The main object of this article is to access value of dynamic asp.net controls which are generated conditionally. For this, we will save viewstate of dynamic controls.
Suppose we have one dropdown and one button. When user selects “Generate” option, the Dynamic table will be generated. In each cell of table there will be textbox. User enters value in the textboxes and click on button then it will display all user entered values.

<form id="form1" runat="server">
    <div>
        <asp:Table ID="tbl" runat="server">
        </asp:Table>
    <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" 
        onselectedindexchanged="DropDownList1_SelectedIndexChanged">
        <asp:ListItem>Select...</asp:ListItem>
        <asp:ListItem>Generate</asp:ListItem>
    </asp:DropDownList>
        <asp:Button ID="btnSet" runat="server" Text="Button" onclick="btnSet_Click" /> </div>
    </form>

To create dynamic control:

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (DropDownList1.SelectedIndex == 1)
        {
            CreateDynamicTable();
        }
    }
private void CreateDynamicTable()
    {
       
        // Fetch the number of Rows and Columns for the table 
        // using the properties
        int tblRows = 5;
        int tblCols = 5;
        // Now iterate through the table and add your controls 
        for (int i = 0; i < tblRows; i++)
        {
            TableRow tr = new TableRow();
            for (int j = 0; j < tblCols; j++)
            {
                TableCell tc = new TableCell();
                TextBox txtBox = new TextBox();
                txtBox.ID = "txt-" + i.ToString() + "-" + j.ToString();  
                txtBox.Text = "RowNo:" + i + " " + "ColumnNo:" + " " + j;
                // Add the control to the TableCell
                tc.Controls.Add(txtBox);
                // Add the TableCell to the TableRow
                tr.Cells.Add(tc);
               
            }
            // Add the TableRow to the Table
            tbl.Rows.Add(tr);
            tbl.EnableViewState = true;
            ViewState["tbl"] = true;
        }      
    }

On Button click:

protected void btnSet_Click(object sender, EventArgs e)
    {
        foreach (TableRow tr in tbl.Controls )
        {
            foreach (TableCell tc in tr.Controls)
            {

                if (tc.Controls[0] is TextBox)
                { 
                    Response.Write(((TextBox)tc.Controls[0]).Text);         
                }
            }
            Response.Write("<br/>");  
        }
              
    }

Right Now, No output because dynamic controls are lost in postback then what to do.
So we need to save dynamic controls value and generate dynamic controls again.we need to maintain viewstate.

protected override object SaveViewState()
    {
        object[] newViewState = new object[2];

        List<string> txtValues = new List<string>();
                
        foreach (TableRow row in tbl.Controls)
        {
            foreach (TableCell cell in row.Controls)
            {
                if (cell.Controls[0] is TextBox)
                {
                    txtValues.Add(((TextBox)cell.Controls[0]).Text);
                }
            }
        }

        newViewState[0] = txtValues.ToArray(); 
        newViewState[1] = base.SaveViewState();
        return newViewState;
    }
protected override void LoadViewState(object savedState)
    {
        //if we can identify the custom view state as defined in the override for SaveViewState
        if (savedState is object[] && ((object[])savedState).Length == 2 && ((object[])savedState)[0] is string[] )
        {
           object[] newViewState = (object[])savedState;
            string[] txtValues = (string[])(newViewState[0]);
            if (txtValues.Length > 0)
            { 
                //re-load tables
                CreateDynamicTable();
                int i = 0;
                foreach (TableRow row in tbl.Controls)
                {
                    foreach (TableCell cell in row.Controls)
                    {
                        if (cell.Controls[0] is TextBox && i < txtValues.Length)
                        {
                            ((TextBox)cell.Controls[0]).Text = txtValues[i++].ToString();

                        }
                    }
                }
            }
            //load the ViewState normally
            base.LoadViewState(newViewState[1]);
        }
        else
        {
            base.LoadViewState(savedState);
        }
    }

Hurray.. Now you can access dynamic control value on button click.

Enjoy this.