Re: JavaScript Statement Question
- From: "Richard Thomas" <rthomas@xxxxxxxxxxx>
- To: <programmingblind@xxxxxxxxxxxxx>
- Date: Sun, 21 Oct 2007 12:25:23 -0400
Hi Jim:
Here is the actual article I'm evaluating. I get everything except that bloody
{0}
It's not very long and you can just blast to where I labeled RtHere if you
want to see it used in context.
Here is the original article:
devised the followingsolution.
First, the TreeView knows which node is selected because
SelectedNode
is a property of the TreeView control. This information has to be stored
somewhere,
nd what is selected ultimately is rendered as HTML. If I know the ID of the
selected
HTML control, then I should be able to scroll and focus it. Sure enough, if you
look
at the source HTML of a page with a TreeView on it, you will find the
declaration
of a hidden <INPUT> tag-think text box-whose ID is approximately
RtHere, this is what the GetElementId will point to to get the value.
TreeViewx_SelectedNode:
<input type="hidden" name="TreeView1_SelectedNode" id="TreeView1_SelectedNode"
value="TreeView1t54" />
With this knowledge, the idea is that a hidden input control is basically a
textbox
and all you need to do is figure out what the contents are. A TreeView is
rendered
as an HTML table-that's all ASP.NET controls are, little HTML code
generators-and
the value field is the client identifier of a table cell, a <TD> tag
representing
the node. So find the ID of the cell tag, scroll it into view, and you are done.
[Note to ASP.NET team: This should be a property of the TreeView. Thank you.]
To demonstrate, I wrote some code to generate a really full TreeView. The
Page_Load
event injects some JavaScript to find and focus the table cell (see Listing 1)
and
the <body> tag's
onload event calls this injected function.
Listing 1: The Code Behind That Fills a Treeview and Injects the JavaScript
Imports System.Collections.Generic
Partial Class _Default
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles Me.Load
InjectLoadEvent()
If (IsPostBack) Then Return
TreeView1.Nodes.Clear()
Dim chicken As New TreeNode("Chicken")
TreeView1.Nodes.Add(chicken)
Dim beef As New TreeNode("Beef")
TreeView1.Nodes.Add(beef)
RtHere, I removed the rest of the demo nodes.
TreeView1.CollapseAll()
End Sub
Public Sub InjectLoadEvent()
Dim script As String = _
"function LoadEvent()" + _
{" + _
" try" + _
" {{" + _
RtHere: here is the actual statement.
The rendered Html is below.
" var elem = document.getElementById('{0}_SelectedNode');" + _" if(elem !=
null )" + _
" {{" + _
" var node = document.getElementById(elem.value);" + _
" if(node != null)" + _
" {{" + _
" node.scrollIntoView(true);" + _
" {1}.scrollLeft = 0;" + _
" }}" + _
" }}" + _
" }}" + _
" catch(oException)" + _
" {{}}" + _
"}}"
Page.ClientScript.RegisterClientScriptBlock(Me.GetType(), "LoadEvent", _
String.Format(script, TreeView1.ClientID, Panel1.ClientID), True)
End Sub
End Class
Listing 2 shows the complete page.
Listing 2: The ASP Code That Defines the Appearance of this Relatively Simple
Page
<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb"
Inherits="_Default"
%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd";>
<html xmlns="http://www.w3.org/1999/xhtml"; >
<head runat="server">
<title>Focus Tree Node on Postback</title>
</head>
<body onload="LoadEvent()">
<form id="form1" runat="server">
<div>
<asp:Panel ID="Panel1" runat="server" Height="200px" Width="200px"
ScrollBars="Both">
<asp:TreeView ID="TreeView1" runat="server">
<SelectedNodeStyle BackColor="#8080FF" />
</asp:TreeView>
</asp:Panel>
</div>
</form>
</body>
</html>
Figure 1 presents an example of what the simple page looks like.
Click here for a larger image.
Figure 1: A TreeView Nested in a Scrollable Panel Control (in IE7)
Finally, Listing 3 shows the resultant JavaScript, which is the interesting
part.
RtHere:, the rendered version.
Listing 3: The Injected JavaScript
<script>
function LoadEvent()
{
try
{
var elem = document.getElementById('TreeView1_SelectedNode');
if(elem != null )
{
var node = document.getElementById(elem.value);
if(node != null)
{
node.scrollIntoView(true);
Panel1.scrollLeft = 0;
}
}
}
catch(oException)
{}
}// -->
</script>
The JavaScript function
LoadEvent
finds the hidden input field. I injected all of the code expect the
ClientID
of the TreeView, which in this case is TreeView1 but in deeply nested pages can
have an ungodly long name. When I get that control, I use its value property to
find
the table cell, and with that control I invoke
scrollIntoView. The scrollLeft
f property keeps the Panel scrolled to the left. And it works!
----- Original Message -----
From: Jim
To: programmingblind@xxxxxxxxxxxxx
Sent: Sunday, October 21, 2007 10:40 AM
Subject: Re: JavaScript Statement Question
Hi Richard,
I think it should be brackets rather than braces. Brackets contain indexes to
array items.
Thanks.
Jim
__________
Take back your shopping life at http://tinyurl.com/32rsxz
----- Original Message -----
From: Richard Thomas
To: programmingblind@xxxxxxxxxxxxx
Sent: Sunday, October 21, 2007 7:55 AM
Subject: JavaScript Statement Question
Hi:
In this statement what is the '{0}'?
" var elem = document.getElementById('{0}_SelectedNode');" I know the
single parameter inside the GetElementById is the Id Tagg value of the control
to look up but the tag he looks up has an id of something like
Panel1_SelectedNode that it looks like he may be replacing with the {0} in the
GetElementById Statement.
haven't found anything, actually too much, on the statement but nothing
using '{0}'.
What is it called, index or something and what does it mean? I'll dig
around more if I can find something to google on that points to this particular
syntax.
My guess is it has to do with a Document Control relative Reference or
something but I just can't find anything like it googling so far.
Thanks:Rick Farmington Mich. USA
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