What is App.config in C#.NET? How to use it?

Question

I have done a project in C#.NET where my database file is an Excel workbook. Since the location of the connection string is hard coded in my coding, there is no problem for installing it in my system, but for other systems there is.

Is there a way to prompt the user to set a path once after the setup of the application is completed?

The answers I got was "Use App.Config"... can anyone tell what is this App.config and how to use it in my context here?

Answer 1

At its simplest, the app.config is an XML file with many predefined configuration sections available and support for custom configuration sections. A "configuration section" is a snippet of XML with a schema meant to store some type of information.

• Overview (MSDN)
• Connection String Configuration (MSDN)

Settings can be configured using built-in configuration sections such as connectionStrings or appSettings. You can add your own custom configuration sections; this is an advanced topic, but very powerful for building strongly-typed configuration files.

Web applications typically have a web.config, while Windows GUI/service applications have an app.config file.

Application-level config files inherit settings from global configuration files, e.g. the machine.config.

Reading from the App.Config

Connection strings have a predefined schema that you can use. Note that this small snippet is actually a valid app.config (or web.config) file:

<?xml version="1.0"?>
<configuration>
    <connectionStrings>   
        <add name="MyKey" 
             connectionString="Data Source=localhost;Initial Catalog=ABC;"
             providerName="System.Data.SqlClient"/>
    </connectionStrings>
</configuration>

Once you have defined your app.config, you can read it in code using the ConfigurationManager class. Don't be intimidated by the verbose MSDN examples; it's actually quite simple.

string connectionString = ConfigurationManager.ConnectionStrings["MyKey"].ConnectionString;

Writing to the App.Config

Frequently changing the *.config files is usually not a good idea, but it sounds like you only want to perform one-time setup.

See: Change connection string & reload app.config at run time which describes how to update the connectionStrings section of the *.config file at runtime.

Note that ideally you would perform such configuration changes from a simple installer.

Location of the App.Config at Runtime

Q: Suppose I manually change some <value> in app.config, save it and then close it. Now when I go to my bin folder and launch the .exe file from here, why doesn't it reflect the applied changes?