有没有办法按名称而不是 C# 中的位置来格式化字符串？
在 python 中，我可以做类似这个例子的事情（无耻地从这里偷走）：
>>> print '%(language)s has %(#)03d quote types.' % \
{'language': "Python", "#": 2}
Python has 002 quote types.
有没有办法在 C# 中做到这一点？比如说：
String.Format("{some_variable}: {some_other_variable}", ...);
能够使用变量名来做到这一点会很好，但字典也是可以接受的。
没有用于处理此问题的内置方法。
string myString = "{foo} is {bar} and {yadi} is {yada}".Inject(o);
Status.Text = "{UserName} last logged in at {LastLoginDate}".FormatWith(user);
第三种改进方法部分基于上述两种方法，来自 Phil Haack
我有一个刚刚发布到我的博客的实现：http: //haacked.com/archive/2009/01/04/fun-with-named-formats-string-parsing-and-edge-cases.aspx
它解决了这些其他实现与大括号转义有关的一些问题。该帖子有详细信息。它也做 DataBinder.Eval 的事情，但仍然非常快。
两者都是通过Visual Studio 2015中的新Roslyn编译器引入的。
C# 6.0：
return "\{someVariable} and also \{someOtherVariable}"或者
return $"{someVariable} and also {someOtherVariable}"
来源：C#6.0 中的新功能
VB 14：
return $"{someVariable} and also {someOtherVariable}"
值得注意的功能（在 Visual Studio 2015 IDE 中）：
{index}有效，而且{(index + 1).ToString().Trim()}享受！（&点击VS中的“发送微笑”）
你也可以像这样使用匿名类型：
public string Format(string input, object p)
{
foreach (PropertyDescriptor prop in TypeDescriptor.GetProperties(p))
input = input.Replace("{" + prop.Name + "}", (prop.GetValue(p) ?? "(null)").ToString());
return input;
}
当然，如果您还想解析格式，则需要更多代码，但您可以使用此函数格式化字符串，例如：
Format("test {first} and {another}", new { first = "something", another = "something else" })
似乎没有开箱即用的方法。IFormatProvider不过，实现您自己的链接到IDictionaryfor 值的方法看起来是可行的。
var Stuff = new Dictionary<string, object> {
{ "language", "Python" },
{ "#", 2 }
};
var Formatter = new DictionaryFormatProvider();
// Interpret {0:x} where {0}=IDictionary and "x" is hash key
Console.WriteLine string.Format(Formatter, "{0:language} has {0:#} quote types", Stuff);
输出：
Python 有 2 种引用类型
需要注意的是，您不能 mix FormatProviders，因此不能同时使用花哨的文本格式。
框架本身不提供执行此操作的方法，但您可以查看 Scott Hanselman 的这篇文章。示例用法：
Person p = new Person();
string foo = p.ToString("{Money:C} {LastName}, {ScottName} {BirthDate}");
Assert.AreEqual("$3.43 Hanselman, {ScottName} 1/22/1974 12:00:00 AM", foo);
James Newton-King 的这段代码是相似的，并且适用于子属性和索引，
string foo = "Top result for {Name} was {Results[0].Name}".FormatWith(student));
James 的代码依赖System.Web.UI.DataBinder来解析字符串，并且需要引用 System.Web，这在非 Web 应用程序中有些人不喜欢这样做。
编辑：哦，如果您没有准备好具有属性的对象，它们可以很好地与匿名类型一起使用：
string name = ...;
DateTime date = ...;
string foo = "{Name} - {Birthday}".FormatWith(new { Name = name, Birthday = date });
请参阅https://stackoverflow.com/questions/271398?page=2#358259
使用链接到的扩展，您可以这样写：
var str = "{foo} {bar} {baz}".Format(foo=>"foo", bar=>2, baz=>new object());
你会得到"foo 2 System.Object“。
我认为你会得到最接近的是索引格式：
String.Format("{0} has {1} quote types.", "C#", "1");
还有 String.Replace()，如果您愿意分多个步骤进行操作并相信您不会在字符串的其他任何地方找到您的“变量”：
string MyString = "{language} has {n} quote types.";
MyString = MyString.Replace("{language}", "C#").Replace("{n}", "1");
扩展它以使用列表：
List<KeyValuePair<string, string>> replacements = GetFormatDictionary();
foreach (KeyValuePair<string, string> item in replacements)
{
MyString = MyString.Replace(item.Key, item.Value);
}
您也可以通过 Dictionary<string, string> 迭代它的 .Keys 集合来做到这一点，但是通过使用 List<KeyValuePair<string, string>> 我们可以利用 List 的 .ForEach() 方法并将其压缩回单线：
replacements.ForEach(delegate(KeyValuePair<string,string>) item) { MyString = MyString.Replace(item.Key, item.Value);});
lambda 会更简单，但我仍在使用 .Net 2.0。另请注意，.Replace() 迭代使用时性能并不出色，因为 .Net 中的字符串是不可变的。此外，这需要MyString以委托可以访问的方式定义变量，因此它还不完美。
我的开源库Regextra支持命名格式（除其他外）。它目前面向 .NET 4.0+，可在NuGet上使用。我还有一篇关于它的介绍性博客文章：Regextra：帮助您减少（问题）{2}。
命名格式化位支持：
例子：
var order = new
{
Description = "Widget",
OrderDate = DateTime.Now,
Details = new
{
UnitPrice = 1500
}
};
string template = "We just shipped your order of '{Description}', placed on {OrderDate:d}. Your {{credit}} card will be billed {Details.UnitPrice:C}.";
string result = Template.Format(template, order);
// or use the extension: template.FormatTemplate(order);
结果：
我们刚刚发货了您在 2014 年 2 月 28 日下的“小部件”订单。您的 {credit} 卡将被收取 1,500.00 美元的费用。
查看项目的 GitHub 链接（上图）和 wiki 以获取其他示例。
private static Regex s_NamedFormatRegex = new Regex(@"\{(?!\{)(?<key>[\w]+)(:(?<fmt>(\{\{|\}\}|[^\{\}])*)?)?\}", RegexOptions.Compiled);
public static StringBuilder AppendNamedFormat(this StringBuilder builder,IFormatProvider provider, string format, IDictionary<string, object> args)
{
if (builder == null) throw new ArgumentNullException("builder");
var str = s_NamedFormatRegex.Replace(format, (mt) => {
string key = mt.Groups["key"].Value;
string fmt = mt.Groups["fmt"].Value;
object value = null;
if (args.TryGetValue(key,out value)) {
return string.Format(provider, "{0:" + fmt + "}", value);
} else {
return mt.Value;
}
});
builder.Append(str);
return builder;
}
public static StringBuilder AppendNamedFormat(this StringBuilder builder, string format, IDictionary<string, object> args)
{
if (builder == null) throw new ArgumentNullException("builder");
return builder.AppendNamedFormat(null, format, args);
}
例子：
var builder = new StringBuilder();
builder.AppendNamedFormat(
@"你好,{Name},今天是{Date:yyyy/MM/dd}, 这是你第{LoginTimes}次登录，积分{Score:{{ 0.00 }}}",
new Dictionary<string, object>() {
{ "Name", "wayjet" },
{ "LoginTimes",18 },
{ "Score", 100.4 },
{ "Date",DateTime.Now }
});
输出：你好，wayjet，今天是2011-05-04，这是你第18次登录，积分{ 100.40 }
检查这个：
public static string StringFormat(string format, object source)
{
var matches = Regex.Matches(format, @"\{(.+?)\}");
List<string> keys = (from Match matche in matches select matche.Groups[1].Value).ToList();
return keys.Aggregate(
format,
(current, key) =>
{
int colonIndex = key.IndexOf(':');
return current.Replace(
"{" + key + "}",
colonIndex > 0
? DataBinder.Eval(source, key.Substring(0, colonIndex), "{0:" + key.Substring(colonIndex + 1) + "}")
: DataBinder.Eval(source, key).ToString());
});
}
样本：
string format = "{foo} is a {bar} is a {baz} is a {qux:#.#} is a really big {fizzle}";
var o = new { foo = 123, bar = true, baz = "this is a test", qux = 123.45, fizzle = DateTime.Now };
Console.WriteLine(StringFormat(format, o));
与其他解决方案相比，性能相当不错。
我怀疑这是否可能。首先想到的是如何访问局部变量名？
然而，可能有一些巧妙的方法使用 LINQ 和 Lambda 表达式来做到这一点。
这是我不久前做的一个。它使用带有单个参数的 Format 方法扩展 String。好处是它会使用标准的 string.Format，如果你提供一个简单的参数，比如 int，但如果你使用匿名类型，它也可以工作。
示例用法：
"The {Name} family has {Children} children".Format(new { Children = 4, Name = "Smith" })
将导致“史密斯一家有 4 个孩子”。
它不会做疯狂的绑定东西，比如数组和索引器。但它是超级简单和高性能。
public static class AdvancedFormatString
{
/// <summary>
/// An advanced version of string.Format. If you pass a primitive object (string, int, etc), it acts like the regular string.Format. If you pass an anonmymous type, you can name the paramters by property name.
/// </summary>
/// <param name="formatString"></param>
/// <param name="arg"></param>
/// <returns></returns>
/// <example>
/// "The {Name} family has {Children} children".Format(new { Children = 4, Name = "Smith" })
///
/// results in
/// "This Smith family has 4 children
/// </example>
public static string Format(this string formatString, object arg, IFormatProvider format = null)
{
if (arg == null)
return formatString;
var type = arg.GetType();
if (Type.GetTypeCode(type) != TypeCode.Object || type.IsPrimitive)
return string.Format(format, formatString, arg);
var properties = TypeDescriptor.GetProperties(arg);
return formatString.Format((property) =>
{
var value = properties[property].GetValue(arg);
return Convert.ToString(value, format);
});
}
public static string Format(this string formatString, Func<string, string> formatFragmentHandler)
{
if (string.IsNullOrEmpty(formatString))
return formatString;
Fragment[] fragments = GetParsedFragments(formatString);
if (fragments == null || fragments.Length == 0)
return formatString;
return string.Join(string.Empty, fragments.Select(fragment =>
{
if (fragment.Type == FragmentType.Literal)
return fragment.Value;
else
return formatFragmentHandler(fragment.Value);
}).ToArray());
}
private static Fragment[] GetParsedFragments(string formatString)
{
Fragment[] fragments;
if ( parsedStrings.TryGetValue(formatString, out fragments) )
{
return fragments;
}
lock (parsedStringsLock)
{
if ( !parsedStrings.TryGetValue(formatString, out fragments) )
{
fragments = Parse(formatString);
parsedStrings.Add(formatString, fragments);
}
}
return fragments;
}
private static Object parsedStringsLock = new Object();
private static Dictionary<string,Fragment[]> parsedStrings = new Dictionary<string,Fragment[]>(StringComparer.Ordinal);
const char OpeningDelimiter = '{';
const char ClosingDelimiter = '}';
/// <summary>
/// Parses the given format string into a list of fragments.
/// </summary>
/// <param name="format"></param>
/// <returns></returns>
static Fragment[] Parse(string format)
{
int lastCharIndex = format.Length - 1;
int currFragEndIndex;
Fragment currFrag = ParseFragment(format, 0, out currFragEndIndex);
if (currFragEndIndex == lastCharIndex)
{
return new Fragment[] { currFrag };
}
List<Fragment> fragments = new List<Fragment>();
while (true)
{
fragments.Add(currFrag);
if (currFragEndIndex == lastCharIndex)
{
break;
}
currFrag = ParseFragment(format, currFragEndIndex + 1, out currFragEndIndex);
}
return fragments.ToArray();
}
/// <summary>
/// Finds the next delimiter from the starting index.
/// </summary>
static Fragment ParseFragment(string format, int startIndex, out int fragmentEndIndex)
{
bool foundEscapedDelimiter = false;
FragmentType type = FragmentType.Literal;
int numChars = format.Length;
for (int i = startIndex; i < numChars; i++)
{
char currChar = format[i];
bool isOpenBrace = currChar == OpeningDelimiter;
bool isCloseBrace = isOpenBrace ? false : currChar == ClosingDelimiter;
if (!isOpenBrace && !isCloseBrace)
{
continue;
}
else if (i < (numChars - 1) && format[i + 1] == currChar)
{//{{ or }}
i++;
foundEscapedDelimiter = true;
}
else if (isOpenBrace)
{
if (i == startIndex)
{
type = FragmentType.FormatItem;
}
else
{
if (type == FragmentType.FormatItem)
throw new FormatException("Two consequtive unescaped { format item openers were found. Either close the first or escape any literals with another {.");
//curr character is the opening of a new format item. so we close this literal out
string literal = format.Substring(startIndex, i - startIndex);
if (foundEscapedDelimiter)
literal = ReplaceEscapes(literal);
fragmentEndIndex = i - 1;
return new Fragment(FragmentType.Literal, literal);
}
}
else
{//close bracket
if (i == startIndex || type == FragmentType.Literal)
throw new FormatException("A } closing brace existed without an opening { brace.");
string formatItem = format.Substring(startIndex + 1, i - startIndex - 1);
if (foundEscapedDelimiter)
formatItem = ReplaceEscapes(formatItem);//a format item with a { or } in its name is crazy but it could be done
fragmentEndIndex = i;
return new Fragment(FragmentType.FormatItem, formatItem);
}
}
if (type == FragmentType.FormatItem)
throw new FormatException("A format item was opened with { but was never closed.");
fragmentEndIndex = numChars - 1;
string literalValue = format.Substring(startIndex);
if (foundEscapedDelimiter)
literalValue = ReplaceEscapes(literalValue);
return new Fragment(FragmentType.Literal, literalValue);
}
/// <summary>
/// Replaces escaped brackets, turning '{{' and '}}' into '{' and '}', respectively.
/// </summary>
/// <param name="value"></param>
/// <returns></returns>
static string ReplaceEscapes(string value)
{
return value.Replace("{{", "{").Replace("}}", "}");
}
private enum FragmentType
{
Literal,
FormatItem
}
private class Fragment
{
public Fragment(FragmentType type, string value)
{
Type = type;
Value = value;
}
public FragmentType Type
{
get;
private set;
}
/// <summary>
/// The literal value, or the name of the fragment, depending on fragment type.
/// </summary>
public string Value
{
get;
private set;
}
}
}
这是任何对象的简单方法：
using System.Text.RegularExpressions;
using System.ComponentModel;
public static string StringWithFormat(string format, object args)
{
Regex r = new Regex(@"\{([A-Za-z0-9_]+)\}");
MatchCollection m = r.Matches(format);
var properties = TypeDescriptor.GetProperties(args);
foreach (Match item in m)
{
try
{
string propertyName = item.Groups[1].Value;
format = format.Replace(item.Value, properties[propertyName].GetValue(args).ToString());
}
catch
{
throw new FormatException("The format string is not valid");
}
}
return format;
}
以及如何使用它：
DateTime date = DateTime.Now;
string dateString = StringWithFormat("{Month}/{Day}/{Year}", date);
输出：2/27/2012
我实现了这是一个简单的类，它复制了 String.Format 的功能（使用类时除外）。您可以使用字典或类型来定义字段。
https://github.com/SergueiFedorov/NamedFormatString
C# 6.0 正在将此功能添加到语言规范中，以便NamedFormatString向后兼容。
我以与现有解决方案略有不同的方式解决了这个问题。它完成了命名项目替换的核心（不是某些人所做的反射位）。它非常快速和简单......这是我的解决方案：
/// <summary>
/// Formats a string with named format items given a template dictionary of the items values to use.
/// </summary>
public class StringTemplateFormatter
{
private readonly IFormatProvider _formatProvider;
/// <summary>
/// Constructs the formatter with the specified <see cref="IFormatProvider"/>.
/// This is defaulted to <see cref="CultureInfo.CurrentCulture">CultureInfo.CurrentCulture</see> if none is provided.
/// </summary>
/// <param name="formatProvider"></param>
public StringTemplateFormatter(IFormatProvider formatProvider = null)
{
_formatProvider = formatProvider ?? CultureInfo.CurrentCulture;
}
/// <summary>
/// Formats a string with named format items given a template dictionary of the items values to use.
/// </summary>
/// <param name="text">The text template</param>
/// <param name="templateValues">The named values to use as replacements in the formatted string.</param>
/// <returns>The resultant text string with the template values replaced.</returns>
public string FormatTemplate(string text, Dictionary<string, object> templateValues)
{
var formattableString = text;
var values = new List<object>();
foreach (KeyValuePair<string, object> value in templateValues)
{
var index = values.Count;
formattableString = ReplaceFormattableItem(formattableString, value.Key, index);
values.Add(value.Value);
}
return String.Format(_formatProvider, formattableString, values.ToArray());
}
/// <summary>
/// Convert named string template item to numbered string template item that can be accepted by <see cref="string.Format(string,object[])">String.Format</see>
/// </summary>
/// <param name="formattableString">The string containing the named format item</param>
/// <param name="itemName">The name of the format item</param>
/// <param name="index">The index to use for the item value</param>
/// <returns>The formattable string with the named item substituted with the numbered format item.</returns>
private static string ReplaceFormattableItem(string formattableString, string itemName, int index)
{
return formattableString
.Replace("{" + itemName + "}", "{" + index + "}")
.Replace("{" + itemName + ",", "{" + index + ",")
.Replace("{" + itemName + ":", "{" + index + ":");
}
}
它以下列方式使用：
[Test]
public void FormatTemplate_GivenANamedGuid_FormattedWithB_ShouldFormatCorrectly()
{
// Arrange
var template = "My guid {MyGuid:B} is awesome!";
var templateValues = new Dictionary<string, object> { { "MyGuid", new Guid("{A4D2A7F1-421C-4A1D-9CB2-9C2E70B05E19}") } };
var sut = new StringTemplateFormatter();
// Act
var result = sut.FormatTemplate(template, templateValues);
//Assert
Assert.That(result, Is.EqualTo("My guid {a4d2a7f1-421c-4a1d-9cb2-9c2e70b05e19} is awesome!"));
}
希望有人觉得这很有用！
即使接受的答案给出了一些很好的例子，.Inject 以及一些 Haack 例子都不能处理转义。许多人还严重依赖 Regex（较慢）或 DataBinder.Eval，这在 .NET Core 和其他一些环境中不可用。
考虑到这一点，我编写了一个简单的基于状态机的解析器，它通过字符流式传输StringBuilder，逐个字符地写入输出。它被实现为String扩展方法，并且可以将 aDictionary<string, object>或objectwith 参数作为输入（使用反射）。
当输入包含不平衡的大括号和/或其他错误时，它处理无限级别{{{escaping}}}和抛出。FormatException
public static class StringExtension {
/// <summary>
/// Extension method that replaces keys in a string with the values of matching object properties.
/// </summary>
/// <param name="formatString">The format string, containing keys like {foo} and {foo:SomeFormat}.</param>
/// <param name="injectionObject">The object whose properties should be injected in the string</param>
/// <returns>A version of the formatString string with keys replaced by (formatted) key values.</returns>
public static string FormatWith(this string formatString, object injectionObject) {
return formatString.FormatWith(GetPropertiesDictionary(injectionObject));
}
/// <summary>
/// Extension method that replaces keys in a string with the values of matching dictionary entries.
/// </summary>
/// <param name="formatString">The format string, containing keys like {foo} and {foo:SomeFormat}.</param>
/// <param name="dictionary">An <see cref="IDictionary"/> with keys and values to inject into the string</param>
/// <returns>A version of the formatString string with dictionary keys replaced by (formatted) key values.</returns>
public static string FormatWith(this string formatString, IDictionary<string, object> dictionary) {
char openBraceChar = '{';
char closeBraceChar = '}';
return FormatWith(formatString, dictionary, openBraceChar, closeBraceChar);
}
/// <summary>
/// Extension method that replaces keys in a string with the values of matching dictionary entries.
/// </summary>
/// <param name="formatString">The format string, containing keys like {foo} and {foo:SomeFormat}.</param>
/// <param name="dictionary">An <see cref="IDictionary"/> with keys and values to inject into the string</param>
/// <returns>A version of the formatString string with dictionary keys replaced by (formatted) key values.</returns>
public static string FormatWith(this string formatString, IDictionary<string, object> dictionary, char openBraceChar, char closeBraceChar) {
string result = formatString;
if (dictionary == null || formatString == null)
return result;
// start the state machine!
// ballpark output string as two times the length of the input string for performance (avoids reallocating the buffer as often).
StringBuilder outputString = new StringBuilder(formatString.Length * 2);
StringBuilder currentKey = new StringBuilder();
bool insideBraces = false;
int index = 0;
while (index < formatString.Length) {
if (!insideBraces) {
// currently not inside a pair of braces in the format string
if (formatString[index] == openBraceChar) {
// check if the brace is escaped
if (index < formatString.Length - 1 && formatString[index + 1] == openBraceChar) {
// add a brace to the output string
outputString.Append(openBraceChar);
// skip over braces
index += 2;
continue;
}
else {
// not an escaped brace, set state to inside brace
insideBraces = true;
index++;
continue;
}
}
else if (formatString[index] == closeBraceChar) {
// handle case where closing brace is encountered outside braces
if (index < formatString.Length - 1 && formatString[index + 1] == closeBraceChar) {
// this is an escaped closing brace, this is okay
// add a closing brace to the output string
outputString.Append(closeBraceChar);
// skip over braces
index += 2;
continue;
}
else {
// this is an unescaped closing brace outside of braces.
// throw a format exception
throw new FormatException($"Unmatched closing brace at position {index}");
}
}
else {
// the character has no special meaning, add it to the output string
outputString.Append(formatString[index]);
// move onto next character
index++;
continue;
}
}
else {
// currently inside a pair of braces in the format string
// found an opening brace
if (formatString[index] == openBraceChar) {
// check if the brace is escaped
if (index < formatString.Length - 1 && formatString[index + 1] == openBraceChar) {
// there are escaped braces within the key
// this is illegal, throw a format exception
throw new FormatException($"Illegal escaped opening braces within a parameter - index: {index}");
}
else {
// not an escaped brace, we have an unexpected opening brace within a pair of braces
throw new FormatException($"Unexpected opening brace inside a parameter - index: {index}");
}
}
else if (formatString[index] == closeBraceChar) {
// handle case where closing brace is encountered inside braces
// don't attempt to check for escaped braces here - always assume the first brace closes the braces
// since we cannot have escaped braces within parameters.
// set the state to be outside of any braces
insideBraces = false;
// jump over brace
index++;
// at this stage, a key is stored in current key that represents the text between the two braces
// do a lookup on this key
string key = currentKey.ToString();
// clear the stringbuilder for the key
currentKey.Clear();
object outObject;
if (!dictionary.TryGetValue(key, out outObject)) {
// the key was not found as a possible replacement, throw exception
throw new FormatException($"The parameter \"{key}\" was not present in the lookup dictionary");
}
// we now have the replacement value, add the value to the output string
outputString.Append(outObject);
// jump to next state
continue;
} // if }
else {
// character has no special meaning, add it to the current key
currentKey.Append(formatString[index]);
// move onto next character
index++;
continue;
} // else
} // if inside brace
} // while
// after the loop, if all braces were balanced, we should be outside all braces
// if we're not, the input string was misformatted.
if (insideBraces) {
throw new FormatException("The format string ended before the parameter was closed.");
}
return outputString.ToString();
}
/// <summary>
/// Creates a Dictionary from an objects properties, with the Key being the property's
/// name and the Value being the properties value (of type object)
/// </summary>
/// <param name="properties">An object who's properties will be used</param>
/// <returns>A <see cref="Dictionary"/> of property values </returns>
private static Dictionary<string, object> GetPropertiesDictionary(object properties) {
Dictionary<string, object> values = null;
if (properties != null) {
values = new Dictionary<string, object>();
PropertyDescriptorCollection props = TypeDescriptor.GetProperties(properties);
foreach (PropertyDescriptor prop in props) {
values.Add(prop.Name, prop.GetValue(properties));
}
}
return values;
}
}
最终，所有的逻辑都归结为 10 个主要状态 - 因为当状态机在括号外并且同样在括号内时，下一个字符是左大括号、转义左大括号、闭大括号、转义闭大括号，或者一个普通的角色。随着循环的进行，这些条件中的每一个都会单独处理，将字符添加到 outputStringBuffer或 key StringBuffer。当参数关闭时，键StringBuffer的值用于在字典中查找参数的值，然后将其推入输出StringBuffer。StringBuffer最后，返回输出的值。
string language = "Python";
int numquotes = 2;
string output = language + " has "+ numquotes + " language types.";
编辑：我应该说的是，“不，我不相信 C# 支持你想要做的事情。这与你将得到的一样接近。”