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//------------------------------------------------------------------------------
// <copyright file="AppSettingsReader.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
//------------------------------------------------------------------------------
using System;
using System.Reflection;
using System.Configuration;
using System.Collections.Specialized;
using System.Globalization;
namespace System.Configuration {
/// <devdoc>
/// 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.
/// </devdoc>
public class AppSettingsReader {
private NameValueCollection map;
static Type stringType = typeof(string);
static Type[] paramsArray = new Type[] { stringType };
static string NullString = "None";
/// <devdoc>
/// Constructor
/// </devdoc>
public AppSettingsReader() {
map = System.Configuration.ConfigurationManager.AppSettings;
}
/// <devdoc>
/// 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
/// </devdoc>
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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