLongClickListener did not consume the event. * * @return True if one of the above receivers consumed the event, false otherwise. */ public boolean performLongClick() { sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_LONG_CLICKED); boolean handled = false; ListenerInfo li = mListenerInfo; if (li != null && li.mOnLongClickListener != null) { // 优先触发监听器 handled = li.mOnLongClickListener.onLongClick(View.this); } if (!handled) { // 如果还没处理，显示ContextMenu如果定义了的话 handled = showContextMenu(); } if (handled) { performHapticFeedback(HapticFeedbackConstants.LONG_PRESS); } return handled; // 返回处理结果 }
接下来，看看Activity对应的onKeyDown，onKeyUp方法：
/** * Called when a key was pressed down and not handled by any of the views * inside of the activity. So, for example, key presses while the cursor * is inside a TextView will not trigger the event (unless it is a navigation * to another object) because TextView handles its own key presses. * * <p>If the focused view didn't want this event, this method is called. * * <p>The default implementation takes care of {@link KeyEvent#KEYCODE_BACK} * by calling {@link #onBackPressed()}, though the behavior varies based * on the application compatibility mode: for * {@link android.os.Build.VERSION_CODES#ECLAIR} or later applications, * it will set up the dispatch to call {@link #onKeyUp} where the action * will be performed; for earlier applications, it will perform the * action immediately in on-down, as those versions of the platform * behaved. * * <p>Other additional default key handling may be performed * if configured with {@link #setDefaultKeyMode}. * * @return Return <code>true</code> to prevent this event from being propagated * further, or <code>false</code> to indicate that you have not handled * this event and it should continue to be propagated. * @see #onKeyUp * @see android.view.KeyEvent */ public boolean onKeyDown(int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_BACK) { if (getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.ECLAIR) { // >= Android 2.0之后 event.startTracking(); // 标记追踪这个key event } else { onBackPressed(); // 2.0之前直接调用onBackPressed } return true; // 返回true表示被activity处理掉了 } if (mDefaultKeyMode == DEFAULT_KEYS_DISABLE) { return false; } else if (mDefaultKeyMode == DEFAULT_KEYS_SHORTCUT) { if (getWindow().performPanelShortcut(Window.FEATURE_OPTIONS_PANEL, keyCode, event, Menu.FLAG_ALWAYS_PERFORM_CLOSE)) { return true; } return false; } else { // Common code for DEFAULT_KEYS_DIALER & DEFAULT_KEYS_SEARCH_* boolean clearSpannable = false; boolean handled; if ((event.getRepeatCount() != 0) || event.isSystem()) { clearSpannable = true; handled = false; } else { handled = TextKeyListener.getInstance().onKeyDown( null, mDefaultKeySsb, keyCode, event); if (handled && mDefaultKeySsb.length() > 0) { // something useable has been typed - dispatch it now. final String str = mDefaultKeySsb.toString(); clearSpannable = true; switch (mDefaultKeyMode) { case DEFAULT_KEYS_DIALER: Intent intent = new Intent(Intent.ACTION_DIAL, Uri.parse("tel:" + str)); intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); startActivity(intent); break; case DEFAULT_KEYS_SEARCH_LOCAL: startSearch(str, false, null, false); break; case DEFAULT_KEYS_SEARCH_GLOBAL: startSearch(str, false, null, true); break; } } } if (clearSpannable) { mDefaultKeySsb.clear(); mDefaultKeySsb.clearSpans(); Selection.setSelection(mDefaultKeySsb,0); } return handled; } } /** * Called when a key was released and not handled by any of the views * inside of the activity. So, for example, key presses while the cursor * is inside a TextView will not trigger the event (unless it is a navigation * to another object) because TextView handles its own key presses. * * <p>The default implementation handles KEYCODE_BACK to stop the activity * and go back. * * @return Return <code>true</code> to prevent this event from being propagated * further, or <code>false</code> to indicate that you have not handled * this event and it should continue to be propagated. * @see #onKeyDown * @see KeyEvent */ public boolean onKeyUp(int keyCode, KeyEvent event) { if (getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.ECLAIR) { // 同onKeyDown，2.0之后的版本 if (keyCode == KeyEvent.KEYCODE_BACK && event.isTracking() && !event.isCanceled()) { // 是back key，且正在追踪&event没被取消掉（从前面的分析我们知道当发生生理长按时会被标记为Canceled） onBackPressed(); // 在这种情况下执行onBackPressed表示处理掉了 return true; } } return false; }
最后是3.步骤，回到一开始DecorView.dispatchKeyEvent的最后几行代码，我们来看看PhoneWindow对应的onKeyDown，onKeyUp方法：
/** * A key was pressed down and not handled by anything else in the window. * * @see #onKeyUp * @see android.view.KeyEvent */ protected boolean onKeyDown(int featureId, int keyCode, KeyEvent event) { /* **************************************************************************** * HOW TO DECIDE WHERE YOUR KEY HANDLING GOES. * * If your key handling must happen before the app gets a crack at the event, * it goes in PhoneWindowManager. * * If your key handling should happen in all windows, and does not depend on * the state of the current application, other than that the current * application can override the behavior by handling the event itself, it * should go in PhoneFallbackEventHandler. * * Only if your handling depends on the window, and the fact that it has * a DecorView, should it go here. * ****************************************************************************/ final KeyEvent.DispatcherState dispatcher = mDecor != null ? mDecor.getKeyDispatcherState() : null; //Log.i(TAG, "Key down: repeat=" + event.getRepeatCount() // + " flags=0x" + Integer.toHexString(event.getFlags())); switch (keyCode) { case KeyEvent.KEYCODE_VOLUME_UP: // key event处理中的最后一步， case KeyEvent.KEYCODE_VOLUME_DOWN: case KeyEvent.KEYCODE_VOLUME_MUTE: { // 处理音量调节键 // Similar code is in PhoneFallbackEventHandler in case the window // doesn't have one of these. In this case, we execute it here and // eat the event instead, because we have mVolumeControlStreamType // and they don't. getAudioManager().handleKeyDown(event, mVolumeControlStreamType); return true; } case KeyEvent.KEYCODE_MENU: { onKeyDownPanel((featureId < 0) ? FEATURE_OPTIONS_PANEL : featureId, event); return true; } case KeyEvent.KEYCODE_BACK: { if (event.getRepeatCount() > 0) break; if (featureId < 0) break; // Currently don't do anything with long press. if (dispatcher != null) { dispatcher.startTracking(event, this); } return true; } } return false; } /** * A key was released and not handled by anything else in the window. * * @see #onKeyDown * @see android.view.KeyEvent */ protected boolean onKeyUp(int featureId, int keyCode, KeyEvent event) { final KeyEvent.DispatcherState dispatcher = mDecor != null ? mDecor.getKeyDispatcherState() : null; if (dispatcher != null) { dispatcher.handleUpEvent(event); } //Log.i(TAG, "Key up: repeat=" + event.getRepeatCount() // + " flags=0x" + Integer.toHexString(event.getFlags())); switch (keyCode) { case KeyEvent.KEYCODE_VOLUME_UP: case KeyEvent.KEYCODE_VOLUME_DOWN: case KeyEvent.KEYCODE_VOLUME_MUTE: { // Similar code is in PhoneFallbackEventHandler in case the window // doesn't have one of these. In this case, we execute it here and // eat the event instead, because we have mVolumeControlStreamType // and they don't. getAudioManager().handleKeyUp(event, mVolumeControlStreamType); return true; } case KeyEvent.KEYCODE_MENU: { onKeyUpPanel(featureId < 0 ? FEATURE_OPTIONS_PANEL : featureId, event); return true; } case KeyEvent.KEYCODE_BACK: { if (featureId < 0) break; if (event.isTracking() && !event.isCanceled()) { if (featureId == FEATURE_OPTIONS_PANEL) { PanelFeatureState st = getPanelState(featureId, false); if (st != null && st.isInExpandedMode) { // If the user is in an expanded menu and hits back, it // should go back to the icon menu reopenMenu(true); return true; } } closePanel(featureId); return true; } break; } case KeyEvent.KEYCODE_SEARCH: { /* * Do this in onKeyUp since the Search key is also used for * chording quick launch shortcuts. */ if (getKeyguardManager().inKeyguardRestrictedInputMode()) { break; } if (event.isTracking() && !event.isCanceled()) { launchDefaultSearch(); } return true; } } return false; }
至此所有按键事件的处理就分析完毕了，鉴于篇幅略长，我们最后稍微总结下。主要有这么几点：
1. View的各种KeyEvent.Callback接口早于Activity的对应接口被调用；
2. 整个处理环节中只要有一处表明处理掉了，则处理结束，不在往下传递；
3. 各种Callback接口的处理优先级低于监听器，也就是说各种onXXXListener的方法优先被调用。