Platform: Rockchip
OS: Android 6.0
Kernel: 3.10.92

開發者選項有個欄位是“Aggressive WiFi to Cellular handover”，

這個選項的功能是“當WiFi訊號較弱時，將主動從WiFi切換到移動資料網路”，根據之前對網路評分機制的瞭解，當WiFi分數較低的時候，那麼就會被“踢出局”由移動資料網路接替工作，那麼此選項是否也是通過影響評分值的方式呢？

“Aggressive WiFi to Cellular handover”對應的string name在

packages/apps/Settings/res/values/strings.xml:3643:
<string name="wifi_aggressive_handover">Aggressive Wi\u2011Fi to Cellular handover</string>

程式碼裡查詢wifi_aggressive_handover
DevelopmentSettings.java
private static final String WIFI_AGGRESSIVE_HANDOVER_KEY = "wifi_aggressive_handover";
mWifiAggressiveHandover = findAndInitSwitchPref(WIFI_AGGRESSIVE_HANDOVER_KEY);
當點選設定裡的switch時，觸發click函式

public boolean onPreferenceTreeClick()
{
    } else
 
 if (preference == mWifiAggressiveHandover) {
        writeWifiAggressiveHandoverOptions();
    } 
}

writeWifiAggressiveHandoverOptions()

private void writeWifiAggressiveHandoverOptions() {
    mWifiManager.enableAggressiveHandover(mWifiAggressiveHandover.isChecked() ? 1 : 0);
}

最終呼叫WiFiService

public
 
 void enableAggressiveHandover(int enabled) {
    enforceAccessPermission();
    mWifiStateMachine.enableAggressiveHandover(enabled);
}

void enableAggressiveHandover(int enabled) {
    mAggressiveHandover = enabled;
}

mAggressiveHandover被呼叫的地方：

private void calculateWifiScore(WifiLinkLayerStats stats) {
    //rssi受mAggressiveHandover的值影響
    int rssi = mWifiInfo.getRssi() - 6 * mAggressiveHandover
            + (homeNetworkBoost ? WifiConfiguration.HOME_NETWORK_RSSI_BOOST : 0);
    sb.append(String.format(" rssi=%d ag=%d", rssi, mAggressiveHandover));

    boolean isBadRSSI = (is24GHz && rssi < mWifiConfigStore.thresholdBadRssi24.get())
            || (!is24GHz && rssi < mWifiConfigStore.thresholdBadRssi5.get());
    boolean isLowRSSI = (is24GHz && rssi < mWifiConfigStore.thresholdLowRssi24.get())
            || (!is24GHz && mWifiInfo.getRssi() < mWifiConfigStore.thresholdLowRssi5.get());
    boolean isHighRSSI = (is24GHz && rssi >= mWifiConfigStore.thresholdGoodRssi24.get())
            || (!is24GHz && mWifiInfo.getRssi() >= mWifiConfigStore.thresholdGoodRssi5.get());
}

可以看到當此選項開啟之後，rssi的值會變小，進而影響到到score的值，印證了一開始的猜測

不過這種做法讓人費解，相當於強制在程式碼中減少實際RSSI的值，然後讓WiFi強制切換到行動網路，不太理解Google的做法