Android长按Power键弹出关机Dialog框GlobalActions解析

Android长按关机键，会弹出关机的对话框，如下图：

现在分析一下详细的流程：

1)  PWM中，会调用

 private void interceptPowerKeyDown(boolean handled) {
     mPowerKeyHandled = handled;
     if (!handled) {
         mHandler.postDelayed(mPowerLongPress, ViewConfiguration.getGlobalActionKeyTimeout());
     }
 }

从而进入mPowerLongPress

 private final Runnable mPowerLongPress = new Runnable() {
     @Override
     public void run() {
         // The context isn't read
         if (mLongPressOnPowerBehavior < 0) {
             mLongPressOnPowerBehavior = mContext.getResources().getInteger(
                     com.android.internal.R.integer.config_longPressOnPowerBehavior);
         }
         ...

         switch (resolvedBehavior) {
         case LONG_PRESS_POWER_NOTHING:
             break;
         case LONG_PRESS_POWER_GLOBAL_ACTIONS:
             mPowerKeyHandled = true;
             if (!performHapticFeedbackLw(null, HapticFeedbackConstants.LONG_PRESS, false)) {
                 performAuditoryFeedbackForAccessibilityIfNeed();
             }
             sendCloseSystemWindows(SYSTEM_DIALOG_REASON_GLOBAL_ACTIONS);
             showGlobalActionsDialog();
             break;
             ...
         }
     }
 };

调用showGlobalActionsDialog

 void showGlobalActionsDialog() {
     if (mGlobalActions == null) {
         mGlobalActions = new GlobalActions(mContext, mWindowManagerFuncs);
     }
     final boolean keyguardShowing = keyguardIsShowingTq();
     mGlobalActions.showDialog(keyguardShowing, isDeviceProvisioned());
     if (keyguardShowing) {
         // since it took two seconds of long press to bring this up,
         // poke the wake lock so they have some time to see the dialog.
         mKeyguardMediator.userActivity();
     }
 }

分两步来进行，首先创建GlobalActions， 然后在showDialog出来，主要的功能实在showDialog中完成的，

 public void showDialog(boolean keyguardShowing, boolean isDeviceProvisioned) {
     mKeyguardShowing = keyguardShowing;
     mDeviceProvisioned = isDeviceProvisioned;
     if (mDialog != null) {
         mDialog.dismiss();
         mDialog = null;
         // Show delayed, so that the dismiss of the previous dialog completes
         mHandler.sendEmptyMessage(MESSAGE_SHOW);
     } else {
         handleShow();
     }
 }

然后调用handleShow

 private void handleShow() {
     awakenIfNecessary();
     mDialog = createDialog();
     prepareDialog();

     WindowManager.LayoutParams attrs = mDialog.getWindow().getAttributes();
     attrs.setTitle("GlobalActions");
     mDialog.getWindow().setAttributes(attrs);
     mDialog.show();
     mDialog.getWindow().getDecorView().setSystemUiVisibility(View.STATUS_BAR_DISABLE_EXPAND);
 }

在createDialog中主要是准备Dialog显示的数据，最关键的是mItems, 这代表关机时候显示的每一项，每一项实际是一个action，里面定义了如何创建Diaolg以及点击时的响应，

以添加飞行模式为例，

 // last: silent mode
 if (SHOW_SILENT_TOGGLE) {
     mItems.add(mSilentModeAction);
 }

Action接口的实现：

 Implemented By
   GlobalActions.SilentModeTriStateAction
   GlobalActions.SinglePressAction
   GlobalActions.ToggleAction

每一项的动作对应的View添加进MyAdapter，通过ListView来管理

 private MyAdapter mAdapter;

在创建Item的时候，

 public View getView(int position, View convertView, ViewGroup parent) {
     Action action = getItem(position);
     return action.create(mContext, convertView, parent, LayoutInflater.from(mContext));
 }

会分别调用每一个Action的onCreate来创建每一个Item View，每种Item View对应的实现了Action的接口，从而定义不同的点击动作

以来电模式的选择为例，

createItem：

 public View create(Context context, View convertView, ViewGroup parent,
         LayoutInflater inflater) {
     View v = inflater.inflate(R.layout.global_actions_silent_mode, parent, false);

     int selectedIndex = ringerModeToIndex(mAudioManager.getRingerMode());
     for (int i = 0; i < 3; i++) {
         View itemView = v.findViewById(ITEM_IDS[i]);
         itemView.setSelected(selectedIndex == i);
         // Set up click handler
         itemView.setTag(i);
         itemView.setOnClickListener(this);
     }
     return v;
 }

item 响应事件:

 public void onClick(View v) {
     if (!(v.getTag() instanceof Integer)) return;

     int index = (Integer) v.getTag();
     mAudioManager.setRingerMode(indexToRingerMode(index));
     mHandler.sendEmptyMessageDelayed(MESSAGE_DISMISS, DIALOG_DISMISS_DELAY);
 }

当点击了震动后,会调用AudioManager的setRingMode,经过AudioService处理后，会发出RINGER_MODE_CHAGNED_ACTION的广播，然后GlobalActions会接收到广播：

 private BroadcastReceiver mRingerModeReceiver = new BroadcastReceiver() {
     @Override
     public void onReceive(Context context, Intent intent) {
         if (intent.getAction().equals(AudioManager.RINGER_MODE_CHANGED_ACTION)) {
             mHandler.sendEmptyMessage(MESSAGE_REFRESH);
         }
     }
 };

 private Handler mHandler = new Handler() {
         public void handleMessage(Message msg) {
             switch (msg.what) {
             case MESSAGE_DISMISS:
                 if (mDialog != null) {
                     mDialog.dismiss();
                 }
                 break;
             case MESSAGE_REFRESH:
                 refreshSilentMode();
                 mAdapter.notifyDataSetChanged();
                 break;
             case MESSAGE_SHOW:
                 handleShow();
                 break;
             }
         }
     };

最终会在Handler中更新图片，然后响应刚才的dismiss事件mHandler.sendEmptyMessageDelayed(MESSAGE_DISMISS, DIALOG_DISMISS_DELAY);让对话框消失

Android通过这样的方式，让程序的扩展性得到了很大的提升，这是值得借鉴的地方