Question

我想问。如果在文本框中输入的值在MSSQL数据库中不可用，如何显示消息？我希望用户通知他们输入的值是否存在于数据库中。这是我目前的编码：

private void textBoxEmplNo_KeyUp(object sender, KeyEventArgs e)
    {
        if (e.KeyCode == Keys.Enter)
        {
            if (textBoxEmplNo.Text != "")
            {

                //Do something
                textBoxWorkNo.Text = dataGridView1.SelectedRows[0].Cells[2].Value.ToString();
                textBoxName.Text = dataGridView1.SelectedRows[0].Cells[0].Value.ToString();


                string selectSql = "select icnum, passport, deptno, section from m_employee where empno=@empno";
                SqlCommand cmd = new SqlCommand(selectSql, con);
                cmd.Parameters.AddWithValue("@empno", textBoxEmplNo.Text);

                try
                {
                    con.Open();

                    using (SqlDataReader read = cmd.ExecuteReader())
                    {
                        while (read.Read())
                        {
                            textBoxICPass.Text = (read["icnum"].ToString());
                            textBoxPassport.Text = (read["passport"].ToString());
                            textBoxDept.Text = (read["deptno"].ToString());
                            textBoxSection.Text = (read["section"].ToString());


                        }
                    }
                }
                finally
                {
                    con.Close();
                }

            }

            else
            {
                textBoxWorkNo.Text = "";
                textBoxName.Text = "";
            }

            dataGridView1.Visible = false;
        }
    }

Answer 1

我认为布尔变量可以帮助您解决问题。如果是这样，修改后的try块将完成这项工作：

bool isDataFound = false;
try
{
   con.Open();
   using (SqlDataReader read = cmd.ExecuteReader())
   {
       while (read.Read())
       {
            isDataFound = true;
            // populate the text boxes here
       }
   }
   if(!isDataFound)
   {
      // Display message here that no values found
      lblError.Text ="No Data Found";
   }
}

工作原理：我们有一个初始化为false的布尔变量，如果是while循环，我们将它们更改为true。然后我们将检查该变量以确定执行时间与否。 if if not表示将根据需要显示消息;

HasRows类的只读属性SqlDataReader也可用于此类。在这种情况下，您不需要使用额外的布尔变量，如果读者至少有一行，则HasRows属性将为true。所以你也可以使用它。以下是该

的代码

try
{
   con.Open();
   using (SqlDataReader read = cmd.ExecuteReader())
   {
       if(!read.HasRows)
       {
            // Display message here that no values found
            lblError.Text ="No Data Found";
       }
       else
       {
            while (read.Read())
            {
                 // populate the text boxes here
            }

       }
   }
}

Answer 2

试试这个;

如果你有行read.HasRows返回true

                using (SqlDataReader read = cmd.ExecuteReader())
                {
                    if (read.HasRows)
                    {
                        while (read.Read())
                        {
                            textBoxICPass.Text = (read["icnum"].ToString());
                            textBoxPassport.Text = (read["passport"].ToString());
                            textBoxDept.Text = (read["deptno"].ToString());
                            textBoxSection.Text = (read["section"].ToString());


                        }
                    }
                    else
                    {
                        lblError.Text = "No Data Found";
                    }
                }
            }

Answer 3

根据其他答案，您可以使用布尔值检查读取是否返回值，然后弹出一个消息框，提醒用户未找到记录。

例如：

using (SqlDataReader read = cmd.ExecuteReader())
                {
                    if (read.read())
                    {
                        //display values as you did before
                    }
                    else
                    {
                       //if using winform include System.Windows.Forms and use 
                       //  something like the following,
                       var result = MessageBox.Show(message, caption,
                                 MessageBoxButtons.YesNo,
                                 MessageBoxIcon.Question);

                      //depending on the result either cancel the request of prompt 
                        // user for another try.

                         //If using wpf

                     //  Include Windows.message.messagebox and use the message 
                     //  box class in a similar fashion as above.  Check usage if 
                     //  you are not familiar with it.
                    }
                }
            }

如果值不可用，则显示消息

3 个答案: