如果想在Android手機要想擴展一個實體鍵，就我知道而言有兩種方法，基於Android4.0的源碼來分析的和2.3的源碼有點區別，區別不大，下面分享給大家：
轉載請標明出處：
（一）可以在frameworks層的KeyEvent.java這個類中定義一個值，在PhoneWindowManager.java這個類中做處理就可以了。（Home鍵就是這麼實現的）。效果圖如下：
（二）可以利用廣播的形式，frameworks層PhoneWindow.java這個類的onKeyDown( )對這個實體鍵發廣播，上層接受這個廣播來處理也可以達到這個效果。耳機鍵就是利用廣播來接受的。無論在哪個界面長按耳機鍵，都會進入到音樂的界面。（長按耳機鍵的）效果圖如下：
下面我詳細展開來說明一下：
一、先說Home鍵的實現的大致流程，即---->爲什麼點擊Home鍵，都進入到launcher的待機界面；
（1）Home鍵的定義在
step1: frameworks/base/core/java/android/view/KeyEvent.java這個類中,在KeyEvent.java這個類中有個static的靜態塊：
static {
populateKeycodeSymbolicNames();
}
step2: 這個populateKeycodeSymbolicNames（）方法其實就是加載了許多鍵的定義，把這些鍵對應的值都放到Array數組中。
private static void populateKeycodeSymbolicNames() {
SparseArray<String> names = KEYCODE_SYMBOLIC_NAMES;
names.append(KEYCODE_UNKNOWN, "KEYCODE_UNKNOWN");
names.append(KEYCODE_SOFT_LEFT, "KEYCODE_SOFT_LEFT");
names.append(KEYCODE_SOFT_RIGHT, "KEYCODE_SOFT_RIGHT");
names.append(KEYCODE_HOME, "KEYCODE_HOME");
names.append(KEYCODE_BACK, "KEYCODE_BACK");
names.append(KEYCODE_CALL, "KEYCODE_CALL");
names.append(KEYCODE_ENDCALL, "KEYCODE_ENDCALL");
names.append(KEYCODE_0, "KEYCODE_0");
names.append(KEYCODE_1, "KEYCODE_1");
names.append(KEYCODE_2, "KEYCODE_2");
names.append(KEYCODE_3, "KEYCODE_3");
names.append(KEYCODE_4, "KEYCODE_4");
names.append(KEYCODE_5, "KEYCODE_5");
names.append(KEYCODE_6, "KEYCODE_6");
names.append(KEYCODE_7, "KEYCODE_7");
names.append(KEYCODE_8, "KEYCODE_8");
names.append(KEYCODE_9, "KEYCODE_9");
step3: 而Home鍵對應的值如下：
/** Key code constant: Home key.
* This key is handled by the framework and is never delivered to applications. */
public static final int KEYCODE_HOME = 3;
（2）Home鍵的處理如下：在
step1: frameworks/base/policy/src/com/android/internal/policy/impl/PhoneWindowManager.java這個類中：
在這個方法interceptKeyBeforeDispatching（... ... ...）中處理有對Home，Search，menu，音量大小鍵等等：
/** {@inheritDoc} */
@Override
public long interceptKeyBeforeDispatching(WindowState win, KeyEvent event, int policyFlags) {
final boolean keyguardOn = keyguardOn();
final int keyCode = event.getKeyCode();
final int repeatCount = event.getRepeatCount();
final int metaState = event.getMetaState();
final int flags = event.getFlags();
final boolean down = event.getAction() == KeyEvent.ACTION_DOWN;
final boolean canceled = event.isCanceled();
if (false) {
Log.d(TAG, "interceptKeyTi keyCode=" + keyCode + " down=" + down + " repeatCount="
+ repeatCount + " keyguardOn=" + keyguardOn + " mHomePressed=" + mHomePressed);
}
// If we think we might have a volume down & power key chord on the way
// but we're not sure, then tell the dispatcher to wait a little while and
// try again later before dispatching.
if ((flags & KeyEvent.FLAG_FALLBACK) == 0) {
if (mVolumeDownKeyTriggered && !mPowerKeyTriggered) {
final long now = SystemClock.uptimeMillis();
final long timeoutTime = mVolumeDownKeyTime + SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS;
if (now < timeoutTime) {
return timeoutTime - now;
}
}
if (keyCode == KeyEvent.KEYCODE_VOLUME_DOWN
&& mVolumeDownKeyConsumedByScreenshotChord) {
if (!down) {
mVolumeDownKeyConsumedByScreenshotChord = false;
}
return -1;
}
}
// First we always handle the home key here, so applications
// can never break it, although if keyguard is on, we do let
// it handle it, because that gives us the correct 5 second
// timeout.
if (keyCode == KeyEvent.KEYCODE_HOME) {
// If we have released the home key, and didn't do anything else
// while it was pressed, then it is time to go home!
if (mHomePressed && !down) {
mHomePressed = false;
if (!canceled) {
// If an incoming call is ringing, HOME is totally disabled.
// (The user is already on the InCallScreen at this point,
// and his ONLY options are to answer or reject the call.)
boolean incomingRinging = false;
try {
ITelephony telephonyService = getTelephonyService();
if (telephonyService != null) {
incomingRinging = telephonyService.isRinging();
}
} catch (RemoteException ex) {
Log.w(TAG, "RemoteException from getPhoneInterface()", ex);
}
if (incomingRinging) {
Log.i(TAG, "Ignoring HOME; there's a ringing incoming call.");
} else {
launchHomeFromHotKey();
}
} else {
Log.i(TAG, "Ignoring HOME; event canceled.");
}
return -1;
}
// If a system window has focus, then it doesn't make sense
// right now to interact with applications.
WindowManager.LayoutParams attrs = win != null ? win.getAttrs() : null;
if (attrs != null) {
final int type = attrs.type;
if (type == WindowManager.LayoutParams.TYPE_KEYGUARD
|| type == WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG) {
// the "app" is keyguard, so give it the key
return 0;
}
final int typeCount = WINDOW_TYPES_WHERE_HOME_DOESNT_WORK.length;
for (int i=0; i<typeCount; i++) {
if (type == WINDOW_TYPES_WHERE_HOME_DOESNT_WORK[i]) {
// don't do anything, but also don't pass it to the app
return -1;
}
}
}
if (down) {
if (repeatCount == 0) {
mHomePressed = true;
} else if ((event.getFlags() & KeyEvent.FLAG_LONG_PRESS) != 0) {
if (!keyguardOn) {
handleLongPressOnHome();
}
}
}
return -1;
} else if (keyCode == KeyEvent.KEYCODE_MENU) {
........
Step2: 插曲《網上有例子說怎麼在自己的應用中屏蔽Home鍵》--->原理：是在你的應用的Activity中加入了鎖屏的type，因爲系統對鎖屏界面，點擊Home鍵失效！網摘代碼如下：public class DMActivity extends Activity {
private boolean flag = true;//true位屏蔽，false位不屏蔽
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
@Override
public void onAttachedToWindow() {
if(flag) {
this.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD);
}
super.onAttachedToWindow();
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if(keyCode == KeyEvent.KEYCODE_HOME){
return true;
}
return super.onKeyDown(keyCode, event);
}
}
Step3: 真正的原因如下，對鎖屏模式的處理：
// If a system window has focus, then it doesn't make sense
// right now to interact with applications.
WindowManager.LayoutParams attrs = win != null ? win.getAttrs() : null;
if (attrs != null) {
final int type = attrs.type;
if (type == WindowManager.LayoutParams.TYPE_KEYGUARD
|| type == WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG) {
// the "app" is keyguard, so give it the key
return 0;
}
final int typeCount = WINDOW_TYPES_WHERE_HOME_DOESNT_WORK.length;
for (int i=0; i<typeCount; i++) {
if (type == WINDOW_TYPES_WHERE_HOME_DOESNT_WORK[i]) {
// don't do anything, but also don't pass it to the app
return -1;
}
}
}
Step4: 我們來看點擊home鍵，爲什麼進入到launcher的待機界面：
// If we have released the home key, and didn't do anything else
// while it was pressed, then it is time to go home!
if (mHomePressed && !down) {
mHomePressed = false;
if (!canceled) {
// If an incoming call is ringing, HOME is totally disabled.
// (The user is already on the InCallScreen at this point,
// and his ONLY options are to answer or reject the call.)
boolean incomingRinging = false;
try {
ITelephony telephonyService = getTelephonyService();
if (telephonyService != null) {
incomingRinging = telephonyService.isRinging();
}
} catch (RemoteException ex) {
Log.w(TAG, "RemoteException from getPhoneInterface()", ex);
}
if (incomingRinging) {
Log.i(TAG, "Ignoring HOME; there's a ringing incoming call.");
} else {
launchHomeFromHotKey();
}
} else {
Log.i(TAG, "Ignoring HOME; event canceled.");
}
return -1;
}
Step5: 系統會判斷，當前點擊Home鍵並且沒有電話打入的情況，纔對Home鍵進行處理---->launchHomeFromHotKey();進入到----->launchHomeFromHotKey()方法中：
/**
* A home key -> launch home action was detected. Take the appropriate action
* given the situation with the keyguard.
*/
void launchHomeFromHotKey() {
if (mKeyguardMediator.isShowingAndNotHidden()) {
// don't launch home if keyguard showing
} else if (!mHideLockScreen && mKeyguardMediator.isInputRestricted()) {
// when in keyguard restricted mode, must first verify unlock
// before launching home
mKeyguardMediator.verifyUnlock(new OnKeyguardExitResult() {
public void onKeyguardExitResult(boolean success) {
if (success) {
try {
ActivityManagerNative.getDefault().stopAppSwitches();
} catch (RemoteException e) {
}
sendCloseSystemWindows(SYSTEM_DIALOG_REASON_HOME_KEY);
startDockOrHome();
}
}
});
} else {
// no keyguard stuff to worry about, just launch home!
try {
ActivityManagerNative.getDefault().stopAppSwitches();
} catch (RemoteException e) {
}
sendCloseSystemWindows(SYSTEM_DIALOG_REASON_HOME_KEY);
startDockOrHome();
}
}
Step6: 也是對鎖屏模式有個判斷，如果不在鎖屏模式，就launch Home---->startDockOrHome(),進入——>
void startDockOrHome() {
Intent dock = createHomeDockIntent();
if (dock != null) {
try {
mContext.startActivity(dock);
return;
} catch (ActivityNotFoundException e) {
}
}
mContext.startActivity(mHomeIntent);
}
Step 7: 其實這個createHomeDockIntent（）方法就是對android手機的幾種模式進行判斷，
The device is not in either car mode or desk mode
The device is in car mode but ENABLE_CAR_DOCK_HOME_CAPTURE is false
The device is in desk mode but ENABLE_DESK_DOCK_HOME_CAPTURE is false
The device is in car mode but there's no CAR_DOCK app with METADATA_DOCK_HOME
The device is in desk mode but there's no DESK_DOCK app with METADATA_DOCK_HOME
如果是以上模式，車載模式或者桌面模式，就返回dock不爲空，否則爲空。啓動這個mHomeIntent。----->mHomeIntent定義如下：
mHomeIntent = new Intent(Intent.ACTION_MAIN, null);
mHomeIntent.addCategory(Intent.CATEGORY_HOME);
mHomeIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK
| Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED);Step 8: 這個mHomeIntent就是啓動activity中配置Category屬性的值爲CATEGORY_HOME，啓動的時候新啓動一個任務，不是在當前的這個任務中啓動launcherHome，而是新建一個task。
FLAG_ACTIVITY_RESET_TASK_IF_NEEDED標記進入前臺時（典型的操作是用戶在主畫面重啓它），這個Activity和它之上的都將關閉，以至於用戶不能再返回到它們，但是可以回到之前的Activity。
到這爲止，Home鍵的流程已經分析完了。
二 、下面看看長按耳機鍵接受的廣播的處理方式：
（1）這個長按耳機鍵捕獲是在PhoneWindow.java類的onKeyDown()中，然後發送有序的廣播---->如下：
case KeyEvent.KEYCODE_HEADSETHOOK:
case KeyEvent.KEYCODE_MEDIA_STOP:
case KeyEvent.KEYCODE_MEDIA_NEXT:
case KeyEvent.KEYCODE_MEDIA_PREVIOUS:
case KeyEvent.KEYCODE_MEDIA_REWIND:
case KeyEvent.KEYCODE_MEDIA_FAST_FORWARD: {
Intent intent = new Intent(Intent.ACTION_MEDIA_BUTTON, null);
intent.putExtra(Intent.EXTRA_KEY_EVENT, event);
getContext().sendOrderedBroadcast(intent, null);
return true;
}接受這個長按耳機鍵的廣播是在Music的app中的----->
public class MediaButtonIntentReceiver extends BroadcastReceiver{ ... ... }
， 需要在Manifest.xml中註冊這個廣播<intent-filter>
<action android:name="android.intent.action.MEDIA_BUTTON" />
</intent-filter>。---->註冊MediaButtonReceiver這個廣播，
這個類中onReceive（）方法定義的：代碼如下--->
@Override
public void onReceive(Context context, Intent intent) {
String intentAction = intent.getAction();
if (AudioManager.ACTION_AUDIO_BECOMING_NOISY.equals(intentAction)) {
Intent i = new Intent(MediaPlaybackService.SERVICECMD);
i.putExtra(MediaPlaybackService.CMDNAME, MediaPlaybackService.CMDPAUSE);
context.sendBroadcast(i);
} else if (Intent.ACTION_MEDIA_BUTTON.equals(intentAction)) {
KeyEvent event = (KeyEvent)
intent.getParcelableExtra(Intent.EXTRA_KEY_EVENT);
if (event == null) {
return;
}
int keycode = event.getKeyCode();
int action = event.getAction();
long eventtime = event.getEventTime();
// single quick press: pause/resume.
// double press: next track
// long press: start auto-shuffle mode.
String command = null;
switch (keycode) {
case KeyEvent.KEYCODE_MEDIA_STOP:
command = MediaPlaybackService.CMDSTOP;
break;
case KeyEvent.KEYCODE_HEADSETHOOK:
case KeyEvent.KEYCODE_MEDIA_PLAY_PAUSE:
command = MediaPlaybackService.CMDTOGGLEPAUSE;
break;
case KeyEvent.KEYCODE_MEDIA_NEXT:
command = MediaPlaybackService.CMDNEXT;
break;
case KeyEvent.KEYCODE_MEDIA_PREVIOUS:
command = MediaPlaybackService.CMDPREVIOUS;
break;
case KeyEvent.KEYCODE_MEDIA_PAUSE:
command = MediaPlaybackService.CMDPAUSE;
break;
case KeyEvent.KEYCODE_MEDIA_PLAY:
command = MediaPlaybackService.CMDPLAY;
break;
}
if (command != null) {
if (action == KeyEvent.ACTION_DOWN) {
if (mDown) {
if ((MediaPlaybackService.CMDTOGGLEPAUSE.equals(command) ||
MediaPlaybackService.CMDPLAY.equals(command))
&& mLastClickTime != 0
&& eventtime - mLastClickTime > LONG_PRESS_DELAY) {
mHandler.sendMessage(
mHandler.obtainMessage(MSG_LONGPRESS_TIMEOUT, context));
}
} else if (event.getRepeatCount() == 0) {
// only consider the first event in a sequence, not the repeat events,
// so that we don't trigger in cases where the first event went to
// a different app (e.g. when the user ends a phone call by
// long pressing the headset button)
// The service may or may not be running, but we need to send it
// a command.
Intent i = new Intent(context, MediaPlaybackService.class);
i.setAction(MediaPlaybackService.SERVICECMD);
if (keycode == KeyEvent.KEYCODE_HEADSETHOOK &&
eventtime - mLastClickTime < 300) {
i.putExtra(MediaPlaybackService.CMDNAME, MediaPlaybackService.CMDNEXT);
context.startService(i);
mLastClickTime = 0;
} else {
i.putExtra(MediaPlaybackService.CMDNAME, command);
context.startService(i);
mLastClickTime = eventtime;
}
mLaunched = false;
mDown = true;
}
} else {
mHandler.removeMessages(MSG_LONGPRESS_TIMEOUT);
mDown = false;
}
if (isOrderedBroadcast()) {
abortBroadcast();
}
}
}
}
step1: 在方法if (action == KeyEvent.ACTION_DOWN) { ... ... }做的處理，event.getRepeatCount() == 0這個判斷的意思是“是否長按耳機鍵？”，如果長按耳機鍵event.getRepeatCount() 的值就一直增加。
step 2:短按耳機鍵：播放/暫停 --->音樂；短按啓動MediaPlaybackService.java這個類，並且傳入參數---->在這個服務類中有個接受廣播的內部類：如下-->
private BroadcastReceiver mIntentReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
String cmd = intent.getStringExtra("command");
MusicUtils.debugLog("mIntentReceiver.onReceive " + action + " / " + cmd);
if (CMDNEXT.equals(cmd) || NEXT_ACTION.equals(action)) {
next(true);
} else if (CMDPREVIOUS.equals(cmd) || PREVIOUS_ACTION.equals(action)) {
prev();
} else if (CMDTOGGLEPAUSE.equals(cmd) || TOGGLEPAUSE_ACTION.equals(action)) {
if (isPlaying()) {
pause();
mInternalPause = false;
} else {
play();
}
} else if (CMDPAUSE.equals(cmd) || PAUSE_ACTION.equals(action)) {
pause();
mInternalPause = false;
} else if (CMDPLAY.equals(cmd)) {
play();
} else if (CMDSTOP.equals(cmd)) {
pause();
mInternalPause = false;
seek(0);
} else if (MediaAppWidgetProvider.CMDAPPWIDGETUPDATE.equals(cmd)) {
// Someone asked us to refresh a set of specific widgets, probably
// because they were just added.
int[] appWidgetIds = intent.getIntArrayExtra(AppWidgetManager.EXTRA_APPWIDGET_IDS);
mAppWidgetProvider.performUpdate(MediaPlaybackService.this, appWidgetIds);
}
}
};通過：如下方法來控制點擊播放音樂，再次點擊暫停，如此循環。
else if (CMDTOGGLEPAUSE.equals(cmd) || TOGGLEPAUSE_ACTION.equals(action)) {
if (isPlaying()) {
pause();
mInternalPause = false;
} else {
play();
}
}
內部類的廣播是在啓動MediaPlaybackService.java中註冊的，解除註冊在onDestroy（）的方法中。
IntentFilter commandFilter = new IntentFilter();
commandFilter.addAction(SERVICECMD);
commandFilter.addAction(TOGGLEPAUSE_ACTION);
commandFilter.addAction(PAUSE_ACTION);
commandFilter.addAction(NEXT_ACTION);
commandFilter.addAction(PREVIOUS_ACTION);
commandFilter.addAction(PLAYSTATUS_REQUEST);
registerReceiver(mIntentReceiver, commandFilter);
Step 3: 長按耳機鍵--->發消息給mHandler,
mHandler.removeMessages(MSG_LONGPRESS_TIMEOUT);在MediaButtonIntentReceiver.java中有個內部類Handler（）如下——>
private static Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MSG_LONGPRESS_TIMEOUT:
if (!mLaunched) {
Context context = (Context)msg.obj;
Intent i = new Intent();
i.putExtra("autoshuffle", "true");
i.setClass(context, MusicBrowserActivity.class);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TOP);
context.startActivity(i);
mLaunched = true;
}
break;
}
}
};長按耳機後就啓動MusicBrowserActivity.java這個音樂播放類。並且傳入參數“autoshuffle==true”，這個啓動和launcher的啓動相似，也是啓動一個新的任務task，但是這個後面的標誌有不同的地方Intent.FLAG_ACTIVITY_CLEAR_TOP。
到這爲止就是實現了在任何界面長按耳機鍵都能進入到music的主界面。
總結如下：
其實啓動的時候，要注意當前activity的launcherMode是什麼，如果是SingleTask，就要小心一下。比如說：想要長按耳機鍵，進入到launcher的Mainmenu界面，這時候如果單純的用以上方法套，返回鍵點擊的時候不會回到上個activity中，會有問題。因爲launcher是一直啓動的運行於每個task之中的，你再次啓動Launcher的時候，無論是否設置屬性“i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK)”，都會把前一個activity給finish掉，launcher會在棧頂也是棧底。因爲launcher的launcherMode=singleTask。我們可以做個實驗；
三、例子寫兩個app，一個屬性爲singletask，一個爲standard。應singletask的啓動standard的activity，然後在再次基礎上啓動singletask的activity，看standard的activity是否會destory掉。
step1：先看截圖：
launchMode="singleTask" launchMode="standard" 
Step 2：先啓動launchMode="singleTask"的activity---->點擊調用第二個App2的launchMode="standard"---->
點擊按鈕調用第一個App1的launchMode="singleTask"---->點擊返回鍵。看log分析：
（1）點擊啓動launchMode="singleTask"的activity的log如下：
（2）點擊調用第二個App2的launchMode="standard"的activity的log如下圖： 
（3）點擊調用第一個App1launchMode="singleTask"的activity的log如下： 
分析如下：看到這時候App2Activity--22已經執行了onStop()和onDestroy（）方法了。驗證了我以上的說法。
（4）點擊返回鍵---->直接回到了launcher界面。log如下：
備註：要想解決以上問題也是可以的。就是在以上第（2）步：點擊調用第二個App2的launchMode="standard"的activity的時候設置flag。Intent.FLAG_ACTIVITY_NEW_TASK。就可以解決以上問題了，每次啓動一個新的任務，這樣就能返回到App2Activity了。
（1）點擊啓動launchMode="singleTask"的activity的log如下：
（2）點擊調用第二個App2的launchMode="standard"的activity的log如下圖：
（3）點擊調用第一個App1launchMode="singleTask"的activity的log如下：
看到如上圖:App2Activity--22--->只是onStop（）了，沒有onDestroy掉。
（4）點擊返回鍵---->直接回到了launcher界面---->log如下：
（5）通過log，我們可以看出返回到App2Activity了，我們再次點擊返回鍵，--->返回到Launcher界面的log如下：
通過以上驗證說明我的結論是正確的。launcherMode一直是android的核心技術，通過這次我會更加注意到activity的LauncherMode的。
歡迎各界人士留言，討論，拍磚！轉載請標明出處！
