Question

Recently, I had a user control I was developing throw an exception. I know what caused the exception, but this issue got me thinking. If I have a user control throw an exception for whatever reason and I wish to replace that usercontrol with something else (e.g. an error saying, "Sorry, this part of the page broke.") and perhaps log the error, what would be a good way to do it that could be done independently of what the user control is or does (i.e. I m not saying what the user control does/is, because I want an answer where that is irrelevant).

Code sample:

<asp:TableRow VerticalAlign="Top" HorizontalAlign="Left">
    <asp:TableCell>
        <UR:MyUserControl ID="MyUserControl3" runat="server" FormatString="<%$ AppSettings:RVUC %>"
            ConnectionString="<%$ ConnectionStrings:WPDBC %>" Title="CO" />
    </asp:TableCell>
    <asp:TableCell>
        <UR:MyUserControl ID="MyUserControl4" runat="server" FormatString="<%$ AppSettings:RVUA %>"
            ConnectionString="<%$ ConnectionStrings:WPDBA %>" Title="IEAO" />
    </asp:TableCell>
</asp:TableRow>

Answer 1

There s two things at work here:

Catching the error
Swapping in an "error" control

Catching the error is pretty straightfoward. It comes down to try...catch around the code that could conceivably throw an error.

As for swapping in the error control (in the catch block), there s a couple ways to do it.

You could have a hidden placeholder in your control that you just display that says, "there was an error." So, you re not removing the bad control, just replacing what it says.
Each control has a "Parent" which has a "Controls" collection (which the current control will be part of). So, you could iterate the Parent.Controls collection to find the current control, then do "Parent.AddAt(index, myErrorControl)" to insert the error control, then remove the current control (or just set "Visible = false" on it).

Answer 2

General ID: for ASP.NET it might work (not sure about ASP)

Before rendering each control - record it s id.

String CtrlID;

before each control:

CtrlID = control.name

put everything in try/catch (or do it to each control)

catch (Exception EX)
{
  hide(ctrlId)  (either set visible=false, or whatever suits you)
  show(error message)

}

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