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ConfigurationManager.AppSettings Property

Gets the AppSettingsSection data for the current application's default configuration.

Namespace:  System.Configuration
Assembly:  System.Configuration (in System.Configuration.dll)

'Declaration
Public Shared ReadOnly Property AppSettings As NameValueCollection

Property Value

Type: System.Collections.Specialized.NameValueCollection
Returns a NameValueCollection object that contains the contents of the AppSettingsSection object for the current application's default configuration.

ExceptionCondition
ConfigurationErrorsException

Could not retrieve a NameValueCollection object with the application settings data.

A AppSettingsSection object contains the contents of the configuration file's appSettings section.

The first example shows a simple console application that reads application settings, adds a new setting, and updates an existing setting.

Imports System.Configuration
Module Module1

    Sub Main()
        ReadAllSettings()
        ReadSetting("Setting1")
        ReadSetting("NotValid")
        AddUpdateAppSettings("NewSetting", "May 7, 2014")
        AddUpdateAppSettings("Setting1", "May 8, 2014")
        ReadAllSettings()
    End Sub

    Sub ReadAllSettings()
        Try
            Dim appSettings = ConfigurationManager.AppSettings

            If appSettings.Count = 0 Then
                Console.WriteLine("AppSettings is empty.")
            Else
                For Each key As String In appSettings.AllKeys
                    Console.WriteLine("Key: {0} Value: {1}", key, appSettings(key))
                Next
            End If
        Catch e As ConfigurationErrorsException
            Console.WriteLine("Error reading app settings")
        End Try
    End Sub

    Sub ReadSetting(key As String)
        Try
            Dim appSettings = ConfigurationManager.AppSettings
            Dim result As String = appSettings(key)
            If IsNothing(result) Then
                result = "Not found"
            End If
            Console.WriteLine(result)
        Catch e As ConfigurationErrorsException
            Console.WriteLine("Error reading app settings")
        End Try
    End Sub

    Sub AddUpdateAppSettings(key As String, value As String)
        Try
            Dim configFile = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)
            Dim settings = configFile.AppSettings.Settings
            If IsNothing(settings(key)) Then
                settings.Add(key, value)
            Else
                settings(key).Value = value
            End If
            configFile.Save(ConfigurationSaveMode.Modified)
            ConfigurationManager.RefreshSection(configFile.AppSettings.SectionInformation.Name)
        Catch e As ConfigurationErrorsException
            Console.WriteLine("Error writing app settings")
        End Try
    End Sub

End Module

The previous example assumes your project has an App.config file as shown below.

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
  <appSettings>
    <add key="Setting1" value="May 5, 2014"/>
    <add key="Setting2" value="May 6, 2014"/>
  </appSettings>
</configuration>

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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