C# SelectCommand 属性在调用“Fill”之前尚未初始化。在 WinForm 中

The SelectCommand property has not been initialized before calling 'Fill'. in WinForm

提问by Kaushik27

I am building a windows application using C#. In my login form, I'm getting Select Command property has not been initialized before calling fill method.

我正在使用 C# 构建 Windows 应用程序。在我的登录表单中，我得到Select Command 属性在调用 fill 方法之前尚未初始化。

Here is the code:

这是代码：

public partial class frmlogin : Form
{
    SqlConnection con = new SqlConnection("Data Source=TH07L019;Initial Catalog=loginerror;Integrated Security=True");
    DataTable dt = new DataTable();
    SqlCommand cmd = new SqlCommand();
    SqlDataAdapter adp = new SqlDataAdapter();

    public frmlogin()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        cmd.Connection = con;
    }

    private void button1_Click(object sender, EventArgs e)
    {
        con.Open();
        cmd.CommandText = "select * from login where username='" + txt1.Text + "' and password='" + txt2.Text +"'";
        adp.Fill(dt);
        if (dt.Rows.Count > 0)
        {
            frmmain main = new frmmain();
            main.Show();
        }
        else
        {
            MessageBox.Show("Please enter correct name and passowrd", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
    }
}

采纳答案by Arie

You have to specify select command of SqlDataAdapter before filling your table. You are not doing it. Your SqlCommand object is not connected in any way to your SqlDataAdapter.

在填充表之前，您必须指定 SqlDataAdapter 的 select 命令。你不是在做。您的 SqlCommand 对象未以任何方式连接到您的 SqlDataAdapter。

 adp.SelectCommand=cmd;

回答by Helix

Another way to accomplish would be to simply pass the SQLCommand as an argument into your data adapter as follows -

另一种完成方法是简单地将 SQLCommand 作为参数传递到您的数据适配器中，如下所示 -

SqlCommand cmd = new SqlCommand();
SqlDataAdapter adp = new SqlDataAdapter(cmd);

回答by Priyank Raunak

SQL Data Adapter interacts with the data table. It is used to fill the Data Table from SQL Server DataBase. Before, filling the Data Table, the Data Adapter should know the command it is going to execute. So we have to fill the object of SQL Command Type i.e

SQL 数据适配器与数据表交互。它用于填充 SQL Server 数据库中的数据表。在填充数据表之前，数据适配器应该知道它要执行的命令。所以我们要填充SQL Command Type的对象即

SqlDataAdapter da = new SqlDataAdapter(cmd);

Here cmdis the object of SQL Command.

这cmd是 SQL 命令的对象。

Now, the Data Adapter will know which command to execute before filling the data table.

现在，数据适配器将在填充数据表之前知道要执行哪个命令。

回答by RanjithKanna

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace Employees_Details_Management_System
{
    public partial class ShowEmpDtlsFrm : Form
    {

        SqlConnection con = new SqlConnection(@"Data Source = (local); Initial Catalog = sp_emp; Integrated Security = True");

        public SqlCommand cmd { get; private set; }

        // private SqlCommand cmd;

        public ShowEmpDtlsFrm()
        {
            InitializeComponent();
        }

        private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
        {

        }

        private void Form1_Load(object sender, EventArgs e)
        {
            ShwEmpDtlsLbl.Text = "Employee Database Management";
            comboBox1.Text = "Click";
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {

        }
        public void DataGridChk()//Check if DataGrid is empty or not
        {
           if (dataGridView1.RowCount == 1)
            {
                dataGridView1.Visible = false;
                MessageBox.Show("The Given " + comboBox1.Text+ " is Invalid  \nEnter Valid " + comboBox1.Text);
            }
        }

        public void DbDataFetch(String Qry)//For Fetching data from database
        {
            SqlCommand cmd = new SqlCommand(Qry, con);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds, "emp");
            dataGridView1.DataSource = ds.Tables["emp"].DefaultView;
            DataGridChk();
        }

        public void SrchBtn_Click(object sender, EventArgs e)
        {
            try
            {
                if (comboBox1.Text == "Employee ID" || comboBox1.Text == "Department ID" || comboBox1.Text == "Manager ID")
                {
                    if (textBox1.Text != "")
                    {
                        con.Open();
                        dataGridView1.Visible = true;
                        if (comboBox1.Text == "Employee ID")
                        {
                            string Qry = "select * from emp where emp_id='" + textBox1.Text + "' ";
                            DbDataFetch(Qry);
                        }
                        else if (comboBox1.Text == "Department ID")
                        {
                            string Qry = "select * from emp where  dep_id='" + textBox1.Text + "'  ";
                            DbDataFetch(Qry);
                        }
                        else if (comboBox1.Text == "Manager ID")
                        {
                            string Qry = "select * from emp where manager_id='" + textBox1.Text + "' ";
                            DbDataFetch(Qry);
                        }
                        con.Close();
                    }
                    else
                    {
                        MessageBox.Show("Please Enter the ID...");
                    }
                }
                else
                {
                    MessageBox.Show("Choose Valid Option...");
                }
            }
            catch (System.Data.SqlClient.SqlException sqlException)
            {
                System.Windows.Forms.MessageBox.Show(sqlException.Message);
                con.Close();
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            EmpDtlsFrm edf = new EmpDtlsFrm();
            edf.Show();
            this.Hide();
        }
    }
}