当用户注册时，用户名检查不起作用-asp.net

Question

我想检查用户名是否已经存在于数据库中，如果是，错误信息会提示“用户名已存在”。现在我有这个代码，但它不工作。程序仍然接受用户名，即使它是从数据库中复制的。有人可以帮我出去吗？这里是我的整个注册码：

protected void Page_Load(object sender, EventArgs e) 
    { 
     if (IsPostBack) 
     { 
      SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["RegistrationConnectionString"].ConnectionString); 
      conn.Open(); 
      string checkuser = "select count(*) from UserData where Username = '" + txtUser.Text + "'"; 
      SqlCommand scm = new SqlCommand(checkuser, conn); 
      int temp = Convert.ToInt32(scm.ExecuteScalar().ToString()); 
      if (temp == 1) // check if user already exist. 
      { 
       Response.Write("User already existing"); 
      } 
      conn.Close(); 
     } 
    } 
    protected void btn_Registration_Click(object sender, EventArgs e) 
    { 
     try 
     { 
      SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["RegistrationConnectionString"].ConnectionString); 
      conn.Open(); 
      string insertQuery = "insert into UserData(Username,Firstname,Lastname,Email,Password,CustomerType,DeliveryAddress,Zip,ContactNumber)values(@Username,@Firstname,@Lastname,@Email,@Password,@CustomerType,@DeliveryAddress,@Zip,@ContactNumber)"; 
      SqlCommand scm = new SqlCommand(insertQuery, conn); 
      scm.Parameters.AddWithValue("@Username", txtUser.Text); 
      scm.Parameters.AddWithValue("@Firstname", txtFN.Text); 
      scm.Parameters.AddWithValue("@Lastname", txtLN.Text); 
      scm.Parameters.AddWithValue("@Email", txtEmail.Text); 
      scm.Parameters.AddWithValue("@Password", BusinessLayer.ShoppingCart.CreateSHAHash(txtPW.Text)); 
      scm.Parameters.AddWithValue("@CustomerType", RadioButtonList1.SelectedItem.ToString()); 
      scm.Parameters.AddWithValue("@DeliveryAddress", txtAddress.Text); 
      scm.Parameters.AddWithValue("@Zip", txtZip.Text); 
      scm.Parameters.AddWithValue("@ContactNumber", txtContact.Text); 

      scm.ExecuteNonQuery(); 
      Session["Contact"]= txtContact.Text; 
      Session["Email"] = txtEmail.Text; 
      Session["DeliveryAddress"] = txtAddress.Text; 
      label_register_success.Text = ("Registration Successful!"); 
      //Response.Redirect("Home.aspx"); 
      conn.Close(); 
     } 
     catch (Exception ex) 
     { 
      Response.Write("Error:" + ex.ToString()); 
     } 
    } 

Answer 1

您验证Page_Load上的数据？我想，你可以选择这些solusions

1. 你必须这样做，在btn_Registration_Click您插入 数据之前，或
2. 也许，你可以修改它在SP做，如果数据通过它扔消息是 重复，并在那里做检查。

它应该是这样的（根据技术方案1）

protected void Page_Load(object sender, EventArgs e) 
    { 
     if (IsPostBack) 
     { 
     } 
    } 
    protected void btn_Registration_Click(object sender, EventArgs e) 
    { 
     try 
     { 
      SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["RegistrationConnectionString"].ConnectionString); 
      conn.Open(); 
      string checkuser = "select count(*) from UserData where Username = '" + txtUser.Text + "'"; 
      SqlCommand scm = new SqlCommand(checkuser, conn); 
      int temp = Convert.ToInt32(scm.ExecuteScalar().ToString()); 
      if (temp > 0) // check if user already exist. 
      { 
       Response.Write("User already existing"); 
      } 
      else 
      { 
       string insertQuery = "insert into UserData(Username,Firstname,Lastname,Email,Password,CustomerType,DeliveryAddress,Zip,ContactNumber)values(@Username,@Firstname,@Lastname,@Email,@Password,@CustomerType,@DeliveryAddress,@Zip,@ContactNumber)"; 
       scm = new SqlCommand(insertQuery, conn); 
       scm.Parameters.AddWithValue("@Username", txtUser.Text); 
       scm.Parameters.AddWithValue("@Firstname", txtFN.Text); 
       scm.Parameters.AddWithValue("@Lastname", txtLN.Text); 
       scm.Parameters.AddWithValue("@Email", txtEmail.Text); 
       scm.Parameters.AddWithValue("@Password", BusinessLayer.ShoppingCart.CreateSHAHash(txtPW.Text)); 
       scm.Parameters.AddWithValue("@CustomerType", RadioButtonList1.SelectedItem.ToString()); 
       scm.Parameters.AddWithValue("@DeliveryAddress", txtAddress.Text); 
       scm.Parameters.AddWithValue("@Zip", txtZip.Text); 
       scm.Parameters.AddWithValue("@ContactNumber", txtContact.Text); 

       scm.ExecuteNonQuery(); 
       Session["Contact"]= txtContact.Text; 
       Session["Email"] = txtEmail.Text; 
       Session["DeliveryAddress"] = txtAddress.Text; 
       label_register_success.Text = ("Registration Successful!"); 
       //Response.Redirect("Home.aspx"); 
      } 
      conn.Close(); 
     } 
     catch (Exception ex) 
     { 
      Response.Write("Error:" + ex.ToString()); 
     } 
    }