How to use a App.config file in WPF applications?

You have to reference the System.Configuration assembly which is in GAC.

Use of ConfigurationManager is not WPF-specific: it is the privileged way to access configuration information for any type of application.

Please see Microsoft Docs - ConfigurationManager Class for further info.

In my case, I followed the steps below.

App.config

<configuration>     <startup>        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />  </startup> <appSettings>   <add key="POCPublishSubscribeQueueName" value="FormatName:Direct=OS:localhost\Private$\POCPublishSubscribe"/> </appSettings></configuration>

Added System.Configuartion to my project.

Added using System.Configuration statement in file at top.

Then used this statement:

string queuePath = ConfigurationManager.AppSettings["POCPublishSubscribeQueueName"].ToString();

In your app.config, change your appsetting to:

<applicationSettings>    <WpfApplication1.Properties.Settings>        <setting name="appsetting" serializeAs="String">            <value>c:\testdata.xml</value>        </setting>    </WpfApplication1.Properties.Settings></applicationSettings>

Then, in the code-behind:

string xmlDataDirectory = WpfApplication1.Properties.Settings.Default.appsetting.ToString()