How to create dynamic number of TextBox controls using loop?

Question

I'm trying to create TextBox dynamically. But it's not working. It gives me an error:

Control '0' of type 'TextBox' must be placed inside a form tag with runat=server.

Here is my aspx code:

<asp:Content ID="Content2" ContentPlaceHolderID="body" Runat="Server">
  <form id="form" runat="server">
    <asp:Button ID="Button2" runat="server" OnClick="show" Text="Button" />
    <asp:TextBox ID="TextBox" runat="server"></asp:TextBox>
  </form>
</asp:Content>

Here is my Codebehind:

public void show(object sender, EventArgs e)
{
    for (int i =0; i <3; i++)
    {
        TextBox _text = new TextBox();
        _text.Visible = true;
        _text.Text = i.ToString();
        _text.ID = i.ToString();
        this.Controls.Add(_text);
    }
}

What is this in this context? Probably a Page right? And if the form with the runat="server" attribute is within the Page, then it stands to reason you're not adding your controls to a form with the runat="server" attribute, you're adding them to its parent. — mason
– mason, Commented Jun 17, 2016 at 13:08

Win · Accepted Answer · 2016-06-17 13:15:52Z

Even if you place controls inside form control, you won't be able to retrieve the value on postback.

The problem with dynamic control is you will need to reload the control (with same id) on every post back of the page.

Otherwise, they'll not be in the control tree, and you won't be able to find them.

Here is a sample. It loads TextBox control dynamically, and displays the value back when Submit button is clicked.

ASPX

<asp:PlaceHolder runat="server" ID="PlaceHolder1" />
<asp:Button runat="server" ID="OkButton" OnClick="OkButton_Click" Text="Ok" />
<asp:Button runat="server" ID="SubmitButton" OnClick="SubmitButton_Click" Text="Submit" />
<asp:Label runat="server" ID="MessageLabel" />

Code Behind

protected void Page_Init(object sender, EventArgs e)
{
    if (IsPostBack)
    {
        LoadControls();
    }
}

protected void OkButton_Click(object sender, EventArgs e)
{
    LoadControls();
}

protected void SubmitButton_Click(object sender, EventArgs e)
{
    var myTextBox = FindControlRecursive(PlaceHolder1, "MyTextBox") as TextBox;
    MessageLabel.Text = myTextBox.Text;
}

private void LoadControls()
{
    // Ensure that the control hasn't been added yet. 
    if (FindControlRecursive(PlaceHolder1, "MyTextBox") == null)
    {
        var myTextBox = new TextBox {ID = "MyTextBox"};
        PlaceHolder1.Controls.Add(myTextBox);
    }
}

public static Control FindControlRecursive(Control root, string id)
{
    if (root.ID == id)
        return root;

    return root.Controls.Cast<Control>()
        .Select(c => FindControlRecursive(c, id))
        .FirstOrDefault(c => c != null);
}

mason · Accepted Answer · 2016-06-17 13:11:54Z

1

Try this:

this.Form.Controls.Add(_text);

The error tells you that TextBox must be inside <form> tag. If you add it to Controls of "this", it's added after <form>.

edited Jun 17, 2016 at 13:11

mason

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answered Jun 17, 2016 at 13:11

Mario

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1 Comment

Hameed Over a year ago

Very simple and just half line answer.It's working Now.

mason · Accepted Answer · 2016-06-17 13:12:17Z

0

Add controls to the form instead of adding them to this

for (int i =0; i <3; i++)
{
    TextBox _text = new TextBox();
    _text.Visible = true;
    _text.Text = i.ToString();
    _text.ID = i.ToString();
    form.Controls.Add(_text);
}

edited Jun 17, 2016 at 13:12

mason

32.8k12 gold badges83 silver badges127 bronze badges

answered Jun 17, 2016 at 13:11

Mairaj Ahmad

14.6k2 gold badges29 silver badges43 bronze badges

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