在调用"填充"之前,尚未初始化SelectCommand属性.在WinForm中

Question

我正在使用C#构建一个Windows应用程序.在我的登录表单中,我在调用fill方法之前没有初始化Select Command属性.

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);
        }
    }
}

Answer 1

在填充表之前,必须指定SqlDataAdapter的select命令.你没有这样做.您的SqlCommand对象未以任何方式连接到您的SqlDataAdapter.

 adp.SelectCommand=cmd;

Answer 2

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);