Question

请帮帮我...过去两天我面临这个问题

我的连接类

public class Connection
{
    SqlConnection conn;
    SqlCommand cmd;

    public void connclose()
    {
        conn.Close();
    }

    public Connection()
    {
        SqlConnection conn = new SqlConnection(@"server=ADMIN-PC;database=sample;Integrated security=true");
        SqlCommand cmd = null;
    }

    public void nonquery(string qry)
    {
        conn.Open();
        cmd = new SqlCommand(qry, conn);
        cmd.ExecuteNonQuery();
        conn.Close();
    }
}

我的班级

public class Master
{
    Connection conn = new Connection();

    public void insert(string name, string place, string company, string post)
    {
        string qry = "insert into company values('" + name + "','" + place + "','" + company + "'.'" + post + "')";
        conn.nonquery(qry);
    }
}

我不是要求你为我调试代码...请指出错误是什么..我是初学者所以请...

Answer 1

这里的问题是你试图在构造函数中实例化Connection类的字段，而不是创建局部变量。因此，就范围而言，您隐藏了conn和cmd变量。

试试这个：

public Connection()
{
    conn = new SqlConnection(@"server=ADMIN-PC;database=sample;Integrated security=true");
    cmd = null;
}

Answer 2

试试这段代码

public class Connection
{
    SqlConnection conn;
    SqlCommand cmd;

    public void connclose()
    {
        conn.Close();
    }

    public Connection()
    {
        // initializing global variables
        conn = new SqlConnection(@"server=ADMIN-PC;database=sample;Integrated security=true");
        cmd = null;
    }

    public void nonquery(string qry)
    {
        conn.Open();
        cmd = new SqlCommand(qry, conn);
        cmd.ExecuteNonQuery();
        conn.Close();
    }
}

Answer 3

虽然已经选择了答案（这完全解决了这里的问题），但我仍然想发布使用SqlCommand参数的答案。

public class Connection
{
   SqlConnection conn;
   SqlCommand cmd;

   public void connclose()
   {
     conn.Close();
   }

   public Connection()
   {   
       conn = new SqlConnection(@"server=ADMIN-PC;database=sample;Integrated security=true");        
       cmd = null;
   }

   public void nonquery(string qry, string[] arrParams, string[] arrParamsVals)
   {          
      try
      {
          conn.Open();
          cmd = new SqlCommand(qry, conn);

          for(int i=0; i < arrParams.Length; i++)
             cmd.Paratmeters.AddWithValue(arrParams[i], arrParamsVals[i]);

          cmd.ExecuteNonQuery();

      }
      catch{}
      finally { conn.Close(); }          
   }
 }

大师班：

public class Master
{
    Connection conn = new Connection();

    public void insert(string name, string place, string company, string post)
    {
       string qry = "Insert into company values(@name, @place, @company, @post)";
       string[] arrParams= {"@name", "@place", "@company", "@post"};
       string[] arrParamsVals= {name, place, company, post};
       conn.nonquery(qry, arrParams, arrParamsVals);
    }
 }

对象引用未设置为对象的实例。（C＃Web应用程序）

3 个答案: