ASP.NET把动态控件页上的反向搅乱事件

Question

I have this weird problem when putting textboxes on the page in reverse. The whole event system is messed up. Changing one textbox fires TextChange on all textboxes. I can fix this by putting the controls in a list first and then call add while iterating trough the list in reverse. But i just want to know why this fails. Heres some code (.net 2.0)

public partial class _Default : Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        InitFields();
    }

    private void InitFields()
    {
        int nrFields;
        //We have a static textbox called nrElements, this determines the number
        //of fields to initialize
        if (int.TryParse(nrElements.Text, out nrFields))
        {
            //Put all the dynamic fields on the screen in reverse order
            foreach(Control t in GetDynamicFields(nrFields))
            {
                //Calling Controls.Add works fine
                //Calling Controls.AddAt messes up the events
                //Try changing different textboxes
                plhFields.Controls.AddAt(0, t);
            }
        }
    }

    private IEnumerable<Control> GetDynamicFields(int nrFields)
    {
        for (int i = 0; i < nrFields; i++)
        {
            TextBox txtBox = new TextBox();
            txtBox.ID = string.Format("dynTextBox{0}", i.ToString());
            txtBox.AutoPostBack = true;
            txtBox.TextChanged += t_TextChanged;
            yield return txtBox;
        }
    }

    private void t_TextChanged(object sender, EventArgs e)
    {
        TextBox txtBox = sender as TextBox;
        if (txtBox != null)
            txtBox.Text = txtBox.Text + "Changed ";
    }
}

Answer 1

Try calling InitFields() on the Page_PreInit event rather than Page_Load.

Or an alternative would be to override the CreateChildControls() method ( MSDN Article ), if you use CreateChildControls() you'll need to call EnsureChildControls() on the Page_Load method to make sure the CreateChildControls() method has been called before you try to access any controls which have been created within that method.

Answer 2

Always put dynamic controls in OnInit event. Then viewstate serializer/deserializer will work. And you have to add controls on every request, not just in !IsPostBack.