how can I get html attribute from ASP/vb.net Codebehind

Question

I changed from asp:tabcontainer to bootstrap nav-tabs

<div id="Tabs2" runat="server" role="tabpanel">
                <ul class="nav nav-tabs" role="tablist">
                    <li class="active"><a href="#card" aria-controls="card" role="tab" data-toggle="tab" tabindex="0">Card</a></li>
                    <li><a href="#term" aria-controls="term" role="tab" data-toggle="tab" tabindex="1">Term</a></li>
                    <li><a href="#account" aria-controls="account" role="tab" data-toggle="tab" tabindex="2">Account</a></li>
                    <li><a href="#counter" aria-controls="counter" role="tab" data-toggle="tab" tabindex="3">Counter</a></li>
                    <li><a href="#allsust" aria-controls="allsust" role="tab" data-toggle="tab" tabindex="4">All Suspect</a></li>

                </ul>
            </div

then i just need to get tabindex from html to check condition this is code from my asp:tabcontainer

Protected Sub imgPrev_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles imgPrev.Click
    GridView1.PageIndex = 0
    TextDate.Text = Func.Date2YYMMDD(DateAdd(DateInterval.Day, -1, BizFunc.YYMMDD2Date(TextDate.Text)))
    Select Case TabContainer1.ActiveTabIndex
        Case 0 : btnSearchCard_Click(sender, e)
        Case 1 : btnSearchTerm_Click(sender, e)
        Case 2 : btnSearchAccount_Click(sender, e)
        Case 3 : btnSearchCounter_Click(sender, e)
        Case 4 : btnSearchSuspect_Click(sender, e)
    End Select
End Sub

i tried to use Tabs2.attribute but i don't know what next i should do

what u are doing in these click events? if these are buttons in the tabs, it can have click events with itself? — Veena
– Veena, Commented Mar 9, 2015 at 4:54
@Veena i added more information why i use this click event i use this because of click previous button on Calendarextender — Touchy Vivace
– Touchy Vivace, Commented Mar 9, 2015 at 4:57
i think u can use a hidden field outside the tab, to store the tabindex, which is to be set when each tab is clicked(selected) — Veena
– Veena, Commented Mar 9, 2015 at 5:04

Ross Brasseaux · Accepted Answer · 2015-03-09 05:54:18Z

You cannot access the link tag <a> from the server in ASP.NET unless it has the runat="server" attribute. Here are your options:

1. Use the `<ASP:Hyperlink>` tag instead of the `<a>` tag.

If you don't mind letting ASP render the tags for you, just use their native hyperlink control.

PROS: You can access and manipulate the element from server and client side using a combination of CssClass and javascript, CSS, etc.

CONS: The tags would indeed be rendered by the server, so if you have a front-end engineer working with you, he might be at a disadvantage if he wanted to modify the layout.

2. Use Veena's solution and store the attribute value in a HiddenField

Create a <ASP:HiddenField> inside each of the list items that have a value equal to the tabindex of the corresponding <a> attribute.

PROS: You can use javascript to set the value of a HiddenField, so if you're building the field dynamically, it would work out. Also, no server-side element rendering is necessary like in option #1. This actually might be the most elegant solution if you are decent with javascript.

CONS: The actual tab-index attribute accessed by the server would be decoupled from its corresponding <a> tag. This will at best be an additional caveat to remember when working on that page, and at worst will cause unexpected behavior, exceptions, build-errors (probably not), etc. later on.

3. Add a `runat="server"` attribute to the link elements.

This would allow the server to see and access the element (albeit you may have to use one or two DirectCast functions). I'll include some code at the end of this answer that shows a method without conversion functions.

PROS: Simple. Will likely accomplish what you're trying to do in this specific case.

CONS: Some caveats exist when wrapping server controls inside HtmlGenericControls, so you'll have to keep this in mind if you decide to do more with the front-end code. To avoid this, you'll probably have to change your <div> wrapper into a <asp:PlaceHolder> tag--which I believe gets rendered as a div anyway.

If you want to go with option #3, here is a demonstration of how you would do it:

HTML

<asp:PlaceHolder runat="server" ID="test_PH">
            <ul id="test_UL">
                <li><a id="link1_undetectable" href="#" tabindex="0">Tab 0 - This will not be detected.</a></li>
                <li><a id="link2_undetectable" href="#" tabindex="1">Tab 1 - This will not be detected.</a></li>
                <li><a id="link3_undetectable" href="#" tabindex="2">Tab 2 - This will not be detected.</a></li>
                <li><a id="link4_undetectable" href="#" tabindex="3">Tab 3 - This will not be detected.</a></li>
                <li><a id="link5_undetectable" href="#" tabindex="4">Tab 4 - This will not be detected.</a></li>
                <li><a id="link6" href="#" runat="server" tabindex="5">Tab 5</a></li>
                <li><a id="link7" href="#" runat="server" tabindex="6">Tab 6</a></li>
                <li><a id="link8" href="#" runat="server" tabindex="7">Tab 7</a></li>
                <li><a id="link9" href="#" runat="server" tabindex="8">Tab 8</a></li>
                <li><a id="link10" href="#" runat="server" tabindex="9">Tab 9</a></li>
            </ul>
        </asp:PlaceHolder>

VB.NET

    Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
        Dim ph As PlaceHolder = test_PH, sb As New StringBuilder() ' The string builder is just for demonstration purposes.

        For Each c As HtmlAnchor In ph.Controls.OfType(Of HtmlAnchor)() ' This will loop through the HtmlAnchors without throwing an exception.
            sb.AppendLine(String.Format("ID: ""{0}""; Tab-index: ""{1}""", c.ID, c.Attributes("tabindex"))) ' This builds a string for demo purposes.
        Next

        MsgBox(sb.ToString) 'Show the string for demo purposes.
    End Sub

Result...

Results

Tim · Accepted Answer · 2015-03-09 05:12:17Z

0

Only server side controls can be directly accessed within asp code. So you have a few options.

Add runat="server"' attributes in your markup to make the controls into server-side controls.
Use JavaScript to save off the attribute value into a hidden form field that can be submitted when you button is clicked.

answered Mar 9, 2015 at 5:12

Tim

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how can I get html attribute from ASP/vb.net Codebehind

2 Answers 2

1. Use the `<ASP:Hyperlink>` tag instead of the `<a>` tag.

2. Use Veena's solution and store the attribute value in a HiddenField

3. Add a `runat="server"` attribute to the link elements.

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2 Answers 2

1. Use the <ASP:Hyperlink> tag instead of the <a> tag.

2. Use Veena's solution and store the attribute value in a HiddenField

3. Add a runat="server" attribute to the link elements.

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1. Use the `<ASP:Hyperlink>` tag instead of the `<a>` tag.

3. Add a `runat="server"` attribute to the link elements.