Question

So I am quite new to Android, and have limited previous Java experience, so please bear with me. I am trying to create an object of type WifiManager in an Android App, and I have the line I found several other people recommend to create a WifiManager object verbatum:

WifiManager wifi =  mContext.getSystemService(Context.WIFI_SERVICE);

in my program. Now Eclipse has underlined the mContext.GetSystemService etc part with the error Type mismatch, cannot convert from object to WifiManager

Now I have tried recasting the return using:

(WifiManager) mContext.getSystemService(Context.WIFI_SERVICE);

This will compile, but results in a java.lang.NullPointerException when executed

Any thoughts on this would be greatly appreciated!

UPDATE*

SO I have setup the

Context mContext; 

in my main class

Then I am trying to use a broadcast to find the address of a SQL server on my network. The code is kinda messy since I am just in the phase where I am trying to get just transmitting the broadcast to work. But here is the function.

public void findSQL()
{
    int PORT = 1433;

    try
    {
        byte buff[] = new byte[1024];
        DatagramSocket sock = new DatagramSocket(PORT); 
        sock.setBroadcast(true);

        // Create and send the broadcast packet
        DatagramPacket dp = new DatagramPacket(buff, 7, getBroadcastAddress(), PORT);

        sock.send(dp);

        DatagramPacket dp1 = new DatagramPacket(buff, buff.length);

        sock.receive(dp1);

        sock.close();
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
}
InetAddress getBroadcastAddress() throws IOException {  
    WifiManager wifi =  (WifiManager) mContext.getSystemService(Context.WIFI_SERVICE);
    DhcpInfo dhcp = wifi.getDhcpInfo();

    System.out.println(dhcp.toString());

    if(dhcp==null)
        return InetAddress.getByAddress(null);

    int broadcast = (dhcp.ipAddress & dhcp.netmask) | ~dhcp.netmask;

    byte[] quads = new byte[4];
    for (int k = 0; k < 4; k++)
    {
        quads[k] = (byte) ((broadcast >> k * 8) & 0xFF);
    }

    return InetAddress.getByAddress(quads);
}

SECOND EDIT*

Earlier in my code I have defined:

    @SuppressWarnings("unused")
class MSSQL_DB
{
    Context mContext;
    public void dbConnect(String db_connect_string, 
            String db_userid, String db_password)
    {
        try
        {
            Class.forName("net.sourceforge.jtds.jdbc.Driver");
            Connection conn = DriverManager.getConnection(db_connect_string,
                    db_userid, db_password);
            System.out.println("Connected");

        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }

I am afraid the whole concept of what “context” actually does, how to declare it correctly, and how to use its methods is what I must not be fully understanding yet.

Answer 1

Most probably ur mContext is null.. If not

Please post more logs of exception.. and post more code …