Android4.4 SystemUI分析之PowerUI

以下分析是基于MTK Android4.4原生的SystemUI与Google 的SystemUI有微小的区别，但两者的整体框架是差不多的。

这一篇是分析SystemUI的第一篇，先从最简单的PowerUI着手，源码路径：/frameworks/base/packages/SystemUI  程序目录结构如下：

我导入Eclipse编辑，报错的原因是因为找不到Framework上的一些包和资源，这个没有关系；修改完后在使用mmm模块编译，再push到手机（eng版本）上进行调试，push后需要重启才能生效。

在AndroidManifest.xml上没有Activity注册

<intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>

所以整个程序启动是从外部启动SystemUIService的。那么是如何启动SystemUIService的呢？看下这个文件：/frameworks/base/services/java/com/android/server/SystemServer.java在这个文件中可以找到

    static final void startSystemUi(Context context) {
        Intent intent = new Intent();
        intent.setComponent(new ComponentName("com.android.systemui",
                    "com.android.systemui.SystemUIService"));
        //Slog.d(TAG, "Starting service: " + intent);
        context.startServiceAsUser(intent, UserHandle.OWNER);
    }

所以SystemUI在SystemService启动时就被调用了。

SystemUIService的关键代码如下：

package com.android.systemui;

import android.app.Service;
import android.content.Intent;
import android.content.res.Configuration;
import android.os.IBinder;
import android.util.Log;

import java.io.FileDescriptor;
import java.io.PrintWriter;
import java.util.HashMap;

public class SystemUIService extends Service {
    private static final String TAG = "SystemUIService";

    /**
     * The classes of the stuff to start.
     */
    private final Class<?>[] SERVICES = new Class[] {
            com.android.systemui.recent.Recents.class,
            com.android.systemui.statusbar.SystemBars.class,
            com.android.systemui.usb.StorageNotification.class,
            com.android.systemui.power.PowerUI.class,
            com.android.systemui.media.RingtonePlayer.class,
            com.android.systemui.settings.SettingsUI.class,
        };

    /**
     * Hold a reference on the stuff we start.
     */
    private final SystemUI[] mServices = new SystemUI[SERVICES.length];

    @Override
    public void onCreate() {
        HashMap<Class<?>, Object> components = new HashMap<Class<?>, Object>();
        final int N = SERVICES.length;
        for (int i=0; i<N; i++) {
            Class<?> cl = SERVICES[i];
            Log.d(TAG, "loading: " + cl);
            Log.d("dzt", "loading: " + cl);
            try {
                mServices[i] = (SystemUI)cl.newInstance();
            } catch (IllegalAccessException ex) {
                throw new RuntimeException(ex);
            } catch (InstantiationException ex) {
                throw new RuntimeException(ex);
            }
            mServices[i].mContext = this;
            mServices[i].mComponents = components;
            Log.d(TAG, "running: " + mServices[i]);
            Log.d("dzt", "running: " + mServices[i]);
            mServices[i].start();
        }
    }
}

这些类

com.android.systemui.recent.Recents.class,
            com.android.systemui.statusbar.SystemBars.class,
            com.android.systemui.usb.StorageNotification.class,
            com.android.systemui.power.PowerUI.class,
            com.android.systemui.media.RingtonePlayer.class,
            com.android.systemui.settings.SettingsUI.class,

都是继承于：SystemUI，在SystemUIService的OnCreate()函数中会创建实例，并调用mServices[i].start();方法。

下面就分析最简单的com.android.systemui.power.PowerUI.class

在PowerUI的start()方法中，注册一些监听器

public void start() {

        mLowBatteryAlertCloseLevel = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_lowBatteryCloseWarningLevel);
        mLowBatteryReminderLevels[0] = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_lowBatteryWarningLevel);
        mLowBatteryReminderLevels[1] = mContext.getResources().getInteger(
                com.android.internal.R.integer.config_criticalBatteryWarningLevel);

        final PowerManager pm = (PowerManager) mContext.getSystemService(Context.POWER_SERVICE);
        mScreenOffTime = pm.isScreenOn() ? -1 : SystemClock.elapsedRealtime();

        // Register for Intent broadcasts for...
        IntentFilter filter = new IntentFilter();
        filter.addAction(Intent.ACTION_BATTERY_CHANGED);
        filter.addAction(Intent.ACTION_SCREEN_OFF);
        filter.addAction(Intent.ACTION_SCREEN_ON);
        /// M: Support show battery level when configuration changed. @{
        filter.addAction(Intent.ACTION_CONFIGURATION_CHANGED);
        /// M: Support show battery level when configuration changed. @}
        /// M: Hide low battery dialog when PowerOffAlarm ring. @{
        filter.addAction("android.intent.action.normal.boot");
        filter.addAction("android.intent.action.ACTION_SHUTDOWN_IPO");
        /// M: Hide low battery dialog when PowerOffAlarm ring. @}
        mContext.registerReceiver(mIntentReceiver, filter, null, mHandler);
    }

例如监听ACTION_BATTERY_CHANGED判断电量的大小，如果低电给一个提示给用户，其它的ACTION也都是根据广播来处理一些特定的事情，如果跟电源相关功能需要定制或添加新的监听器都可以在这个类中修改。