Question

I’m using this code

<asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder>
<asp:Button ID="addnewtext" runat="server" Text="Add" onclick="addnewtext_Click" width="76px" />

and aspx.cs page code:

TextBox tb;
static int i = 0;
protected void addnewtext_Click(object sender, EventArgs e)
{
    tb = new TextBox();
    tb.ID = i.ToString();

    PlaceHolder1.Controls.Add(tb);
    i++;
}

On every click on the button I want to add another text box.

Answer 1

Reason:
When you click button again than it do postback to serverside and it removes previously added dynamically textbox

Solution:
To add it again you need to do like this

 TextBox tb;
static int i = 0;
protected void addnewtext_Click(object sender, EventArgs e)
{
        i++;
    for(j=0;j<=i;j++)
    {
    tb = new TextBox();
    tb.ID = j.ToString();

    PlaceHolder1.Controls.Add(tb);
    }

}

that means you need to create the added textbox again…because you are adding control dynamically to the page…

Article like this might help you : Retaining State for Dynamically Created Controls in ASP.NET applications