[RK3288][Android6.0] 主动从WLAN网络切换到移动数据网络

Platform: Rockchip

OS: Android 6.0

Kernel: 3.10.92

开发者选项有个栏位是“Aggressive WiFi to Cellular handover”，



这个选项的功能是“当WiFi信号较弱时，将主动从WiFi切换到移动数据网络”，根据之前对网络评分机制的了解，当WiFi分数较低的时候，那么就会被“踢出局”由移动数据网络接替工作，那么此选项是否也是通过影响评分值的方式呢？

“Aggressive WiFi to Cellular handover”对应的string name在

packages/apps/Settings/res/values/strings.xml:3643:

<string name="wifi_aggressive_handover">Aggressive Wi\u2011Fi to Cellular handover</string>

代码里查找wifi_aggressive_handover

DevelopmentSettings.java

private static final String WIFI_AGGRESSIVE_HANDOVER_KEY = "wifi_aggressive_handover";

mWifiAggressiveHandover = findAndInitSwitchPref(WIFI_AGGRESSIVE_HANDOVER_KEY);

当点击设置里的switch时，触发click函数

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

writeWifiAggressiveHandoverOptions()

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

最终调用WiFiService

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

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

mAggressiveHandover被调用的地方：

private void calculateWifiScore(WifiLinkLayerStats stats) {
//rssi受mAggressiveHandover的值影响
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());
}

可以看到当此选项开启之后，rssi的值会变小，进而影响到到score的值，印证了一开始的猜测

不过这种做法让人费解，相当于强制在代码中减少实际RSSI的值，然后让WiFi强制切换到移动网络，不太理解Google的做法