The configurationmanager class cannot be found in the system. Configuration namespace.

Here we talk about the problem of calling layer-3 programming in class:

Start to use VS 2005 and habitually use the configurationsettings class to read applications.ProgramThe compiler prompts the following information:
Warning 1 "system. configuration. configurationsettings. receivettings" is out of date: "This method is obsolete,
It has been replaced by system. Configuration! System. configuration. configurationmanager. deleetmanager"

So I tried to find the configurationmanager class to use. The result is that the configurationmanager class cannot be found in the system. Configuration namespace,
However, you can turn to the network to know that you still need to add references to the system. configuration. dll file ~~

After the event, I noticed that the original MS prompts a bit about this, but it is just a bit obscure --
This method is obsolete, it has been replaced by system. Configuration! System. configuration. configurationmanager. deleetmanager

I noticed no. The above section has more system. Configuration! This section ~
For example:
String we = system. configuration. configurationmanager. receivettings ["SQL"];

For example:
System. Web. httpcontext. Current. cache ["cache1"] = "value1 ";
System. Web. dll