使用 findcontrol 查找 gridview 中的值，并将其与数据库中的数据进行比较

Question

 protected void LinkButton_Click(Object sender, EventArgs e)
    {
        String MyConnection2 = "Server=localhost;database=ovs;Uid=root;password=; Convert Zero Datetime=True";
        DateTime time = DateTime.Now;              // Use current time
        string format = "yyyy-MM-dd HH:mm:ss";
        string UserName4 = HttpContext.Current.User.Identity.Name;
        GridViewRow grdrow = (GridViewRow)((LinkButton)sender).NamingContainer;
        Label lblStudentId = (Label)grdrow.Cells[0].FindControl("lblID");
        string studentId = lblStudentId.Text;
        String query = "insert into voting (CandidateStudentID,voterStudentID,DateTime)values ('" + lblStudentId.Text + "','" + Session["UserName"].ToString() + "','" + time.ToString(format) + "')";
        foreach (GridViewRow row in GridView2.Rows)
        {
            Label lblVoter = row.FindControl("lblVoter") as Label;
            string voterID = lblVoter.Text;


            if (Session["UserName"].ToString().Equals(lblVoter.Text))
            {
                Label1.Text = "You voted before";

            }

        }
        MySqlConnection MyConn2 = new MySqlConnection(MyConnection2);
        MySqlCommand MyCommand2 = new MySqlCommand(query, MyConn2);
        MySqlDataReader MyReader2;
        MyConn2.Open();
        MyReader2 = MyCommand2.ExecuteReader();
        Label2.Text = "Thank you for You Vote";

    }


  <asp:GridView ID="GridView2" runat="server"  AutoGenerateColumns="False" Font-Size="Medium">
          <Columns>
          <asp:TemplateField HeaderText="Student ID">
  <ItemTemplate>
     <asp:Label ID="lblVoter" runat="server"   Width="150px"  Text='<%#Eval("voterStudentID") %>'/>
 </ItemTemplate>
 </asp:TemplateField>
              
          </Columns>
       </asp:GridView>


 protected void loadCandidate()
    {
        con.Open();
        MySqlCommand cmd = new MySqlCommand("select studentID ,name from candidate  ", con);
        MySqlDataReader dr = cmd.ExecuteReader();
        if (dr.HasRows == true)
        {
            GridView1.DataSource = dr;
            GridView1.DataBind();
            con.Close();

            con.Open();
            MySqlCommand cmd2 = new MySqlCommand("select voterStudentID from voting  ", con);
            MySqlDataReader dr2 = cmd2.ExecuteReader();

            GridView2.DataSource = dr2;
            GridView2.DataBind();
        }
    }

StudentID display in gridview2

我想防止在数据库中重复投票。现在我面临一个问题，当用户以 StudentID table 中的第一个用户身份登录时，即 1909404，当 1909404 已经存在于数据库中时，它将显示错误消息。但是当用户以StudentIDtable为1909362的第二个用户登录时，即使用户ID已经存在，也不会显示错误信息。只要数据库中存在用户 ID（这意味着他们之前投票过），我就想显示错误消息。

Answer 1

改成这样....

foreach (GridViewRow row in GridView2.Rows) {
  Label lblVoter = row.FindControl("lblVoter") as Label;
  if (Session["UserName"].ToString().Equals(lblVoter.Text)) {
    Label1.Text = "You voted before";
    return;
  }
}
// Since we looped through all the rows and did NOT find a match...
// Then they can vote 
MySqlConnection MyConn2 = new MySqlConnection(MyConnection2);
MySqlCommand MyCommand2 = new MySqlCommand(query, MyConn2);
MySqlDataReader MyReader2;
MyConn2.Open();
MyReader2 = MyCommand2.ExecuteReader();
Label2.Text = "Thank you for You Vote";

使用 findcontrol 查找 gridview 中的值，并将其与数据库中的数据进行比较

Find the value in gridview using findcontrol and comapre it with data in database

c#

asp.net

gridview

findcontrol