How to use ConfigurationManager

Question

I want to use App.config for storing some setting. I tried to use the next code for getting a parameter from a config file.

private string GetSettingValue(string paramName)
{
    return String.Format(ConfigurationManager.AppSettings[paramName]);
}

I also added System.Configuration for it (I used a separate class), and in App.config file I have:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <startup> 
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
  </startup>
  <appSettings>
    <add key ="key1" value ="Sample" />
  </appSettings>
</configuration>

But I got an error while trying to use ConfigurationManager - ConfigurationManager can't exist in such context, but I already added System.Configuration. Or did I miss something?

EDIT:

class with config (full view)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Configuration;

namespace browser
{
    class ConfigFile
    {
        private string GetSettingValue(string paramName)
        {
            return String.Format(ConfigurationManager.AppSettings[paramName]);
        }
    }
}

EDIT2

Add how it looks

This means the problem is not during using ConfigurationManger but before - the program "says" that it "doesn't know such element" as I understand the error - the "Element ConfigurationManager" doesn't exist in such context"

EDIT3

EDIT 4

Answer 1

I found some answers, but I don't know if it is the right way.This is my solution for now. Fortunatelly it didn´t broke my design mode.

    `
    /// <summary>
    /// set config, if key is not in file, create
    /// </summary>
    /// <param name="key">Nome do parâmetro</param>
    /// <param name="value">Valor do parâmetro</param>
    public static void SetConfig(string key, string value)
    {
        var configFile = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
        var settings = configFile.AppSettings.Settings;
        if (settings[key] == null)
        {
            settings.Add(key, value);
        }
        else
        {
            settings[key].Value = value;
        }
        configFile.Save(ConfigurationSaveMode.Modified);
        ConfigurationManager.RefreshSection(configFile.AppSettings.SectionInformation.Name);
    }

    /// <summary>
    /// Get key value, if not found, return null
    /// </summary>
    /// <param name="key"></param>
    /// <returns>null if key is not found, else string with value</returns>
    public static string GetConfig(string key)
    {
        return ConfigurationManager.AppSettings[key];
    }`

Answer 2

Okay, it took me a while to see this, but there's no way this compiles:

return String.(ConfigurationManager.AppSettings[paramName]);

You're not even calling a method on the String type. Just do this:

return ConfigurationManager.AppSettings[paramName];

The AppSettings KeyValuePair already returns a string. If the name doesn't exist, it will return null.

---

Based on your edit you have not yet added a Reference to the System.Configuration assembly for the project you're working in.