Dynamic Control’s Event Handler’s Working

Question

I have following code that adds dynamic LinkButton on the click event of a normal button. The LinkButtons need a EventHandler “LinkButton_Click“. Since the event handler need to be registered while Page_Load/Page_Init itself, I am first adding all the possible links within Page_Load (in postback scenario). (There are totally fours linkbuttons; only two will be displayed in the screen based on business scenario)

The code is working fine and the event handlers are getting invoked on click event.

Note: The business scenario is – if the current time’s second portion is less than 30, the first two LinkButtons need to be displayed; if greater than 30 the last two LinkButtons need to be displayed.

Note: The controls are cleared and added again inside PopulateLinksBasedOnCriteria() method

QUESTIONS

1. In the PopulateLinksBasedOnCriteria() method, I am newly creating the link button instances. Still the event handler is firing. This is working because the ID that got added in the Page_Load is same. Is there any MSDN reference that substantiate this behavior? (I.e. the event handler will be based on the IDs registered while Page_Load/Page_Init. This will work even if the controls are cleared and added again)
2. There is duplicate code in creating LinkButtons – one inside Page_Load and other inside PopulateLinksBasedOnCriteria() method. Is there a better way to achieve this business task without duplicate code?

MarkUp

<form id="form1" runat="server">
<div>
    <asp:Button ID="btnAdd" runat="server" Text="Add" OnClick="btnAdd_Click" />
    <br />
    <asp:PlaceHolder ID="plhDynamicLinks" runat="server"></asp:PlaceHolder>
</div>
</form>

CODE BEHIND

    protected void Page_Load(object sender, EventArgs e)
    {

        if (Page.IsPostBack)
        {
            LinkButton lnk1 = new LinkButton();
            lnk1.ID = "D1";
            lnk1.Text = "A";
            //Event handler must be registered in the Page_Load/Page_Init
            lnk1.Click += new EventHandler(LinkButton_Click);
            plhDynamicLinks.Controls.Add(lnk1);

            LinkButton lnk2 = new LinkButton();
            lnk2.ID = "D2";
            lnk2.Text = "B";
            lnk2.Click += new EventHandler(LinkButton_Click);
            plhDynamicLinks.Controls.Add(lnk2);

            LinkButton lnk3 = new LinkButton();
            lnk3.ID = "D3";
            lnk3.Text = "C";
            lnk3.Click += new EventHandler(LinkButton_Click);
            plhDynamicLinks.Controls.Add(lnk3);

            LinkButton lnk4 = new LinkButton();
            lnk4.ID = "D4";
            lnk4.Text = "D";
            lnk4.Click += new EventHandler(LinkButton_Click);
            plhDynamicLinks.Controls.Add(lnk4);

        }
    }

    protected void LinkButton_Click(object sender, EventArgs e)
    {
        PopulateLinksBasedOnCriteria();
        LinkButton clickedControl = (LinkButton)sender;
        Response.Write(DateTime.Now.ToString()+"___"+ clickedControl.ID + " Link Button Clicked" );
    }

    protected void btnAdd_Click(object sender, EventArgs e)
    {
        PopulateLinksBasedOnCriteria();
    }

    private void PopulateLinksBasedOnCriteria()
    {
        plhDynamicLinks.Controls.Clear();

        if (DateTime.Now.Second < 30)
        {
            LinkButton linkButton1 = new LinkButton();
            linkButton1.ID = "D1";
            linkButton1.Text = "1";
            plhDynamicLinks.Controls.Add(linkButton1);

            LinkButton linkButton2 = new LinkButton();
            linkButton2.ID = "D2";
            linkButton2.Text = "2";
            plhDynamicLinks.Controls.Add(linkButton2);
        }
        else
        {
            LinkButton linkButton3 = new LinkButton();
            linkButton3.ID = "D3";
            linkButton3.Text = "3";
            plhDynamicLinks.Controls.Add(linkButton3);

            LinkButton linkButton4 = new LinkButton();
            linkButton4.ID = "D4";
            linkButton4.Text = "4";
            plhDynamicLinks.Controls.Add(linkButton4);
        }
    }

Answer 1

I would suggest detecting what causes the PostBack in Page_Load Event On postback, how can I check which control cause postback in Page_Init event and then

 if (Page.IsPostBack && *PostBackControl.Name=="btnAdd"*)
            {
if (DateTime.Now.Second < 30)
        {
                LinkButton lnk1 = new LinkButton();
                lnk1.ID = "D1";
                lnk1.Text = "A";
                //Event handler must be registered in the Page_Load/Page_Init
                lnk1.Click += new EventHandler(LinkButton_Click);
                plhDynamicLinks.Controls.Add(lnk1);

                LinkButton lnk2 = new LinkButton();
                lnk2.ID = "D2";
                lnk2.Text = "B";
                lnk2.Click += new EventHandler(LinkButton_Click);
                plhDynamicLinks.Controls.Add(lnk2);
    } else
        {
                LinkButton lnk3 = new LinkButton();
                lnk3.ID = "D3";
                lnk3.Text = "C";
                lnk3.Click += new EventHandler(LinkButton_Click);
                plhDynamicLinks.Controls.Add(lnk3);

                LinkButton lnk4 = new LinkButton();
                lnk4.ID = "D4";
                lnk4.Text = "D";
                lnk4.Click += new EventHandler(LinkButton_Click);
                plhDynamicLinks.Controls.Add(lnk4);
    }
            }
        }