How to configure a static IP address, netmask, gateway programmatically on Android 3.x or 4.x

I realise that there is no API on 3.x or 4.x for those setting per SSID. Therefore, I checked out the source code and found out that the configuration of each SSID is stored in android.net.wifi.WifiConfiguration which is gotten from android.net.wifi.WifiManager.

In the below code, IpAssignment is an Enum, either STAIC, DHCP or NONE.
And linkProperties is the object store IP address, gateway, DNS, etc…

linkAddress is IP address and its netmask as prefixLength (how many bit 1 in netmask).

mRoutes is ArrayList of RouteInfo that can indicate gateway.

mDnses is ArrayList of InetAddress for DNS.

Firstly, get the current configuration using WifiConfiguration SSID

WifiConfiguration wifiConf = null;
WifiManager wifiManager = (WifiManager)getSystemService(Context.WIFI_SERVICE);
WifiInfo connectionInfo = wifiManager.getConnectionInfo();
List<WifiConfiguration> configuredNetworks = wifiManager.getConfiguredNetworks();        
for (WifiConfiguration conf : configuredNetworks){
    if (conf.networkId == connectionInfo.getNetworkId()){
        wifiConf = conf;
        break;              
    }
}

As the IpAssignment and linkProperties are hidden, the object can be gotten from reflection.

The following method can set the declared IP address setting on SSID WifiConfiguration:

    public static void setIpAssignment(String assign , WifiConfiguration wifiConf)
    throws SecurityException, IllegalArgumentException, NoSuchFieldException, IllegalAccessException{
        setEnumField(wifiConf, assign, "ipAssignment");     
    }

    public static void setIpAddress(InetAddress addr, int prefixLength, WifiConfiguration wifiConf)
    throws SecurityException, IllegalArgumentException, NoSuchFieldException, IllegalAccessException,
    NoSuchMethodException, ClassNotFoundException, InstantiationException, InvocationTargetException{
        Object linkProperties = getField(wifiConf, "linkProperties");
        if(linkProperties == null)return;
        Class laClass = Class.forName("android.net.LinkAddress");
        Constructor laConstructor = laClass.getConstructor(new Class[]{InetAddress.class, int.class});
        Object linkAddress = laConstructor.newInstance(addr, prefixLength);

        ArrayList mLinkAddresses = (ArrayList)getDeclaredField(linkProperties, "mLinkAddresses");
        mLinkAddresses.clear();
        mLinkAddresses.add(linkAddress);        
    }

    public static void setGateway(InetAddress gateway, WifiConfiguration wifiConf)
    throws SecurityException, IllegalArgumentException, NoSuchFieldException, IllegalAccessException, 
    ClassNotFoundException, NoSuchMethodException, InstantiationException, InvocationTargetException{
        Object linkProperties = getField(wifiConf, "linkProperties");
        if(linkProperties == null)return;
        Class routeInfoClass = Class.forName("android.net.RouteInfo");
        Constructor routeInfoConstructor = routeInfoClass.getConstructor(new Class[]{InetAddress.class});
        Object routeInfo = routeInfoConstructor.newInstance(gateway);

        ArrayList mRoutes = (ArrayList)getDeclaredField(linkProperties, "mRoutes");
        mRoutes.clear();
        mRoutes.add(routeInfo);
    }

    public static void setDNS(InetAddress dns, WifiConfiguration wifiConf)
    throws SecurityException, IllegalArgumentException, NoSuchFieldException, IllegalAccessException{
        Object linkProperties = getField(wifiConf, "linkProperties");
        if(linkProperties == null)return;

        ArrayList<InetAddress> mDnses = (ArrayList<InetAddress>)getDeclaredField(linkProperties, "mDnses");
        mDnses.clear(); //or add a new dns address , here I just want to replace DNS1
        mDnses.add(dns); 
    }

    public static Object getField(Object obj, String name)
    throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException{
        Field f = obj.getClass().getField(name);
        Object out = f.get(obj);
        return out;
    }

    public static Object getDeclaredField(Object obj, String name)
    throws SecurityException, NoSuchFieldException,
    IllegalArgumentException, IllegalAccessException {
        Field f = obj.getClass().getDeclaredField(name);
        f.setAccessible(true);
        Object out = f.get(obj);
        return out;
    }  

    private static void setEnumField(Object obj, String value, String name)
    throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException{
        Field f = obj.getClass().getField(name);
        f.set(obj, Enum.valueOf((Class<Enum>) f.getType(), value));
    }

After that, I can set setting and update WifiConfiguration for this SSID.

    try{
        setIpAssignment("STATIC", wifiConf); //or "DHCP" for dynamic setting
        setIpAddress(InetAddress.getByName("192.168.0.100"), 24, wifiConf);
        setGateway(InetAddress.getByName("4.4.4.4"), wifiConf);
        setDNS(InetAddress.getByName("4.4.4.4"), wifiConf);
        wifiManager.updateNetwork(wifiConf); //apply the setting
            wifiManager.saveConfiguration(); //Save it
    }catch(Exception e){
        e.printStackTrace();
    }

Edit:
Sorry for I don’t check for Android 3.x device that have silmilar UI with Android 4.x.
In Android 3.x, the gateway is storted in mGateways of linkProperties.
mGateways is Arraylist of type InetAddress. Therefore, following should work in Android 3.x.

public static void setGateway(InetAddress gateway, WifiConfiguration wifiConf)
        throws SecurityException, IllegalArgumentException, NoSuchFieldException, IllegalAccessException, 
        ClassNotFoundException, NoSuchMethodException, InstantiationException, InvocationTargetException{
            Object linkProperties = getField(wifiConf, "linkProperties");
            if(linkProperties == null)return;
            ArrayList mGateways = (ArrayList)getDeclaredField(linkProperties, "mGateways");
            mGateways.clear();
            mGateways.add(gateway);
        }

Edit2: The methods setIpAddress, setGateway, setDNS should be inputted as InetAddress type.