The implementation principle of slow charging and fast charging prompts in Android 8.0

<string name="keyguard_plugged_in" msg>"Recharge"</string>
  <string name="keyguard_plugged_in_charging_fast" msg>"Fast charging"</string>
  <string name="keyguard_plugged_in_charging_slowly" msg>"Slow charging"</string>

<!-- When the lock screen is showing and the phone plugged in, and the battery is not fully charged, and it's plugged into a fast charger, say that it's charging fast. --> 
<string name="keyguard_plugged_in_charging_fast">Charging rapidly</string>

<!-- When the lock screen is showing and the phone plugged in, and the battery is not fully charged, say that it's charging. --> 
<string name="keyguard_plugged_in">Charging</string>

<!-- When the lock screen is showing and the phone plugged in, and the battery is not fully charged, and it's plugged into a slow charger, say that it's charging slowly. --> 
<string name="keyguard_plugged_in_charging_slowly">Charging slowly</string>

•public static final String EXTRA_MAX_CHARGING_CURRENT = “max_charging_current”;
•public static final String EXTRA_MAX_CHARGING_VOLTAGE = “max_charging_voltage”;

frameworks/base/services/core/java/com/android/server/
// Send battery broadcast eventprivate void sendIntentLocked() {
  // Pack up the values and broadcast them to everyone
  final Intent intent = new Intent(Intent.ACTION_BATTERY_CHANGED);
  (Intent.FLAG_RECEIVER_REGISTERED_ONLY
      | Intent.FLAG_RECEIVER_REPLACE_PENDING);
.......
(BatteryManager.EXTRA_MAX_CHARGING_CURRENT, );
(BatteryManager.EXTRA_MAX_CHARGING_VOLTAGE, );

adb shell cat /sys/class/power_supply/battery/current_max
adb shell cat /sys/class/power_supply/battery/current_max
30000001

adb shell cat /sys/class/power_supply/battery/voltage_max
adb shell cat /sys/class/power_supply/battery/voltage_max
50000001

system/core/healthd/
#define POWER_SUPPLY_SYSFS_PATH "/sys/class/" POWER_SUPPLY_SUBSYSTEM
("%s/%s/voltage_max", POWER_SUPPLY_SYSFS_PATH,mChargerNames[i].string());

private final BroadcastReceiver mBroadcastReceiver = new BroadcastReceiver() {
    ....
    } else if (Intent.ACTION_BATTERY_CHANGED.equals(action)) {
        final int status = (EXTRA_STATUS, BATTERY_STATUS_UNKNOWN);
        final int plugged = (EXTRA_PLUGGED, 0);
        final int level = (EXTRA_LEVEL, 0);
        final int health = (EXTRA_HEALTH, BATTERY_HEALTH_UNKNOWN);
        final int maxChargingMicroAmp = (EXTRA_MAX_CHARGING_CURRENT, -1);
        int maxChargingMicroVolt = (EXTRA_MAX_CHARGING_VOLTAGE, -1);
        final int maxChargingMicroWatt;
        if (maxChargingMicroVolt <= 0) {
          maxChargingMicroVolt = DEFAULT_CHARGING_VOLTAGE_MICRO_VOLT;
        }
        if (maxChargingMicroAmp > 0) {
          // Calculating muW = muA * muV / (10^6 mu^2 / mu); splitting up the divisor
          // to maintain precision equally on both factors.
          maxChargingMicroWatt = (maxChargingMicroAmp / 1000)
              * (maxChargingMicroVolt / 1000);
        } else {
          maxChargingMicroWatt = -1;
        }
        final Message msg = (
            MSG_BATTERY_UPDATE, new BatteryStatus(status, level, plugged, health,
                maxChargingMicroWatt));
        (msg);

protected class BaseKeyguardCallback extends KeyguardUpdateMonitorCallback {
    public static final int HIDE_DELAY_MS = 5000;
    private int mLastSuccessiveErrorMessage = -1;
    @Override
    public void onRefreshBatteryInfo( status) {
      boolean isChargingOrFull =  == BatteryManager.BATTERY_STATUS_CHARGING
          ||  == BatteryManager.BATTERY_STATUS_FULL;
      boolean wasPluggedIn = mPowerPluggedIn;
      mPowerPluggedIn = () && isChargingOrFull;
      mPowerCharged = ();
      mChargingWattage = ;
      mChargingSpeed = (mSlowThreshold, mFastThreshold);
      updateIndication();
      if (mDozing) {
        if (!wasPluggedIn && mPowerPluggedIn) {
          showTransientIndication(computePowerIndication());
          hideTransientIndicationDelayed(HIDE_DELAY_MS);
        } else if (wasPluggedIn && !mPowerPluggedIn) {
          hideTransientIndication();
        }
      }
    }
=====================================================================================================
  public static class BatteryStatus {
    public static final int CHARGING_UNKNOWN = -1;
    public static final int CHARGING_SLOWLY = 0;
    public static final int CHARGING_REGULAR = 1;
    public static final int CHARGING_FAST = 2;
    public final int status;
    public final int level;
    public final int plugged;
    public final int health;
    public final int maxChargingWattage;
    public BatteryStatus(int status, int level, int plugged, int health,
        int maxChargingWattage) {
       = status;
       = level;
       = plugged;
       = health;
       = maxChargingWattage;
    }
  public final int getChargingSpeed(int slowThreshold, int fastThreshold) {
    return maxChargingWattage <= 0 ? CHARGING_UNKNOWN :
        maxChargingWattage < slowThreshold ? CHARGING_SLOWLY :
        maxChargingWattage > fastThreshold ? CHARGING_FAST :
        CHARGING_REGULAR;
  }

frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/
    int chargingId;
    switch (mChargingSpeed) {
      case .CHARGING_FAST:
        chargingId = hasChargingTime
            ? .keyguard_indication_charging_time_fast
            : .keyguard_plugged_in_charging_fast;
        break;
      case .CHARGING_SLOWLY:
        chargingId = hasChargingTime
            ? .keyguard_indication_charging_time_slowly
            : .keyguard_plugged_in_charging_slowly;
        break;
      default:
        chargingId = hasChargingTime
            ? .keyguard_indication_charging_time
            : .keyguard_plugged_in;
        break;
    }