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