表中的动态复选框不会保留选中的值

Question

I am dynamically creating a table with data and check boxes in it, my problem is when i check to see one specific check-box is checked, out of many, it resets to the default state of false (note: its not just one it doesn't work with, it works with non of the generated check boxes)

Before i create the page_load function i create the check box, further down i create the table, and populate it with data, then i set up a function to check on a click to see if the box was indeed checked, iv'e tried many iterations of this with no luck

protected void  table_builder(SqlDataReader readerinfo)
{
    //Create a new step for the user
    step3label.Text = "3.";
    //Table header
    TableHeaderRow hr = new TableHeaderRow();
    TableHeaderCell hc = new TableHeaderCell();
    TableHeaderCell hc2 = new TableHeaderCell();
    TableHeaderCell hc3 = new TableHeaderCell();
    hr.Cells.Add(hc);
    hc.Text = "ID"; //Assign header 1 with a name
    hr.Cells.Add(hc2);
    hc2.Text = "Name";//Assign header 2 with a name
    hr.Cells.Add(hc3);
    hc3.Text = "Selection";
    Table1.Rows.Add(hr);


    //Dynamic Table Generation
    int numcells = 3;
    int triswitch = 0;//this is use to chose which cell is made, id, name or selection
    string checkboxID = null;


    while (readerinfo.Read())   //execute the following aslong as there is data to fill the table with
    {
        for (int j = 0; j < 1; j++)
        {
            TableRow r = new TableRow();
            for (int i = 0; i < numcells; i++)
            {
                TableCell c = new TableCell();

                switch (triswitch)
                {
                    case 0: // this case sets the info for the feild id
                        c.Text = readerinfo.GetSqlGuid(0).ToString();
                        checkboxID = readerinfo.GetSqlGuid(0).ToString();
                        r.Cells.Add(c);
                        triswitch = 1;
                        break;

                    case 1:
                        c.Text = readerinfo.GetString(1);
                        r.Cells.Add(c);
                        triswitch = 2;
                        break;

                    case 2:
                        Checkbox_creator(checkboxID,ref c);
                        r.Cells.Add(c);
                        triswitch = 0;
                        break;

                }
            }
            Table1.Rows.Add(r);
        }
    }       
}

protected void Checkbox_creator(string id,ref TableCell send)
{
    //create the checbox
    ckbx = new CheckBox();
    ckbx.ID = "CBX" + checkboxid.ToString();
    checkboxid++;
    ckbx.InputAttributes.Add("value", id);
    send.Controls.Add(ckbx); //add the chekbox to the cell
    checkboxidlist.Add(id);//add the id of the checkbox to the list 
}



//
//AFTER DATATABLE IS LOADED
//

public void test()
{
    // Find control on page.
    CheckBox myControl1 = (CheckBox)Table1.FindControl("CBX0");
    if (myControl1 != null)
    {
        // Get control's parent.
        Control myControl2 = myControl1.Parent.Parent.Parent;
        Response.Write("Parent of the text box is : " + myControl2.ID);
        if (myControl1.Checked == true)
        {
            Response.Write("check box checked");
        }
    }
    else
    {
        Response.Write("Control not found");
    }
}
 //on Submit button click, execute the following function
protected void Submit_Click(object sender, EventArgs e)
{
    //Code to be executed
    string Userinput; //declare Userinput variable
    Userinput = Searchbox.Value; // Set variable to asp controll        
    Response.Write("<br /> <br />"+ Userinput +" <- user imput works");
    ConnectToSql(Userinput);//insert what the user submitted into a query
    test();
    //
    //
    //NoTe code validation is needed to prevent injections
    //  
}

Answer 1

So basically what is happening here is that you are dynamically dropping this onto the page every time the page loads. Because you are doing this dynamically, the checkbox that fires off a "checked" event or is checked against during a postback no longer exists as it is not part of the viewstate. The way that the ASP.NET page lifecycle works is to fire off the sequence of lifecycle events regardless of whether or not the page is posted back or not, meaning that a new page is built upon you firing a postback event and the page goes through preinit, init, preload, load, and all that jazz before it actually hits any of the event handling code. The page that exists for the postback has a freshly created set of checkboxes that have no binding to the ones that were on the previous page.

You have a few options here, and here are two of them:

Have the 'checked' event fire a postback and have the unique ID of the web control checked against a collection you maintain on the server. You can drop the controls onto the page via a repeater or gridview and hook into its populate event. In doing so you can add the unique ID of the control that was just added into a Dictionary that you store in session that maintains any relationship that you want from a checkbox to a piece of data.

Use Javascript to update a hidden field that is always on the page and has view state enabled. In doing so you can have some sort of delimited string containing the information you deem relevant to the 'checked' checkboxes. Every time a checkbox is checked, add its identifying information to the hidden input field's value and then when the postback fires you should be able to check that hidden input for its value and do whatever you need to do from there.

These both seem like pretty hairy ways of handling this though. If you elaborate on what exactly you need then perhaps I can give you a better suggestion.

Answer 2

add the check boxes to the page before the view state is loaded and the event fires. Do it in the OnInit method not the onload. Use Onload to see if they're checked or not. Be sure you're giving them ID's. Unless this is a partial postback (ajax) then only render the check boxes if !IsPostback

Answer 3

It appears after two days of searching, i have found a pretty good solution that is much quicker and easier to understand than some others; It appears that as the other answers state, it is because of the page_load, however in this situation init is not needed, you simply need to recreate all of the controls before you can do anything else.

The key to this solution is:

protected void RecreatePreviousState()
{
    if (this.IsPostBack)
    {
        //code to recreate
    }       
}

Where the comment in the above code is, is where you call the main function that creates all of your controls, like in my example it was:
ConnectToSql(Searchbox.Value) below will be all of the code associated with this page, for future reference for anyone with this problem.

Code Behind:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Data;


public partial class codebehind : System.Web.UI.Page 
{
//DECLARATIONS    
string selectedvalue;
List<string> createdckbxs = new List<string>();
List<string> CheckedCheckboxes = new List<string>();
CheckBox ckbx;
int ckbxID = 0;
//END DECLARATIONS


protected void Page_Load(object sender, EventArgs e)
{

    Response.Write(DateTime.Now); //local time -- testing
    Response.Write("<br /><br />NOTE: the id feild in the below table will be useless soon, it is only for testing purposes, look at CRM<br /><br />");
    selectedvalue = Request.QueryString["filter"];
    //88888888888888888
    RecreatePreviousState();
    //88888888888888888
    Response.Write(selectedvalue);
    instructionsfunc();
}


protected void instructionsfunc()
{
    switch (selectedvalue)
    {
        case "Name":
            instructions.Text = "Please enter the first few letters of the company you are looking for, ex. for "some company", you might search som";
            break;
        case "State":
            instructions.Text = "Please enter the abreviation of the state you are looking for, ex. for New York, enter NY";
            break;
    }

}


protected string sqlSelector(string uinput)
{
    switch (selectedvalue) //create the sql statments
    {
        case "Name":          
            return "SELECT [id],[name] FROM [asd].[jkl] WHERE [name] LIKE '" + uinput + "%' and [deleted] = 0 ORDER BY [name] ASC";  
        case "State":
            return "SELECT [id],[name] FROM [asd].[jkl] WHERE [shipping_address_state] LIKE '" + uinput + "%' and [deleted] = 0 ORDER BY [name] ASC";
        default:
            Response.Redirect("errorpage.aspx?id=002");
            return null; 
    }

}



//on Submit button click, execute the following function NOTE THIS BUTTON's ONLY USE IS POSTBACK
protected void Submit_Click(object sender, EventArgs e)
{
    string Userinput; //declare Userinput variable
    Userinput = Searchbox.Value; // Set variable to asp controll        
    Response.Write("<br /> <br />"+ Userinput +" <- user imput works");
}

//on Clear button click execute the following function
protected void Clear_Click(object sender, EventArgs e)
{
    Response.Redirect(Request.RawUrl);
}



protected void ConnectToSql(string input)
{
    System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection();
    //Todo add any aditional data needed to connection
    conn.ConnectionString = ConfigurationManager.ConnectionStrings["SplendidTestConnectionString"].ConnectionString;
    try
    {
        conn.Open();

        //this is the actual sql, this gets the data
        SqlCommand sqlString2 = new SqlCommand();
        sqlString2.CommandText = sqlSelector(input);
        sqlString2.CommandTimeout = 15;
        sqlString2.CommandType = System.Data.CommandType.Text;
        sqlString2.Connection = conn;
        SqlDataReader reader;
        reader = sqlString2.ExecuteReader();

        table_builder(reader);


        reader.Close(); //close the sql data reader



    }
    catch (Exception e)
    {
        //Some sort of redirect should go here to prevent the user from vewing a broken page
        conn.Close();
        //Response.Redirect("errorpage.aspx?id=001");
        Response.Write(e);
    }
    finally
    {
        if (conn.State != System.Data.ConnectionState.Closed)
        {
            conn.Close();//close up the connection after all data is done being populated
        }
    }

}

protected void  table_builder(SqlDataReader readerinfo)
{
    //Create a new step for the user
    step3label.Text = "3.";
    //Table header
    TableHeaderRow hr = new TableHeaderRow();
    TableHeaderCell hc = new TableHeaderCell();
    TableHeaderCell hc2 = new TableHeaderCell();
    TableHeaderCell hc3 = new TableHeaderCell();
    hr.Cells.Add(hc);
    hc.Text = "ID"; //Assign header 1 with a name
    hr.Cells.Add(hc2);
    hc2.Text = "Name";//Assign header 2 with a name
    hr.Cells.Add(hc3);
    hc3.Text = "Selection";
    Table1.Rows.Add(hr);


    //Dynamic Table Generation
    int numcells = 3;
    int triswitch = 0;//this is use to chose which cell is made, id, name or selection


    while (readerinfo.Read())   //execute the following aslong as there is data to fill the table with
    {
        for (int j = 0; j < 1; j++)
        {
            TableRow r = new TableRow();
            for (int i = 0; i < numcells; i++)
            {
                TableCell c = new TableCell();

                switch (triswitch)
                {
                    case 0: // this case sets the info for the feild id
                        c.Text = readerinfo.GetSqlGuid(0).ToString();
                        //RENAME THIS To ADDING BUTTON = readerinfo.GetSqlGuid(0).ToString();
                        r.Cells.Add(c);
                        triswitch = 1;
                        break;

                    case 1:
                        c.Text = readerinfo.GetString(1);
                        r.Cells.Add(c);
                        triswitch = 2;
                        break;

                    case 2:
                        ckbx = new CheckBox();
                        ckbx.ID = "CBX" + ckbxID;
                        createdckbxs.Add(ckbx.ID);
                        c.Controls.Add(ckbx);                           
                        r.Cells.Add(c);
                        triswitch = 0;
                        ckbxID++;
                        break;

                }
            }
            Table1.Rows.Add(r);
        }
    }
}



//
//AFTER DATATABLE IS LOADED
//   

protected void RecreatePreviousState()
{
    if (this.IsPostBack)
    {
        ConnectToSql(Searchbox.Value);
        MergeBtnCreate();
    }       
}

protected void MergeBtnCreate()
{
    Button MergeBTN = new Button();
    MergeBTN.Text = "Merge";
    MergeBTN.Click += new EventHandler(MergeBTN_Click);
    MergeBTNHolder.Controls.Add(MergeBTN);
}

void MergeBTN_Click(object sender, EventArgs e)
{
    foreach(string id in createdckbxs)
    {
        CheckBox myControl1 = (CheckBox)Table1.FindControl(id);
        if (myControl1 != null)
        {
            if (myControl1.Checked == true)
            {
                CheckedCheckboxes.Add(id);
            }
        }
        else
        {
            Response.Redirect("errorpage.aspx?id=003");
        }
    }

}

}

Asp.net

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="codebehind.aspx.cs" Inherits="codebehind" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Hello</title>
</head>
<body>
<form id="form1" runat="server">
        <div style="background-color:#55aaff;margin-bottom:10px;padding:5px;">
        <h3 style="padding:2px;margin:0px;">
            2.
        </h3>
        <asp:Label ID="instructions" runat="server" />
        <asp:Label ID="buttonclicked" runat="server" />
        <br />       
        <input id="Searchbox" type="text" runat="server" />
        <br />
        <asp:Button ID="SubmitBTN" runat="server" OnClick="Submit_Click" Text="Submit" />
        <asp:Button ID="ClearBTN" runat="server" OnClick="Clear_Click" Text="Clear" />
    </div>
    <div>
        <h3 style="padding:2px;margin:0px;">
            <asp:Label ID="step3label" runat="server" Text=""></asp:Label>
        </h3>
        <asp:Table ID="Table1" runat="server" GridLines="Both" />
    </div>
    <div>
        <asp:PlaceHolder ID="MergeBTNHolder" runat="server"></asp:PlaceHolder>
    </div>


</form>

</body>
</html>