如何访问以编程方式添加的复选框

Question

I am developing an application in which i needed the to add filter. for that am adding checkbox programmatically because the filtering option are not predefine it depends on the value in the table to i add the checkbox as fallow

public void addCusineCheckbox()
{
            DataTable CusineList = Sql.ExecuteSelectCommand("select prod_group_id,Prod_group_name from Master_Prod_Groups");
            for (int i = 0; i < CusineList.Rows.Count; i++)
            {
                CheckBox chkCusine = new CheckBox();
                chkCusine.ID = "chk" + CusineList.Rows[i]["Prod_group_name"].ToString();
                chkCusine.Text = CusineList.Rows[i]["Prod_group_name"].ToString();
                divCusineFilter.Controls.Add(chkCusine);
            }
}

which help user to select the required field(there more other option to select) and then click on apply filter on that am try to access the that added check box as fallow

public string getCusineFilterString()
{

            string CusineID =null;
            DataTable CusineList = Sql.ExecuteSelectCommand("select prod_group_id,Prod_group_name from Master_Prod_Groups");
            for (int i = 0; i < CusineList.Rows.Count; i++)
            {
                CheckBox chk = (CheckBox)Page.FindControl("chk" + CusineList.Rows[i]["Prod_group_name"]);
                if (chk.Checked == true)
                {
                    if (i == 0)
                    {
                        CusineID = CusineList.Rows[i]["prod_group_id"].ToString();
                    }
                    else
                    {
                        CusineID = CusineID + "," + CusineList.Rows[i]["prod_group_id"].ToString();
                    }
                }
            }
            return CusineID;
}

but it gives the error that object not set to an instance.

i am not getting any idea to access to the checkbox.

Answer 1

There are certain limitations:

• You cannot access any controls in ASP.net which are not added before or on Init. So you can add the controls on Page OnInit, and then it will be accessible. But you have to be careful in adding the controls, so that they are added at right place and not duplicated.

• You should not write

  CheckBox chk = (CheckBox)Page.FindControl("chk");

instead write

var chkControl = Page.FindControl("chk");
if(chkControl != null /*&& check type*/) {
  CheckBox chk = (CheckBox)chkControl;
// and do something
}

• It will be better if you use CheckBoxList Control at design time and change the binding values to populate different check boxes at runtime

• Create check box(s) at design time and show hide based on user action.

Hope it helps

Answer 2

You can get the values using Request.Forms collection. It keeps the values of every control which is on the form. But it works on name rather than ID .

Get dynamic control (unique ID) on postback

The better approach is use empty CheckBoxList and add item at run-time.

Here is a link which has discussion on CheckBoxList
How can I get the CheckBoxList selected values, what I have doesn't seem to work C#.NET/VisualWebPart

Example

Create an empty

<asp:CheckBoxList ID="ChkBox1" runat="server"></asp:CheckBoxList>

And add items at runtime

 ChkBox1.Items.Add(new ListItem("Item 1", "Item1"));

And you can get data by using foreach loop as follow

  // Loop through each item.
    foreach (ListItem item in ChkBox1.Items)
    {
        if (item.Selected)
        {
            // If the item is selected, add the value to the list.

        }
        else
        {
            // Item is not selected, do something else.
        }
    }

Answer 3

You can add your checkboxes in Page_Load. I think the problem is in using Page.FindControl. Use divCusineFilter.FindControl rather than Page.FindControl and make sure that you add your checkboxes to page in postback too.