Connect android app to SQL Server

You can use SqlConnection:https://developer.xamarin.com/api/type/System.Data.SqlClient.SqlConnection/

using (SqlConnection connection = new SqlConnection(connectionString))    {        connection.Open();        // Do work here; connection closed on following line.    }

EDIT:This a method that I found in one of my libraries and I modified it a little bit. First you need to create a connection string so Xamarin knows where to connect. After that we create a SQL command using SqlCommand and then we executes it.

public void Execute(){    SqlConnectionStringBuilder dbConString = new SqlConnectionStringBuilder();    dbConString.UserID = "My Username";    dbConString.Password = "My Password";    dbConString.DataSource = "My Server Address";    using (SqlConnection con = new SqlConnection(returnConnectionString().ConnectionString))    {        con.Open();        for (int i = 0; i < commands.Count; i++)        {            SqlCommand cmd = new SqlCommand("UPDATE MyTable SET Name = 'New Name' WHERE ID = 1");            cmd.Connection = con;            cmd.ExecuteNonQuery();        }    }

ExecuteNonQuery() returns how many rows was affected so it's usuall used when for UPDATE- and INSERT-statements (i.e. not for SELECT-statements). More information:https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.executenonquery(v=vs.110).aspx }

If you are going to use a SELECT-statement this code returns the result as a DataSet:

public DataSet Execute(Statement stat){        DataSet ds = new DataSet();        SqlConnectionStringBuilder dbConString = new SqlConnectionStringBuilder();        dbConString.UserID = "My Username";        dbConString.Password = "My Password";        dbConString.DataSource = "My Server Address";        using (SqlConnection con = new SqlConnection(dbConString.ConnectionString))        {            con.Open();            SqlCommand cmd = new SqlCommand("SELECT * FROM MyTable", con);            var adapter = new SqlDataAdapter(cmd);            adapter.Fill(ds);        }        return ds;}