初心 & 目标

很早就想通过阅读源码向大神学习了，但由于拖延一直未能开始，这次算是莽一波不再挑来挑去直接开读。

选择 Westwind.ApplicationConfiguration 的原因有三：最近在用，好奇某些问题它是如何解决的，代码量小。

预设目标：

跨项目引用同一配置是如何实现的？详见实现跨项目引用同一配置
XML Provider 为什么用起来总有问题？之前的用法错了
Utilities 的工具类有什么亮点？详见有亮点的代码片段
项目结构
Class Structure
This library consists of the main AppConfiguration class plus provider logic. Providers are based on a IConfigurationProvider interface with a ConfigurationProviderBase class providing base functionality.

Westwind.ApplicationConfiguration - 图1

解决方案

有亮点的代码片段

加密 & 解密

源码内完整的加密流程是：

传入对象及该对象需加密的属性（或字段）名
通过反射获取属性（或字段）值
将值转换为字符串（仅支持加密能转换为字符串的属性值）
Triple DES 加密字符串

下面展示 Encryption.cs 中用于 Triple DES 加密的代码片段：

/// <summary>
/// Encrypts a string using Triple DES encryption with a two way encryption key.
/// String is returned as Base64 encoded value rather than binary.
/// </summary>
/// <param name="inputString"></param>
/// <param name="encryptionKey"></param>
/// <returns></returns>
public static string EncryptString(string inputString, string encryptionKey)
{
    return Convert.ToBase64String(EncryptBytes(Encoding.ASCII.GetBytes(inputString), encryptionKey));
}
/// <summary>
/// Replace this value with some unique key of your own
/// Best set this in your App start up in a Static constructor
/// </summary>
public static string Key = "0a1f131c";
/// <summary>
/// Encodes a stream of bytes using DES encryption with a pass key. Lowest level method that 
/// handles all work.
/// </summary>
/// <param name="inputString"></param>
/// <param name="encryptionKey"></param>
/// <returns></returns>
public static byte[] EncryptBytes(byte[] inputString, string encryptionKey) 
{
    if (encryptionKey == null) encryptionKey = Key;
    var des =  new TripleDESCryptoServiceProvider();
    var hashmd5 = new MD5CryptoServiceProvider();
    des.Key = hashmd5.ComputeHash(Encoding.ASCII.GetBytes(encryptionKey));
    des.Mode = CipherMode.ECB;
    ICryptoTransform transform = des.CreateEncryptor();
    byte[] buffer = inputString;
    return transform.TransformFinalBlock(buffer,0,buffer.Length);
}

解密：

/// <summary>
/// Decrypts a string using DES encryption and a pass key that was used for 
/// encryption.
/// <seealso>Class wwEncrypt</seealso>
/// </summary>
/// <param name="decryptString"></param>
/// <param name="encryptionKey"></param>
/// <returns>String</returns>
public static string DecryptString(string decryptString, string encryptionKey)
{
    try
    {
        return Encoding.ASCII.GetString(DecryptBytes(Convert.FromBase64String(decryptString), encryptionKey));
    }
    catch
    {
        // Probably not encoded
        return string.Empty;
    }
}
/// <summary>
/// Decrypts a Byte array from DES with an Encryption Key.
/// </summary>
/// <param name="decryptBuffer"></param>
/// <param name="encryptionKey"></param>
/// <returns></returns>
public static byte[] DecryptBytes(byte[] decryptBuffer, string encryptionKey)
{
    if (decryptBuffer == null || decryptBuffer.Length == 0) return null;
    if (encryptionKey == null) encryptionKey = Key;
    var des = new TripleDESCryptoServiceProvider();
    var hashmd5 = new MD5CryptoServiceProvider();
    des.Key = hashmd5.ComputeHash(Encoding.ASCII.GetBytes(encryptionKey));
    des.Mode = CipherMode.ECB;
    // 创建解密器对象
    ICryptoTransform transform = des.CreateDecryptor();
    return transform.TransformFinalBlock(decryptBuffer, 0, decryptBuffer.Length);
}

通过反射实现的对象复制

源码：

public const BindingFlags MemberAccess =
    BindingFlags.Public | BindingFlags.NonPublic |
    BindingFlags.Static | BindingFlags.Instance | BindingFlags.IgnoreCase;
/// <summary>
/// Copies the content of one object to another. The target object 'pulls' properties of the first. 
/// </summary>
/// <param name="source"></param>
/// <param name="target"></param>
/// <param name="excludedProperties"></param>
public static void CopyObjectData(object source, Object target, string excludedProperties)
{
    CopyObjectData(source, target,excludedProperties, MemberAccess);
}
/// <summary>
/// Copies the data of one object to another. The target object 'pulls' properties of the first. 
/// This any matching properties are written to the target.
/// 
/// The object copy is a shallow copy only. Any nested types will be copied as 
/// whole values rather than individual property assignments (ie. via assignment)
/// </summary>
/// <param name="source">The source object to copy from</param>
/// <param name="target">The object to copy to</param>
/// <param name="excludedProperties">A comma delimited list of properties that should not be copied</param>
/// <param name="memberAccess">Reflection binding access</param>
public static void CopyObjectData(object source, object target, string excludedProperties, BindingFlags memberAccess)
{
    string[] excluded = null;
    if (!string.IsNullOrEmpty(excludedProperties))
    {
        excluded = excludedProperties.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
    }
    MemberInfo[] miTarget = target.GetType().GetMembers(memberAccess);
    foreach (MemberInfo field in miTarget)
    {
        string name = field.Name;
        // Skip over any property exceptions
        if (!string.IsNullOrEmpty(excludedProperties) && excluded.Contains(name))
            continue;
        if (field.MemberType == MemberTypes.Field)
        {
            FieldInfo sourceField = source.GetType().GetField(name);
            if (sourceField == null) continue;
            object sourceValue = sourceField.GetValue(source);
            ((FieldInfo)field).SetValue(target, sourceValue);
        }
        else if (field.MemberType == MemberTypes.Property)
        {
            PropertyInfo piSource = source.GetType().GetProperty(name, memberAccess);
            if (piSource == null) continue;
            PropertyInfo piTarget = field as PropertyInfo;
            if (piTarget != null && piTarget.CanWrite && piSource.CanRead)
            {
                object sourceValue = piSource.GetValue(source, null);
                piTarget.SetValue(target, sourceValue, null);
            }
        }
    }
}

调用时传入无需复制的属性或字段名（通过 , 分隔）：

DataUtils.CopyObjectData(newConfig, config, "Provider,ErrorMessage");

ReflectionUtils.cs 里面还有很多关于反射的应用。

常见类型与字符串间的转换

ConfigurationFileConfigurationProvider.cs 里面的 TypedValueToString 和 StringToTypedValue 方法实现了各种常见类型与 string 间的互相转换（并且考虑了 CultureInfo）：

/// <summary>
/// Converts a type to string if possible. This method supports an optional culture generically on any value.
/// It calls the ToString() method on common types and uses a type converter on all other objects
/// if available
/// </summary>
/// <param name="rawValue">The Value or Object to convert to a string</param>
/// <param name="culture">Culture for numeric and DateTime values</param>
/// <param name="unsupportedReturn">Return string for unsupported types</param>
/// <returns>string</returns>
private static string TypedValueToString(object rawValue, CultureInfo culture = null, string unsupportedReturn = null)
{
    if (rawValue == null) return string.Empty;
    if (culture == null) culture = CultureInfo.CurrentCulture;
    Type valueType = rawValue.GetType();
    string returnValue;
    if (valueType == typeof(string))
    {
        returnValue = rawValue as string;
    }
    else if (valueType == typeof(int) || valueType == typeof(decimal) ||
                valueType == typeof(double) || valueType == typeof(float) || valueType == typeof(Single))
    {
        returnValue = string.Format(culture.NumberFormat, "{0}", rawValue);
    }
    else if (valueType == typeof(DateTime))
    {
        returnValue = string.Format(culture.DateTimeFormat, "{0}", rawValue);
    }
    else if (valueType == typeof(bool) || valueType == typeof(Byte) || valueType.IsEnum)
    {
        returnValue = rawValue.ToString();
    }
    else if (valueType == typeof(byte[]))
    {
        returnValue = Convert.ToBase64String(rawValue as byte[]);
    }
    else if (valueType == typeof(Guid?))
    {
        if (rawValue == null)
        {
            returnValue = string.Empty;
        }
        else
        {
            return rawValue.ToString();
        }
    }
    else if (rawValue is IList)
    {
        return "ILIST_TYPE";
    }
    else
    {
        // Any type that supports a type converter
        TypeConverter converter = TypeDescriptor.GetConverter(valueType);
        if (converter != null && converter.CanConvertTo(typeof(string)) && converter.CanConvertFrom(typeof(string)))
        {
            returnValue = converter.ConvertToString(null, culture, rawValue);
        }
        else
        {
            // Last resort - just call ToString() on unknown type
            returnValue = !string.IsNullOrEmpty(unsupportedReturn) ? unsupportedReturn : rawValue.ToString();
        }
    }
    return returnValue;
}
/// <summary>
/// Turns a string into a typed value generically.
/// Explicitly assigns common types and falls back
/// on using type converters for unhandled types.         
/// <seealso>Class ReflectionUtils</seealso>
/// </summary>
/// <param name="sourceString"> The string to convert from </param>
/// <param name="targetType"> The type to convert to </param>
/// <param name="culture"> Culture used for numeric and datetime values. </param>
/// <returns>object. Throws exception if it cannot be converted.</returns>
private static object StringToTypedValue(string sourceString, Type targetType, CultureInfo culture = null)
{
    object result = null;
    bool isEmpty = string.IsNullOrEmpty(sourceString);
    if (culture == null) culture = CultureInfo.CurrentCulture;
    if (targetType == typeof(string))
    {
        result = sourceString;
    }
    else if (targetType == typeof(Int32) || targetType == typeof(int))
    {
        result = isEmpty ? 0 : Int32.Parse(sourceString, NumberStyles.Any, culture.NumberFormat);
    }
    else if (targetType == typeof(Int64))
    {
        result = isEmpty ? (Int64)0 : Int64.Parse(sourceString, NumberStyles.Any, culture.NumberFormat);
    }
    else if (targetType == typeof(Int16))
    {
        result = isEmpty ? (Int16)0 : Int16.Parse(sourceString, NumberStyles.Any, culture.NumberFormat);
    }
    else if (targetType == typeof(decimal))
    {
        result = isEmpty ? 0M : decimal.Parse(sourceString, NumberStyles.Any, culture.NumberFormat);
    }
    else if (targetType == typeof(DateTime))
    {
        result = isEmpty ? DateTime.MinValue : Convert.ToDateTime(sourceString, culture.DateTimeFormat);
    }
    else if (targetType == typeof(byte))
    {
        result = isEmpty ? 0 : Convert.ToByte(sourceString);
    }
    else if (targetType == typeof(double))
    {
        result = isEmpty ? 0F : Double.Parse(sourceString, NumberStyles.Any, culture.NumberFormat);
    }
    else if (targetType == typeof(Single))
    {
        result = isEmpty ? 0F : Single.Parse(sourceString, NumberStyles.Any, culture.NumberFormat);
    }
    else if (targetType == typeof(bool))
    {
        if (!isEmpty &&
            sourceString.ToLower() == "true" || sourceString.ToLower() == "on" || sourceString == "1")
        {
            result = true;
        }
        else
        {
            result = false;
        }
    }
    else if (targetType == typeof(Guid))
    {
        result = isEmpty ? Guid.Empty : new Guid(sourceString);
    }
    else if (targetType.IsEnum)
    {
        result = Enum.Parse(targetType, sourceString);
    }
    else if (targetType == typeof(byte[]))
    {
        result = Convert.FromBase64String(sourceString);
    }
    else if (targetType.Name.StartsWith("Nullable`"))
    {
        if (sourceString.ToLower() == "null" || sourceString == string.Empty)
        {
            result = null;
        }
        else
        {
            targetType = Nullable.GetUnderlyingType(targetType);
            result = StringToTypedValue(sourceString, targetType);
        }
    }
    else
    {
        // Check for TypeConverters or FromString static method
        TypeConverter converter = TypeDescriptor.GetConverter(targetType);
        if (converter != null && converter.CanConvertFrom(typeof(string)))
        {
            result = converter.ConvertFromString(null, culture, sourceString);
        }
        else
        {
            // Try to invoke a static FromString method if it exists
            try
            {
                var mi = targetType.GetMethod("FromString");
                if (mi != null)
                {
                    return mi.Invoke(null, new object[] { sourceString });
                }
            }
            catch
            {
                // ignore error and assume not supported 
            }
            Debug.Assert(false, $"Type Conversion not handled in StringToTypedValue for {targetType.Name} {sourceString}");
            //throw (new InvalidCastException(Resources.StringToTypedValueValueTypeConversionFailed + targetType.Name));
        }
    }
    return result;
}

实现跨项目引用同一配置

看 Westwind.ApplicationConfiguration 的介绍时就很好奇它是如何实现的多个项目可以引用同一个配置，而且在任意项目中都可以更新配置。

看了源码后才意识到是我想太多了，其实并不复杂，核心就在于 —— 保证不同项目能对同一个配置实体进行读写。

Westwind.ApplicationConfiguration 支持多个类型的配置实体，它们大致分为三类：

文件类，其本质就是一个 XML 或 Json 文件
数据库类，其本质就是数据库中的一张表
.NET config 类，根据项目类型不同，其本质就是一个 Web.config 或 App.config 文件
文件类
这是最简单的：

使用属性存储配置文件路径，保证读写的都是同一文件
读取配置对应 Open FileStream
写入配置对应 Write FileStream

数据库类
使用属性存储数据库连接字符串和表名，保证读写的都是同一张表
- 配置表只有两列，一列存配置名，一列存配置序列化后的字符串
- CREATE TABLE [{Tablename}] ( [id] [int] , [ConfigData] [ntext] )
读取配置对应 SELECT
写入配置对应 UPDATE

.NET config 类
首先要有个认知 —— .NET config 文件本质上是一个 XML 文件。
当指定了配置文件路径时底层逻辑和文件类相似
未指定配置文件路径时：
- 文件路径使用 AppDomain.CurrentDomain.SetupInformation.ConfigurationFile，保证读写同一文件
- 读取配置对应 XmlDocument.Load
- 写入配置对应 XmlDocument.Save

注：读写过程中还经常使用 ConfigurationManager.RefreshSection 来刷新配置的命名节，以保证配置的时效性。

编码技巧

方法返回值优先选择表征执行状态的值

很多方法既要返回执行结果又要返回执行状态（例如执行是否成功和状态代码等），对于这类方法推荐优先选择表征执行状态的值作为方法的返回值。

例如将对象序列化为字符串的 SerializeObject 方法执行后会有两个返回值，一是序列化是否成功（bool），二是序列化后得到的字符串（string）。在这种情况下有两种选择：

方法返回 string，序列化是否成功通过 out 传出
方法返回 bool，序列化字符串通过 out 传出

两种选择哪个更好，我们只需看看调用 SerializeObject 的代码便能理解：

// 方案 1
public static string SerializeObjectToString(object instance)
{
    var xmlResultString = SerializeObject(instance, out bool serializeSuccess);
    if (!serializeSuccess) return null;
    return xmlResultString;
}
// 方案 2
public static string SerializeObjectToString(object instance)
{
    if (!SerializeObject(instance, out string xmlResultString)) return null;
    return xmlResultString;
}

不难看出，对于即返回执行结果又返回执行状态的方法，因为调用方在调用它们时大概率会优先关心执行状态，在确定执行状态后才会去使用具体的执行结果，所以从调用方的角度来看方案 2 的 SerializeObject 用起来更顺手，代码也更简洁。

Westwind.ApplicationConfiguration

初心 & 目标

项目结构

Class Structure