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Custom section in App.Config, ConfigurationManager stops working

I have created a console app in c# that reads information from App.config. if i add things in appSettings section, i can acces them and it works, but as soon as i add some custom sections i cant read anything from it. I am using ConfigurationManager, and i have the reference for it included.
My app config looks like this:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" />
</startup>
<appSettings>
<add key="overwriteBackupFiles" value="False"/>
<add key="path" value="c:\temp"/>
</appSettings>
<ImageFormatsINeed>
<add key="type1" value="width=180&height=180"></add>
<add key="type2" value="width=220&height=220"></add>
<add key="type3" value="width=500&height=500"></add>
</ImageFormatsINeed>
</configuration>
and i am trying to acces those information like this:
string path = ConfigurationManager.AppSettings["path"];
var settings = ConfigurationManager.GetSection("ImageFormatsINeed");
When i didnt have the ImageFormatsINeed section i could get the path from AppSettings and it was working. But as soon as i added my ImageFormatsINeed section, everything stops working.
Now my question is how can i add custom sections in app.config that it will work, or should i just read my ImageInformation from some custom xml file or config file?

You have to use the tag <configSections> at the top in your app.config, for this case you should use the type AppSettingsSection
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<configSections>
<section name="ImageFormatsINeed" type="System.Configuration.AppSettingsSection" />
</configSections>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" />
</startup>
<appSettings>
<add key="overwriteBackupFiles" value="False"/>
<add key="path" value="c:\temp"/>
</appSettings>
<ImageFormatsINeed>
<add key="type1" value="width=180&height=180"></add>
<add key="type2" value="width=220&height=220"></add>
<add key="type3" value="width=500&height=500"></add>
</ImageFormatsINeed>
</configuration>
Then in your C# code:
NameValueCollection settings_section = ConfigurationManager.GetSection("ImageFormatsINeed") as NameValueCollection;
Console.WriteLine(settings_section["type1"]);

How to retrieve the value for the Key in the Web.Config using DictionarySectionHandler

How to fetch the corresponding value of a key that I would get dynamically. I wish to use the system defined DictionarySectionHandler to do the job, of fetching the data from my custom built config section in the Web.config file
Code block in Web.Config
<section name="domainsource" type="System.Configuration.DictionarySectionHandler"/>
<domainSource>
<add key="0" value="170" />
<add key="1" value="171" />
<add key="2" value="172" />
<add key="3" value="173" />
<add key="12" value="174" />
</domainSource>
Sourcecode in the main cs file from where I wish to retrieve the data from the Web.Config
Hashtable statusCodes = ConfigurationManager.GetSection("domainSource") as Hashtable;
vDomainSource = statusCodes[vDomainID];
This is where I am stuck vDomainID would be a value 0/1/2/3/12, based on this value I need to fetch its respective Source from the Web.Config. Any help on this aspect would be really appreciated.

You have a missspelling in the defintion of the section domainsource -> domainSource. Further ensure that the elemnt is defined in an element. Then it should work.
<configuration>
<configSections>
<section name="domainSource" type="System.Configuration.DictionarySectionHandler"/>
</configSections>
<domainSource>
<add key="0" value="170" />
<add key="1" value="171" />
<add key="2" value="172" />
<add key="3" value="173" />
<add key="12" value="174" />
</domainSource>
</configuration>

How to use custom configuration file or app.config in .NET application

I have MVC5 .NET 4.6.1 C# web application
I want to create a custom config file separate from web.config to store some settings my application uses.
I tried to follow this article https://support.microsoft.com/en-us/kb/815786
however the items I set in app.config:
<?xml version="1.0"?>
<configuration>
<system.web>
<compilation debug="true" targetFramework="4.6.1" />
<httpRuntime targetFramework="4.6.1" />
</system.web>
<appSettings>
<add key="Key0" value="0" />
<add key="Key1" value="1" />
<add key="Key2" value="2" />
</appSettings>
</configuration>
are not seen in my application see , eg. they come as null:
string attr = ConfigurationManager.AppSettings["Key0"];
Why isn't it working? Am I missing something?
Alternatively I would like to create a custom config file eg. mycustom.config to define my global app settings.
EDIT
Solution I used
Follwing this post https://social.msdn.microsoft.com/Forums/vstudio/en-US/11e6d326-c32c-46b1-a9a2-1fbef96f33ee/howto-custom-configuration-files?forum=netfxbcl
In web.config:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<configSections>
<section name="newAppSettings" type="System.Configuration.AppSettingsSection, System.Configuration, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
</configSections>
<newAppSettings file="C:\mycustom.config"/>
</configuration>
Then mycustom.config
<?xml version="1.0" encoding="utf-8" ?>
<newAppSettings>
<add key="OurKey" value="OurValue"/>
</newAppSettings>
And reading the value:
System.Collections.Specialized.NameValueCollection newAppSettings = (System.Collections.Specialized.NameValueCollection)System.Configuration.ConfigurationManager.GetSection("newAppSettings");
string key = Convert.ToDateTime(newAppSettings["OurKey"]);

You can use separate config file for connection strings and app settings:
<appSettings configSource="appSettings.config" />
<connectionStrings configSource="connectionStrings.config"/>
appSettings.config file
<?xml version="1.0" encoding="utf-8" ?>
<appSettings>
<add key="Setting1" value="App setting 1" />
</appSettings>
connectionStrings.config file
<?xml version="1.0" encoding="utf-8"?>
<connectionStrings>
<add name="MyConnStr1" connectionString="My connection string" />
</connectionStrings>
Usage is same as it was before:
var setting1 = ConfigurationManager.AppSettings["Setting1"];
var connString1 = ConfigurationManager.ConnectionStrings["MyConnStr1"].ConnectionString;

//Helps to open the Root level web.config file.
Configuration webConfigApp = WebConfigurationManager.OpenWebConfiguration("~");
//Modifying the AppKey from AppValue to AppValue1
webConfigApp.AppSettings.Settings["AppKey"].Value = "AppValue1";
<appSettings>
<add key="AppKey" value="AppValue"/>
</appSettings>

How to use ConfigurationManager.AppSettings with a custom section?

I need to get "http://example.com" from using App.config file.
But at the moment I am using:
string peopleXMLPath = ConfigurationManager.AppSettings["server"];
I cannot get the value.
Could you point out what I am doing wrong?
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<configSections>
<section name="device" type="System.Configuration.SingleTagSectionHandler" />
<section name="server" type="System.Configuration.SingleTagSectionHandler" />
</configSections>
<device id="1" description="petras room" location="" mall="" />
<server url="http://example.com" />
</configuration>

I think you need to get the config section, and access that:
var section = ConfigurationManager.GetSection("server") as NameValueCollection;
var value = section["url"];
And you also need to update your config file:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<configSections>
<section name="device" type="System.Configuration.NameValueSectionHandler" />
<section name="server" type="System.Configuration.NameValueSectionHandler" />
</configSections>
<device>
<add key="id" value="1" />
<add key="description" value="petras room" />
<add key="location" value="" />
<add key="mall" value="" />
</device>
<server>
<add key="url" value="http://example.com" />
</server>
</configuration>
Edit: As CodeCaster mentioned in his answer, SingleTagSectionHandler is for internal use only. I think NameValueSectionHandler is the preferred way to define config sections.

The SingleTagSectionHandler documentation says:
This API supports the .NET Framework infrastructure and is not intended to be used directly from your code.
You can retrieve it as a HashTable and access its entries using Configuration.GetSection():
Hashtable serverTag = (Hashtable)ConfigurationManager.GetSection("server");
string serverUrl = (string)serverTag["url"];

string peopleXMLPath = ConfigurationManager.AppSettings["server"];
gets the value from the appSettings part of the app.config file but you are storing your value in
<server url="http://example.com" />
Either put the value in the appSettings section as below or retrieve the value from its current location.
You need to add a key value pair to your config's appSettings section. As below:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<appSettings>
<add key="server" value="http://example.com" />
</appSettings>
</configuration>
Your reading code is correct but you should probably check for null. If the code fails to read the config value the string variable will be null.

You're defining a configuration section instead of a value in AppSettings. You can simply add your setting to AppSettings:
<appSettings>
... may be some settings here already
<add key="server" value="http://example.com" />
</appSettings>
Custom config sections are typically used for more complicated configurations (e.g. multiple values per key, non-string values, etc.

If you want to get the value from the app settings your appsetting element in configuration file must have a key.
define your sever value as mentioned below under configuration section:
<configuration>
<appSettings>
<add key="server" value="http://example.com" />
</appSettings>
...
...
...
</configuration>
Now execute below code line to get the server url:
string peopleXMLPath = ConfigurationManager.AppSettings["server"].ToString();

Mindscape.LightSpeed Database connectivity problem

I'm using Mindspace.Lightspeed in my C# desktop application for the first time but I'm getting errors and unable to connect to database.
My App.config contains the following code:
<?xml version="1.0" encoding="utf-8" ?><configuration>
<configSections>
<section name="lightSpeedContext" type="Mindscape.LightSpeed.Configuration.LightSpeedConfigurationSection,Mindscape.LightSpeed" /></configSections><connectionStrings>
<add name="DefectsConStr" connectionString="Data Source=.\sqlexpress2k5;Initial Catalog=Defects;Persist Security Info=True;User ID=sa;Password=123"
providerName="System.Data.SqlClient" /></connectionStrings> <lightSpeedContext>
<add name="Development" connectionStringName="DefectsConStr" dataProvider="SqlServer2005"/> </lightSpeedContext> </configuration>

I have managed to reproduce your problem, you need to change your configuration file so that the section name is
lightSpeedContexts and not lightSpeedContext
see my configuration file
<?xml version="1.0"?>
<configuration>
<configSections>
<section name="lightSpeedContexts" type="Mindscape.LightSpeed.Configuration.LightSpeedConfigurationSection,Mindscape.LightSpeed"/>
</configSections>
<connectionStrings>
<add name="Blog" connectionString="Data Source=Blog.dat"/>
</connectionStrings>
<lightSpeedContexts>
<add name="Blog" connectionStringName="Blog" dataProvider="SQLite3" identityMethod="KeyTable" pluralizeTableNames="false"/>
</lightSpeedContexts>
</configuration>