Why is <clear></clear> not the same as <clear /> in app.config?

Question

Can someone please give me the technical reason why <clear></clear> is invalid in app.config vs <clear />

It's typically used like this :

<connectionStrings>
 <clear/>
 <add etc..... />
</connectionStrings>

Problem is I'm using an installer product (InstallShield) with does xml transformation to app.config files, and it's changing <clear /> to <clear></clear>

This breaks the application (service won't even start)

For now I'm just looking for the technical explanation, but if you have any workaround that would be nice too.

Answer 1

It seems that using <clear></clear> breaks the parsing of the connectionStrings section (and probably others too, if used there). See the comment of Hans Passant for a possible explanation.

If <clear></clear> is present, the ConfigurationManager.ConnectionStrings is empty. So the reason for you service crashing may be, that you don't check if this collection contains any elements or try to access them via ConfigurationManager.ConnectionStrings["nameoftheconnection"] which throws an exception if there is no element with that key.

Possible workarounds (which I admin are both rather clumsy and hacky)

1. You remove the <clear />. This may lead to some additional connect strings created by some referenced assemblies. But as your own connectionstring should be at the end of this collection, you may be able to remove the unwanted entries.

2. You add a custom task to your installation routine, which processes the app.config file in one of the later steps and replaces <clear></clear> with <clear />