UserControl外的页面中的控件未在PreRender上更新

Question

Here is my code:

<asp:Label ID="myLabel" runat="server" Text="first label"></asp:Label>

<uc:myControl ID="myControl" runat="server" /> //contains a checkbox

---

myControl.ascx.cs

 public bool changeLabel { get; set; }

 protected void checkbox_CheckedChanged(object sender, EventArgs e) {
  changeLabel = ((CheckBox) sender).Checked ? true : false;
 }

---

myPage.aspx.cs

    protected void Page_PreRender(object sender, EventArgs e)
    {
        if (Page.IsPostBack)
        {
            myLabel.Text = myControl.changeLabel == true ? "second label" : "first label";
        }
    }

---

In debug mode, i can see my new value "second label" but it's not rendering in the page. Any advice ?

Answer 1

You can't set the value on post-back in pre-render, because after this event the page applies the ViewState to the control, changing its value. So you are setting it too early. A better idea would be the Page Load event.

protected void Page_Load(object sender, EventArgs e)
    {
        if (Page.IsPostBack)
        {
            myLabel.Text = myControl.changeLabel == true ? "second label" : "first label";
        }
    }

Answer 2

Try doing soemthing like this :

protected void checkbox_CheckedChanged(object sender, EventArgs e)
{
      Label l = (Label)this.Page.FindControl("myLabel");
      if (l != null && checkbox is checked)
      {
          l.Text = "second label";
      }
      else
     {
          l.Text = "first label";
     }
 }

:)