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Editorial Team
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Asked: 2026-05-20T23:46:57+00:00

I have question: when I to use <%= ConfigurationManager.AppSettings[xxx] %> and <%$ AppSettings: xxx

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I have question: when I to use <%= ConfigurationManager.AppSettings["xxx"] %> and <%$ AppSettings: xxx %>.

Sometimes when I use <%= ConfigurationManager.AppSettings["xxx "] %> a I got the following error: “Server tags cannot contain <% … %> constructs”. Then a put <%$ AppSettings: xxx %> and it works.

Like this example:
Error:

<asp:Literal runat="server" ID="Literal9" Text="<%= ConfigurationManager.AppSettings["xxx"] %>"></asp:Literal>

Working:

<asp:Literal runat="server" ID="Literal9" Text='<%$ AppSettings: xxx %>'></asp:Literal>
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1 Answer

  1. Editorial Team

    The error occurs not because you’re switching between ConfigurationManager.AppSettings and AppSettings, but because of the symbol used after <%. You can’t have code rendering markup inside a server-side control that renders markup. The second way works because it evaluates the expression prior to server-side control render.

    My preference is to always use ConfigurationManager.AppSettings, because it’s more clear as to what the code is accessing.

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