How to check key values in appsettings

have a look at the below links also .

ConfigurationManager Class (System.Configuration)[^]

ConfigurationManager.AppSettings Property (System.Configuration)[^]

Please try below .

string  option = "123"; // read from text box
          string KeyName = "KeyList"; // key name as in app.config file

           if (ConfigurationManager.AppSettings.AllKeys.Contains(KeyName))
           {
               //key exist
               String KeyValue = ConfigurationManager.AppSettings[KeyName].ToString();
               if (KeyValue.Trim().Contains(option))
               {
                   //Key value found
                   //MessageBox.Show(name);

               }
           }

So I've provided 2 ways of finding out what you want. Looking through any key in appsettings regardless of the key name, and then finding the specific value of the key by keyname.

My appsettings:

<appSettings>
    <add key="KeyList" value="123,234,345,456"/>
    <add key="AnotherSetting" value="123,234,345,456"/>
  </appSettings>

Searching through all keys to find any key with a value of 123

var allkeys = ConfigurationManager.AppSettings.AllKeys;

            foreach (var key in allkeys)
            {
                var value = ConfigurationManager.AppSettings[key];

                if (value.Contains("123"))
                {
                    Console.WriteLine("My app setting has a value of 123 on key {0}", key);
                }
            }

Picking the key by a specified name and checking the value.

var specificKey = ConfigurationManager.AppSettings["KeyList"];

            if (!string.IsNullOrEmpty(specificKey) && specificKey.Contains("123"))
            {
                Console.WriteLine("KeyList contains 123");
            }

Then if you are sure that all keys in your appsettings will be a CSV. You can do something like this to find any key that contains 123 (not 123456).

var csvKey = ConfigurationManager.AppSettings.AllKeys;

            foreach (var key in csvKey)
            {
                var values = ConfigurationManager.AppSettings[key].Split(',');

                foreach (var item in values)
                {
                    if (item == "123")
                    {
                        Console.WriteLine("My app setting has a value of 123 on key {0}", key);    
                    }
                }
            }