当我破解我们的代码库时,我才注意到这个函数.它将IDictionary<string, object>(Paramters - 一个实例变量)转换为XML字符串.
这只不过是我的好奇心:-).
那么使用C#4.0可以用更少的代码编写吗？规则:除了.Net Framework BCL之外没有外部库.
为了使它更具挑战性,我不会在这里输入输入字典规范,因为你应该能够从代码中解决它.
public string ConvertToXml() {
XmlDocument doc = new XmlDocument();
doc.LoadXml("<?xml version='1.0' encoding='utf-8'?><sc/>");
foreach (KeyValuePair<string, object> param in Parameters) {
XmlElement elm = doc.CreateElement("pr");
if (param.Value is int || param.Value is Int32 || param.Value is Int16 || param.Value is Int64) {
elm.SetAttribute("tp", "int");
} else if (param.Value is DateTime?){
elm.SetAttribute("tp", "datetime");
} else {
elm.SetAttribute("tp", "string");
}
elm.SetAttribute("nm", param.Key);
if (param.Value is DateTime?) {
DateTime? dateTime = param.Value as DateTime?;
elm.SetAttribute("vl", dateTime.Value.ToString("o"));
} else{
elm.SetAttribute("vl", param.Value.ToString());
}
doc.FirstChild.NextSibling.AppendChild(elm);
}
return doc.OuterXml;
}
让我补充一些想法.
对我来说 :
使用LINQ to XML可以使编写起来非常简单.如果您有选择,请优先使用标准XML库.
我相信这应该是等价的:
public static string ToXmlString(this IDictionary<string, object> dict)
{
var doc = new XDocument(new XElement("sc", dict.Select(ToXElement)));
using (var writer = new Utf8StringWriter())
{
doc.Save(writer); // "hack" to force include the declaration
return writer.ToString();
}
}
class Utf8StringWriter : StringWriter
{
public override Encoding Encoding { get { return Encoding.UTF8; } }
}
static XElement ToXElement(KeyValuePair<string, object> kvp)
{
var value = kvp.Value ?? String.Empty;
string typeString;
string valueString;
switch (Type.GetTypeCode(value.GetType()))
{
case TypeCode.Int16:
case TypeCode.Int32:
case TypeCode.Int64:
typeString = "int";
valueString = value.ToString();
break;
case TypeCode.DateTime:
typeString = "datetime";
valueString = ((DateTime)value).ToString("o");
break;
default:
typeString = "string";
valueString = value.ToString();
break;
}
return new XElement("pr",
new XAttribute("tp", typeString),
new XAttribute("nm", kvp.Key),
new XAttribute("vl", valueString));
}
请注意,检查值是否类型DateTime?是没有意义的.我不确定null在字典中存储值有什么价值但是如果可能的话,你会因为制作类型的值而失去那种类型的信息object.
此外,如果有一个DateTime?值不是null,那么值本身将被装箱,而不是Nullable<DateTime>结构本身.所以实际的类型将DateTime是这个代码工作的原因.
使用动态和LINQ to XML:
ConvertToXml可以简化为一个语句(假设省略XML声明是可以接受的).
public string ConvertToXml()
{
return new XElement("sc",
Parameters.Select(param => CreateElement(param.Key, (dynamic)param.Value))
).ToString(SaveOptions.DisableFormatting);
}
请注意,CreateElement将param.Value强制转换为动态,以便在运行时选择以下正确的重载.
XElement CreateElement(string key, object value)
{
return CreateElement("string", key, value.ToString());
}
XElement CreateElement(string key, long value)
{
return CreateElement("int", key, value.ToString());
}
XElement CreateElement(string key, DateTime value)
{
return CreateElement("datetime", key, value.ToString("o"));
}
上面的重载最终会调用:
XElement CreateElement(string typename, string key, string value)
{
return new XElement("pr",
new XAttribute("tp", typename),
new XAttribute("nm", key),
new XAttribute("vl", value)
);
}
此代码减少了问题中的语句数(尽管不是行).这种方法建立在svick的基础之上,但减少了所需的方法和动态调用的数量.
使用.net 4.0等功能Tuple和dynamic关键字.我的测试用例产生了原始问题的精确输出.
//using System;
//using System.Collections.Generic;
//using System.Linq;
//using System.Xml.Linq;
public string ConvertToXml()
{
//Create XDocument to specification with linq-to-xml
var doc = new XDocument(
new XElement("sc",
from param in Parameters
//Uses dynamic invocation to use overload resolution at runtime
let attributeVals = AttributeValues((dynamic)param.Value)
select new XElement("pr",
new XAttribute("tp", attributeVals.Item1),
new XAttribute("nm", param.Key),
new XAttribute("vl", attributeVals.Item2)
)
)
);
//Write to string
using (var writer = new Utf8StringWriter())
{
doc.Save(writer, SaveOptions.DisableFormatting);//Don't add whitespace
return writer.ToString();
}
}
//C# overloading will choose `long` as the best pick for `short` and `int` types too
static Tuple<string, string> AttributeValues(long value)
{
return Tuple.Create("int", value.ToString());
}
//Overload for DateTime
static Tuple<string, string> AttributeValues(DateTime value)
{
return Tuple.Create("datetime", value.ToString("o"));
}
//Overload catch all
static Tuple<string, string> AttributeValues(object value)
{
return Tuple.Create("string", value.ToString());
}
// Using John Skeet's Utf8StringWriter trick
// http://stackoverflow.com/questions/3871738/force-xdocument-to-write-to-string-with-utf-8-encoding/3871822#3871822
class Utf8StringWriter : System.IO.StringWriter
{
public override System.Text.Encoding Encoding { get { return System.Text.Encoding.UTF8; } }
}
可选:将 let语句更改为:
let attributeVals = (Tuple<string,string>)AttributeValues((dynamic)param.Value)
这会将动态调用限制在该行.但由于没有其他事情发生,我认为不想添加额外的演员会更干净.
public string ConvertToXml()
{
var doc = new XDocument(
new XElement("sd",
Parameters.Select(param =>
new XElement("pr",
new XAttribute("tp", GetTypeName((dynamic)param.Value)),
new XAttribute("nm", param.Key),
new XAttribute("vl", GetValue((dynamic)param.Value))
)
)
)
);
return doc.ToString();
}
此代码假定您已重载方法GetTypeName()并GetValue()实现为:
static string GetTypeName(long value)
{
return "int";
}
static string GetTypeName(DateTime? value)
{
return "datetime";
}
static string GetTypeName(object value)
{
return "string";
}
static string GetValue(DateTime? value)
{
return value.Value.ToString("o");
}
static string GetValue(object value)
{
return value.ToString();
}
这使用了这样的事实:在使用时dynamic,将在运行时选择正确的重载.
你并不需要过载int和short,因为它们可以被转换成long(并且这样的转换被认为是比转换,以更好object).但是,这也意味着,类型,如ushort和byte将得到tp的int.
此外,返回的字符串不包含XML声明,但无论如何声明UTF-16编码的字符串是UTF-8编码也没有意义.(如果您希望稍后将其保存在UTF-8编码文件中,则返回并保存XDocument将更好,并将编写正确的XML声明.)
我觉得这是一个很好的解决方案,因为它很好地分离问题纳入不同的方法(你甚至可以把GetTypeName()和GetValue()超载成不同的类).