Android的全局键（home键/长按耳机键）详解【android源码解析八】

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如果想在Android手机要想扩展一个实体键，就我知道而言有两种方法，基于Android4.0的源码来分析的和2.3的源码有点区别，区别不大，下面分享给大家：

转载请标明出处：

（一）可以在frameworks层的KeyEvent.java这个类中定义一个值，在PhoneWindowManager.java这个类中做处理就可以了。（Home键就是这么实现的）。效果图如下：

（二）可以利用广播的形式，frameworks层PhoneWindow.java这个类的onKeyDown( )对这个实体键发广播，上层接受这个广播来处理也可以达到这个效果。耳机键就是利用广播来接受的。无论在哪个界面长按耳机键，都会进入到音乐的界面。（长按耳机键的）效果图如下：

下面我详细展开来说明一下：

一、先说Home键的实现的大致流程，即---->为什么点击Home键，都进入到launcher的待机界面；

（1）Home键的定义在

step1: frameworks/base/core/java/android/view/KeyEvent.java这个类中,在KeyEvent.java这个类中有个static的静态块：

  static {
        populateKeycodeSymbolicNames();
    }

step2: 这个populateKeycodeSymbolicNames（）方法其实就是加载了许多键的定义，把这些键对应的值都放到Array数组中。

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键对应的值如下：

 /** 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键的处理如下：在
step1: frameworks/base/policy/src/com/android/internal/policy/impl/PhoneWindowManager.java这个类中：

在这个方法interceptKeyBeforeDispatching（... ... ...）中处理有对Home，Search，menu，音量大小键等等：

  /** {@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《网上有例子说怎么在自己的应用中屏蔽Home键》--->原理：是在你的应用的Activity中加入了锁屏的type，因为系统对锁屏界面，点击Home键失效！网摘代码如下：

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，对锁屏模式的处理：

            // 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: 我们来看点击home键，为什么进入到launcher的待机界面：

            // 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: 系统会判断，当前点击Home键并且没有电话打入的情况，才对Home键进行处理---->launchHomeFromHotKey();进入到----->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: 也是对锁屏模式有个判断，如果不在锁屏模式，就launch Home---->startDockOrHome(),进入——>

   void startDockOrHome() {
        Intent dock = createHomeDockIntent();
        if (dock != null) {
            try {
                mContext.startActivity(dock);
                return;
            } catch (ActivityNotFoundException e) {
            }
        }
        mContext.startActivity(mHomeIntent);
    }

Step 7: 其实这个createHomeDockIntent（）方法就是对android手机的几种模式进行判断，

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，车载模式或者桌面模式，就返回dock不为空，否则为空。启动这个mHomeIntent。----->mHomeIntent定义如下：

           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: 这个mHomeIntent就是启动activity中配置Category属性的值为CATEGORY_HOME，启动的时候新启动一个任务，不是在当前的这个任务中启动launcherHome，而是新建一个task。

FLAG_ACTIVITY_RESET_TASK_IF_NEEDED标记进入前台时（典型的操作是用户在主画面重启它），这个Activity和它之上的都将关闭，以至于用户不能再返回到它们，但是可以回到之前的Activity。

到这为止，Home键的流程已经分析完了。

二、下面看看长按耳机键接受的广播的处理方式：

（1）这个长按耳机键捕获是在PhoneWindow.java类的onKeyDown()中，然后发送有序的广播---->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;
            }

接受这个长按耳机键的广播是在Music的app中的----->

publicclassMediaButtonIntentReceiverextendsBroadcastReceiver{......}

，需要在Manifest.xml中注册这个广播<intent-filter>

</intent-filter>。---->注册MediaButtonReceiver这个广播，

这个类中onReceive（）方法定义的：代码如下--->

    @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) { ... ... }做的处理，event.getRepeatCount() == 0这个判断的意思是“是否长按耳机键？”，如果长按耳机键event.getRepeatCount() 的值就一直增加。

step 2:短按耳机键：播放/暂停 --->音乐；短按启动MediaPlaybackService.java这个类，并且传入参数---->在这个服务类中有个接受广播的内部类：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);
            }
        }
    };

通过：如下方法来控制点击播放音乐，再次点击暂停，如此循环。

else if (CMDTOGGLEPAUSE.equals(cmd) || TOGGLEPAUSE_ACTION.equals(action)) {

if (isPlaying()) {

pause();

mInternalPause = false;

} else {

play();

}

内部类的广播是在启动MediaPlaybackService.java中注册的，解除注册在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: 长按耳机键--->发消息给mHandler,

       mHandler.removeMessages(MSG_LONGPRESS_TIMEOUT);

在MediaButtonIntentReceiver.java中有个内部类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;
            }
        }
    };

长按耳机后就启动MusicBrowserActivity.java这个音乐播放类。并且传入参数“autoshuffle==true”，这个启动和launcher的启动相似，也是启动一个新的任务task，但是这个后面的标志有不同的地方Intent.FLAG_ACTIVITY_CLEAR_TOP。

到这为止就是实现了在任何界面长按耳机键都能进入到music的主界面。

总结如下：

其实启动的时候，要注意当前activity的launcherMode是什么，如果是SingleTask，就要小心一下。比如说：想要长按耳机键，进入到launcher的Mainmenu界面，这时候如果单纯的用以上方法套，返回键点击的时候不会回到上个activity中，会有问题。因为launcher是一直启动的运行于每个task之中的，你再次启动Launcher的时候，无论是否设置属性“i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK)”，都会把前一个activity给finish掉，launcher会在栈顶也是栈底。因为launcher的launcherMode=singleTask。我们可以做个实验；

三、例子写两个app，一个属性为singletask，一个为standard。应singletask的启动standard的activity，然后在再次基础上启动singletask的activity，看standard的activity是否会destory掉。

step1：先看截图：

launchMode="singleTask"launchMode="standard"

Step 2：先启动launchMode="singleTask"的activity---->点击调用第二个App2的launchMode="standard"---->

点击按钮调用第一个App1的launchMode="singleTask"---->点击返回键。看log分析：

（1）点击启动launchMode="singleTask"的activity的log如下：

（2）点击调用第二个App2的launchMode="standard"的activity的log如下图：

（3）点击调用第一个App1launchMode="singleTask"的activity的log如下：
分析如下：看到这时候App2Activity--22已经执行了onStop()和onDestroy（）方法了。验证了我以上的说法。

（4）点击返回键---->直接回到了launcher界面。log如下：

备注：要想解决以上问题也是可以的。就是在以上第（2）步：点击调用第二个App2的launchMode="standard"的activity的时候设置flag。Intent.FLAG_ACTIVITY_NEW_TASK。就可以解决以上问题了，每次启动一个新的任务，这样就能返回到App2Activity了。

（1）点击启动launchMode="singleTask"的activity的log如下：