在 packages/apps/Settings/src/com/android/settings/DevelopmentSettings.java 找到关于 USB Debug Enable 的代码：
1 Settings.Secure.putInt(getContentResolver(), Settings.Secure.ADB_ENABLED, 0 );
Settings.Secure.putInt(getContentResolver(), Settings.Secure.ADB_ENABLED, 0);
别处将根据其值动态变化做出相应动作如状态栏消息提示。
void observe() {
ContentResolver resolver = mContext.getContentResolver();
resolver.registerContentObserver(Settings.Secure.getUriFor(
Settings.Secure.ADB_ENABLED), false , this );
update();
}
@Override public void onChange( boolean selfChange) {
update();
}
public void update() {
ContentResolver resolver = mContext.getContentResolver();
mAdbEnabled = Settings.Secure.getInt(resolver,
Settings.Secure.ADB_ENABLED, 0 ) != 0 ;
updateAdbNotification();
}
void observe() {
ContentResolver resolver = mContext.getContentResolver();
resolver.registerContentObserver(Settings.Secure.getUriFor(
Settings.Secure.ADB_ENABLED), false, this);
update();
}
@Override public void onChange(boolean selfChange) {
update();
}
public void update() {
ContentResolver resolver = mContext.getContentResolver();
mAdbEnabled = Settings.Secure.getInt(resolver,
Settings.Secure.ADB_ENABLED, 0) != 0;
updateAdbNotification();
}
当激活时，在状态栏中给出通知提示：
notificationManager.notify(
com.android.internal .R. string .adb_active_notification_title,
mAdbNotification);
notificationManager.notify(
com.android.internal.R.string.adb_active_notification_title,
mAdbNotification);
知的内容在资源字符串（英文）在字符串资源文件 frameworks/base/core/res/res/values/strings.xml 中， 定义如下：
<!-- Title of notification shown when ADB is actively connected to the phone. --> < string name = "adbactivenotificationtitle" > USB debugging connected </ string > <!-- Message of notification shown when ADB is actively connected to the phone. --> < string name = "adbactivenotificationmessage" > A computer is connected to your phone. </ string >
<!-- Title of notification shown when ADB is actively connected to the phone. --> <string name="adbactivenotificationtitle">USB debugging connected</string> <!-- Message of notification shown when ADB is actively connected to the phone. --> <string name="adbactivenotificationmessage">A computer is connected to your phone.</string>
改变该 Settings 值将通过如下方式影响到实际使用：
在文件中 frameworks/base/services/java/com/android/server/SystemServer.java
private class AdbSettingsObserver extends ContentObserver {
public AdbSettingsObserver() {
super ( null );
}
@Override
public void onChange( boolean selfChange) {
boolean enableAdb = (Settings.Secure.getInt(mContentResolver,
Settings.Secure.ADB_ENABLED, 0 ) > 0 );
// setting this secure property will start or stop adbd
SystemProperties.set("persist.service.adb.enable" , enableAdb ? "1" : "0" );
}
}
private class AdbSettingsObserver extends ContentObserver {
public AdbSettingsObserver() {
super(null);
}
@Override
public void onChange(boolean selfChange) {
boolean enableAdb = (Settings.Secure.getInt(mContentResolver,
Settings.Secure.ADB_ENABLED, 0) > 0);
// setting this secure property will start or stop adbd
SystemProperties.set("persist.service.adb.enable", enableAdb ? "1" : "0");
}
}
可见，当设置系统属性 persist.service.adb.enable 的值时，将影响到 adbd 守护进程相应动作 ( 停止和开启 ) ，这将影响到是否查看 log 等供开发者使用的 adb 功能。
Bug 案例分析：
private void updateAdbNotification() {
Log.d(TAG, "2. mBatteryPlugged=" +mBatteryPlugged);
if (mAdbEnabled && mBatteryPlugged == BatteryManager.BATTERYPLUGGEDUSB) {
Log.d(TAG, "adb enabled, Battery Plugged usb" );
if ( "0" .equals(SystemProperties.get( "persist.adb.notify" ))) {
Log.d(TAG, "return directly" );
return ;
}
if (!mAdbNotificationShown) {
//…省略部分代码
mAdbNotificationShown = true ;
notificationManager.notify(
com.android.internal.R.string.adb_active_notification_title,
mAdbNotification);
}
}
} else if (mAdbNotificationShown) {
//…省略部分代码
mAdbNotificationShown = false ;
notificationManager.cancel(
com.android.internal.R.string.adb_active_notification_title);
}
}
}
private void updateAdbNotification() {
Log.d(TAG, "2. mBatteryPlugged="+mBatteryPlugged);
if (mAdbEnabled && mBatteryPlugged == BatteryManager.BATTERYPLUGGEDUSB) {
Log.d(TAG, "adb enabled, Battery Plugged usb");
if ("0".equals(SystemProperties.get("persist.adb.notify"))) {
Log.d(TAG, "return directly");
return;
}
if (!mAdbNotificationShown) {
//…省略部分代码
mAdbNotificationShown = true;
notificationManager.notify(
com.android.internal.R.string.adb_active_notification_title,
mAdbNotification);
}
}
} else if (mAdbNotificationShown) {
//…省略部分代码
mAdbNotificationShown = false;
notificationManager.cancel(
com.android.internal.R.string.adb_active_notification_title);
}
}
}
症状：当插上 USB 线与 PC 相连再拔掉时，才显示“ USB Debugging connected ”
分析：通过上述介绍的代码搜索，只有 NotificationManagerService.java 才会出现此提示，也就是说只要当监测到用户修改Settings 中的设置值时和接收到 intent （即 usb 插拔充电）时才会调用 updateAdbNotification() 函数：
D/NotificationService( 1557): mBatteryPlugged = 1 D/NotificationService( 1557): 2. mBatteryPlugged = 1 D/NotificationService( 1557): mBatteryPlugged = 1 D/NotificationService( 1557): 2. mBatteryPlugged = 1 D/NotificationService( 1557): mBatteryPlugged = 2 D/NotificationService( 1557): 2. mBatteryPlugged = 2 D/NotificationService( 1557): adb enabled, Battery Plugged usb D/NotificationService( 1557): adb show notification D/NotificationService( 1557): mBatteryPlugged = 0 D/NotificationService( 1557): 2. mBatteryPlugged = 0 D/NotificationService( 1557): adb cancel notification D/NotificationService( 1557): mBatteryPlugged = 0 D/NotificationService( 1557): 2. mBatteryPlugged = 0
D/NotificationService( 1557): mBatteryPlugged=1 D/NotificationService( 1557): 2. mBatteryPlugged=1 D/NotificationService( 1557): mBatteryPlugged=1 D/NotificationService( 1557): 2. mBatteryPlugged=1 D/NotificationService( 1557): mBatteryPlugged=2 D/NotificationService( 1557): 2. mBatteryPlugged=2 D/NotificationService( 1557): adb enabled, Battery Plugged usb D/NotificationService( 1557): adb show notification D/NotificationService( 1557): mBatteryPlugged=0 D/NotificationService( 1557): 2. mBatteryPlugged=0 D/NotificationService( 1557): adb cancel notification D/NotificationService( 1557): mBatteryPlugged=0 D/NotificationService( 1557): 2. mBatteryPlugged=0
结合 log 看出， mBatteryPlugged 在usb线连上时 为 1 （即 BATTERY_PLUGGED_AC ，不是2即BatteryManager.BATTERY_PLUGGED_USB ）而不能进入，在拔掉瞬间为 2 ，则发出提示；在拔掉之后为0。
mBatteryPlugged 的值来自于 Intent ：
mBatteryPlugged = intent.getIntExtra( "plugged" , 0 );
updateAdbNotification();
mBatteryPlugged = intent.getIntExtra("plugged", 0);
updateAdbNotification();
它发起于下面代码（见文件 frameworks/base/services/java/com/android/server/ BatteryService.java ）
private synchronized final void update() {
native_update();//JNI层去读取各种值
boolean logOutlier = false ;
long dischargeDuration = 0;
mBatteryLevelCritical = mBatteryLevel <= CRITICAL_BATTERY_LEVEL;
if (mAcOnline) {
mPlugType = BatteryManager.BATTERY_PLUGGED_AC;
} else if (mUsbOnline) {
mPlugType = BatteryManager.BATTERY_PLUGGED_USB;
} else {
mPlugType = BATTERY_PLUGGED_NONE;
}
private synchronized final void update() {
native_update();//JNI层去读取各种值
boolean logOutlier = false;
long dischargeDuration = 0;
mBatteryLevelCritical = mBatteryLevel <= CRITICAL_BATTERY_LEVEL;
if (mAcOnline) {
mPlugType = BatteryManager.BATTERY_PLUGGED_AC;
} else if (mUsbOnline) {
mPlugType = BatteryManager.BATTERY_PLUGGED_USB;
} else {
mPlugType = BATTERY_PLUGGED_NONE;
}
在文件中 com_android_server_BatteryService.cpp 中，函数：
static void android_server_BatteryService_update(JNIEnv* env, jobject obj)
static void android_server_BatteryService_update(JNIEnv* env, jobject obj)
会从 sys 系统下读取需要的值：
#define AC_ONLINE_PATH "/sys/class/power_supply/ac/online" #define USB_ONLINE_PATH "/sys/class/power_supply/usb/online" #define BATTERY_STATUS_PATH "/sys/class/power_supply/battery/status" #define BATTERY_HEALTH_PATH "/sys/class/power_supply/battery/health" #define BATTERY_PRESENT_PATH "/sys/class/power_supply/battery/present" #define BATTERY_CAPACITY_PATH "/sys/class/power_supply/battery/capacity" #define BATTERY_VOLTAGE_PATH "/sys/class/power_supply/battery/batt_vol" #define BATTERY_TEMPERATURE_PATH "/sys/class/power_supply/battery/batt_temp" #define BATTERY_TECHNOLOGY_PATH "/sys/class/power_supply/battery/technology"
#define AC_ONLINE_PATH "/sys/class/power_supply/ac/online" #define USB_ONLINE_PATH "/sys/class/power_supply/usb/online" #define BATTERY_STATUS_PATH "/sys/class/power_supply/battery/status" #define BATTERY_HEALTH_PATH "/sys/class/power_supply/battery/health" #define BATTERY_PRESENT_PATH "/sys/class/power_supply/battery/present" #define BATTERY_CAPACITY_PATH "/sys/class/power_supply/battery/capacity" #define BATTERY_VOLTAGE_PATH "/sys/class/power_supply/battery/batt_vol" #define BATTERY_TEMPERATURE_PATH "/sys/class/power_supply/battery/batt_temp" #define BATTERY_TECHNOLOGY_PATH "/sys/class/power_supply/battery/technology"
其中前 2 项标明了是 AC 还是 USB 充电。
因此，问题产生在系统底层识别 usb 充电信息错误，导致错误的时刻去显示 USB Debugging connect 信息。
总结：
当系统的 BatteryService （ BatteryService.java ）调用 JNI 层（ com_android_server_BatteryService.cpp ），通过 sys 系统文件获得充电（如 usb 充电）及电池信息，然后通过 intent 发送出去。 NotificationManagerService.java 在接收到广播信息后，分析是 usb 充电则采取相应的提示信息。
另外， NotificationManagerService 还监听着 Settings 里用户是否修改了设置的值，采取相应动作（是否更新提示信息、是否停掉或开启 adbd 守护进程等）。