安卓 WIFI设置静态IP 出现的问题

先发一个链接是我参考的代码
http://blog.csdn.net/zyp009/article/details/21242073

基本就是拿过来用 里面调用的函数都没碰

public void StartWifiStaticIP() {
    WifiManager wifiManager = (WifiManager) getActivity().getSystemService(Context.WIFI_SERVICE);
    WifiConfiguration wifiConfig = null;
    WifiInfo connectionInfo = wifiManager.getConnectionInfo();  //得到连接的wifi网络
    List<WifiConfiguration> config_static = wifiManager.getConfiguredNetworks();
    for (WifiConfiguration conf : config_static)
        if (conf.networkId == connectionInfo.getNetworkId()) {
            wifiConfig = conf;
            break;
        }
    if (wifiConfig == null) return;
    Log.e("StartWifiStaticIP", "wifiConfig=" + wifiConfig.toString());
    try {
        setIpAssignment("STATIC", wifiConfig);
        setIpAddress(InetAddress.getByName("192.168.1.110"), 24, wifiConfig);
        setGateway(InetAddress.getByName("192.168.1.1"), wifiConfig);
        setDNS(InetAddress.getByName("202.96.64.77"), wifiConfig);
        wifiManager.updateNetwork(wifiConfig);
        wifiManager.enableNetwork(wifiConfig.networkId, false);
        wifiManager.enableNetwork(wifiConfig.networkId, true);
        wifiManager = null;
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (NoSuchMethodException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (java.lang.InstantiationException e) {
        e.printStackTrace();
    } catch (InvocationTargetException e) {
        e.printStackTrace();
    } catch (UnknownHostException e) {
        e.printStackTrace();
    }
}

    然后有几个问题 一个就是
      setIpAddress(InetAddress.getByName("192.168.1.110"), 24, wifiConfig);
        函数中的24是什么意思

        还有就是我设置了静态IP之后，重新获取当前IP地址网关等信息获取到的还是我没执行函数之前的IP地址，这时候我连一下别的WIFI再连接这个我设置的wifi获取的才是我执行函数后的IP地址。。这里是什么原因呢。。。
        还有就是IP地址的数值如果稍微大一点 如 192.168.1.180这样获取的IP地址是一个负数，求大神指点。。。

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