How to check if an appSettings key exists

Question

How do I check to see if an Application Setting is available     i e  app config   lt  xml version  1 0  encoding  utf-8    gt   lt configuration gt     lt appSettings gt       lt add key   someKey  value  someValue   gt     lt  appSettings gt   lt  configuration gt    and in the codefile  if  ConfigurationManager AppSettings ContainsKey  someKey           Do Something  else       Do Something Else

User · Accepted Answer

MSDN  Configuration Manager AppSettings  if  ConfigurationManager AppSettings name     null       Now do your magic       or  string s   ConfigurationManager AppSettings  myKey    if   String IsNullOrEmpty s            Key exists   else          Key doesn t exist

User · Answer

I liked codebender s answer  but needed it to work in C   CLI   This is what I ended up with   There s no LINQ usage  but works   generic  lt typename T gt  T MyClass  ReadAppSetting String  searchKey  T defaultValue      for each  String  setting in ConfigurationManager  AppSettings- gt AllKeys        if  setting- gt Equals searchKey         if the key is in the app config       try                                see if it can be converted         auto converter   TypeDescriptor  GetConverter  Type   T  typeid             if  converter    nullptr    return  T converter- gt ConvertFromString ConfigurationManager  AppSettings searchKey              catch  Exception  ex        nothing to do             return defaultValue

User · Answer

var isAlaCarte        ConfigurationManager AppSettings AllKeys Contains  IsALaCarte    amp  amp       bool Parse ConfigurationManager AppSettings Get  IsALaCarte

User · Answer

If the key you are looking for isn t present in the config file  you won t be able to convert it to a string with  ToString   because the value will be null and you ll get an  Object reference not set to an instance of an object  error   It s best to first see if the value exists before trying to get the string representation   if   String IsNullOrEmpty ConfigurationManager AppSettings  myKey           String myKey   ConfigurationManager AppSettings  myKey   ToString        Or  as Code Monkey suggested   if  ConfigurationSettings AppSettings  myKey      null       Now do your magic

User · Answer

if  ConfigurationManager AppSettings AllKeys Contains  myKey             Key exists   else          Key doesn t exist

User · Answer

Using the new c  syntax with TryParse worked well for me        TimeOut   if  int TryParse ConfigurationManager AppSettings  timeOut    out int timeOut            this timeOut   timeOut

User · Answer

Safely returned default value via generics and LINQ     public T ReadAppSetting lt T gt  string searchKey  T defaultValue  StringComparison compare   StringComparison Ordinal        if  ConfigurationManager AppSettings AllKeys Any key   gt  string Compare key  searchKey  compare     0             try              see if it can be converted              var converter   TypeDescriptor GetConverter typeof T                if  converter    null  defaultValue    T converter ConvertFromString ConfigurationManager AppSettings GetValues searchKey  First                       catch        nothing to do just return the defaultValue           return defaultValue      Used as follows   string LogFileName   ReadAppSetting  LogFile   LogFile    double DefaultWidth   ReadAppSetting  Width  1280 0   double DefaultHeight   ReadAppSetting  Height  1024 0   Color DefaultColor   ReadAppSetting  Color  Colors Black

User · Answer

I think the LINQ expression may be best      const string MyKey    myKey      if  ConfigurationManager AppSettings AllKeys Any key   gt  key    MyKey                                Key exists

User · Answer

Upper options gives flexible to all manner  if you know key type try parsing them bool TryParse ConfigurationManager AppSettings  myKey    out myvariable

[c#] How to check if an appSettings key exists?

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