AppSettingsReader.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / fx / src / CompMod / System / Configuration / AppSettingsReader.cs / 1 / AppSettingsReader.cs
                        

                        
                            //------------------------------------------------------------------------------ 
// 
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//----------------------------------------------------------------------------- 

using System; 
using System.Reflection; 
using System.Configuration;
using System.Collections.Specialized; 
using System.Globalization;

namespace System.Configuration {
 
    /// 
    ///     The AppSettingsReader class provides a wrapper for System.Configuration.ConfigurationManager.AppSettings 
    ///     which provides a single method for reading values from the config file of a particular type. 
    /// 
    public class AppSettingsReader { 
        private NameValueCollection map;
        static Type stringType = typeof(string);
        static Type[] paramsArray = new Type[] { stringType };
        static string NullString = "None"; 

        ///  
        ///     Constructor 
        /// 
        public AppSettingsReader() { 
            map = System.Configuration.ConfigurationManager.AppSettings;
        }

        ///  
        ///     Gets the value for specified key from ConfigurationManager.AppSettings, and returns
        ///     an object of the specified type containing the value from the config file.  If the key 
        ///     isn't in the config file, or if it is not a valid value for the given type, it will 
        ///     throw an exception with a descriptive message so the user can make the appropriate
        ///     change 
        /// 
        public object GetValue(string key, Type type) {
            if (key == null) throw new ArgumentNullException("key");
            if (type == null) throw new ArgumentNullException("type"); 

            string val = map[key]; 
 
            if (val == null) throw new InvalidOperationException(SR.GetString(SR.AppSettingsReaderNoKey, key));
 
            if (type == stringType) {
                // It's a string, so we can ALMOST just return the value.  The only
                // tricky point is that if it's the string "(None)", then we want to
                // return null.  And of course we need a way to represent the string 
                // (None), so we use ((None)), and so on... so it's a little complicated.
                int NoneNesting = GetNoneNesting(val); 
                if (NoneNesting == 0) { 
                    // val is not of the form ((..((None))..))
                    return val; 
                }
                else if (NoneNesting == 1) {
                    // val is (None)
                    return null; 
                }
                else { 
                    // val is of the form ((..((None))..)) 
                    return val.Substring(1, val.Length - 2);
                } 
            }
            else {
                try {
                    return Convert.ChangeType(val, type, CultureInfo.InvariantCulture); 
                } catch (Exception) {
                    string displayString = (val.Length == 0) ? SR.AppSettingsReaderEmptyString : val; 
                    throw new InvalidOperationException(SR.GetString(SR.AppSettingsReaderCantParse, displayString, key, type.ToString())); 
                }
            } 
        }

        private int GetNoneNesting(string val) {
            int count = 0; 
            int len = val.Length;
            if (len > 1) { 
                while (val[count] == '(' && val[len - count - 1] == ')') { 
                    count++;
                } 
                if (count > 0 && string.Compare(NullString, 0, val, count, len - 2 * count, StringComparison.Ordinal) != 0) {
                    // the stuff between the parens is not "None"
                    count = 0;
                } 
            }
            return count; 
        } 
    }
}

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