Question

我是wpf的新手正在处理项目，并且在没有数据时会收到无效尝试读取的错误我正在使用代码 -

        SqlConnection l_oConn=null;
        try
        {
            l_oConn = new SqlConnection("Data Source=ASHISH;Initial Catalog=iReg;Integrated Security=True");
            if (txt_userid.Text == "" || txt_password.Text == "")
            {
                MessageBox.Show("Please Enter the Id and Password", "Login Error");
                return;
            }
            else if (l_oConn.State == System.Data.ConnectionState.Closed) ;
            {
                l_oConn.Open();
            }
            SqlCommand l_oCmd = new SqlCommand("SELECT * FROM EmpLogin", l_oConn);
            SqlDataReader l_oDr = l_oCmd.ExecuteReader();
            int count = 0;
            while (l_oDr.HasRows)
            {
                l_oDr.Read();
                string ID, Password;
                ID = l_oDr.GetValue(0).ToString().Trim();
                Password = l_oDr.GetValue(1).ToString().Trim();
                if (ID == txt_userid.Text && Password == txt_password.Text)
                {
                    count = count + 1;
                    StRegistration strpage = new StRegistration();
                    this.NavigationService.Navigate(strpage);
                }
            }

            l_oDr.Close();
            if (count == 0)
            {
                MessageBox.Show("Please enter the Valid id and password", "Login Error");

            }

        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
        finally
        {
            if (l_oConn != null)
            {
                if (l_oConn.State == ConnectionState.Open)
                    l_oConn.Close();
                l_oConn.Dispose();
            }
        }

Answer 1

您需要至少读取一次datareader以从datareader获取行。所以从

更改代码

while(l_oDr.HasRows)
 {
    // Your logic
 }

到

 while (l_oDr.Read())
 {

 }

Answer 2

从

更改您的代码

       while (l_oDr.HasRows)
        {
            l_oDr.Read();
            string ID, Password;
            ID = l_oDr.GetValue(0).ToString().Trim();
            Password = l_oDr.GetValue(1).ToString().Trim();
            if (ID == txt_userid.Text && Password == txt_password.Text)
            {
                count = count + 1;
                StRegistration strpage = new StRegistration();
                this.NavigationService.Navigate(strpage);
            }
        }

到

        if (l_oDr.HasRows)
        {
            while(l_oDr.Read())
            {
               string ID, Password;
               ID = l_oDr.GetValue(0).ToString().Trim();
               Password = l_oDr.GetValue(1).ToString().Trim();
               if (ID == txt_userid.Text && Password == txt_password.Text)
               {
                  count = count + 1;
                  StRegistration strpage = new StRegistration();
                  this.NavigationService.Navigate(strpage);
               }
           }
        }

因为首先你应该检查DataReader中是否存在行，然后你应该循环遍历所有行。

当没有数据存在时，Winform无效尝试读取

2 个答案: