如何在Android中切换主机

Question

I'm trying to access ESP8266 over internet and from LAN, and i'm using no-ip to get connected over internet but if i have no internet connection i can not access ESP8266 so i have to connect to LAN if there is no internet connection. I read forums here and almost tried all but unable to access ESP8266 through LAN.

String address = "mynoipdomain"; //global variable
String lan = "myesplocalip"; // global variable

String serverAdress;
ConnectivityManager connectivityManager = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
    assert connectivityManager != null; //i added this line because Android Studio was giving warning that "Method invocation 'getNetworkInfo' may produce 'java.lang.NullPointerException'"
    if(connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_MOBILE).getState() == NetworkInfo.State.CONNECTED ||
            connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_WIFI).getState() == NetworkInfo.State.CONNECTED) {
        serverAdress = address + ":3001"; //3001 is port
    }
    else{
        serverAdress = lan + ":3001";
    }

Answer 1

the if condition probably should be:

String bssid = getCurrentSsid(getContext());

if(bssid != null && bssid.equals("HOME_BSSID")) {
    serverAdress = lan + ":3001";
} else if(connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_WIFI).getState() == NetworkInfo.State.CONNECTED || connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_MOBILE).getState() == NetworkInfo.State.CONNECTED) {
    serverAdress = address + ":3001";
} else {
    // both networks are offline
}

combined with this method ( source ):

public String getCurrentSsid(Context context) {
    String ssid = null;
    ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = cm.getActiveNetworkInfo();
    if (networkInfo == null) {
        return null;
    }

    if (networkInfo.isConnected()) {
        final WifiManager wifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
        final WifiInfo connectionInfo = wifiManager.getConnectionInfo();
        if (connectionInfo != null && !StringUtil.isBlank(connectionInfo.getSSID())) {
            ssid = connectionInfo.getSSID();
        }
    }
    return ssid;
}

in order to prefer the local IP, when the home WiFi is connected.