有没有办法按名称格式化字符串而不是在C＃中定位？
在python中，我可以做类似这个例子的事情（从here无耻地被盗）：
>>> print '%(language)s has %(#)03d quote types.' % \
{'language': "Python", "#": 2}
Python has 002 quote types.
有没有办法在C＃中这样做？比如说：
String.Format("{some_variable}: {some_other_variable}", ...);
能够使用变量名称执行此操作会很好，但字典也可以接受。
答案 0 :(得分：127)
没有内置的处理方法。
string myString = "{foo} is {bar} and {yadi} is {yada}".Inject(o);
Status.Text = "{UserName} last logged in at {LastLoginDate}".FormatWith(user);
答案 1 :(得分：45)
我刚刚在我的博客上发布了一个实现：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。帖子有详细信息。它也可以执行DataBinder.Eval，但仍然非常快。
答案 2 :(得分：40)
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
return $"{someVariable} and also {someOtherVariable}"
VB 14：
return $"{someVariable} and also {someOtherVariable}"
值得注意的功能（在Visual Studio 2015 IDE中）：
{index}有用，还有{(index + 1).ToString().Trim()} 享受！ （并点击VS中的“发送微笑”）
答案 3 :(得分：39)
你也可以使用这样的匿名类型：
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化，则需要更多代码，但您可以使用以下函数格式化字符串：
Format("test {first} and {another}", new { first = "something", another = "something else" })
答案 4 :(得分：14)
似乎没有办法开箱即用。但是，实现您自己的IFormatProvider链接到IDictionary的值是可行的。
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 has 2 quote types
需要注意的是，您无法混合FormatProviders，因此不能同时使用花哨的文本格式。
答案 5 :(得分：9)
框架本身并没有提供这样做的方法，但你可以看看Scott Hanselman的this post。用法示例：
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);
This code类似于子属性和索引，
string foo = "Top result for {Name} was {Results[0].Name}".FormatWith(student));
James的代码依赖于 System.Web.UI.DataBinder 来解析字符串，并且需要引用System.Web，有些人不喜欢在非Web应用程序中这样做。
编辑：哦，如果你没有准备好属性的对象，他们可以很好地使用匿名类型：
string name = ...;
DateTime date = ...;
string foo = "{Name} - {Birthday}".FormatWith(new { Name = name, Birthday = date });
答案 6 :(得分：6)
请参阅https://stackoverflow.com/questions/271398?page=2#358259
使用链接到扩展名，您可以写下：
var str = "{foo} {bar} {baz}".Format(foo=>"foo", bar=>2, baz=>new object());
你会得到"foo 2 System.Object“。
答案 7 :(得分：4)
我认为你得到的最接近的是索引格式：
String.Format("{0} has {1} quote types.", "C#", "1");
还有String.Replace（），如果你愿意在多个步骤中执行它，并认为你不会在字符串中的任何其他地方找到你的'变量'：
string MyString = "{language} has {n} quote types.";
MyString = MyString.Replace("{language}", "C#").Replace("{n}", "1");
扩展此项以使用列表：
List<KeyValuePair<string, string>> replacements = GetFormatDictionary();
foreach (KeyValuePair<string, string> item in replacements)
{
MyString = MyString.Replace(item.Key, item.Value);
}
你可以用Dictionary＆lt; string，string＆gt;来做到这一点。也可以通过迭代它的.Keys集合，但是使用List＆lt; KeyValuePair＆lt; string，string＆gt;＆gt;我们可以利用List的.ForEach（）方法并将其浓缩回一行：
replacements.ForEach(delegate(KeyValuePair<string,string>) item) { MyString = MyString.Replace(item.Key, item.Value);});
lambda会更简单，但我仍然使用.Net 2.0。另请注意，迭代使用时，.Replace（）性能不是很好，因为.Net中的字符串是不可变的。此外，这需要以委托可访问的方式定义MyString变量，因此它还不完美。
答案 8 :(得分：3)
我的开源库Regextra支持命名格式（以及其他内容）。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: helping you reduce your (problems){2}。
指定的格式位支持：
示例：
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：
我们刚刚发送了您在2014年2月28日发布的“小工具”的订单。您的{credit}卡将收取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。
答案 9 :(得分：2)
检查一下：
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());
});
}
样品：
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，性能非常好。
答案 10 :(得分：1)
我怀疑这是可能的。首先想到的是你将如何访问本地变量名称？
然而，使用LINQ和Lambda表达式可能会有一些聪明的方法来执行此操作。
答案 11 :(得分：1)
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;
}
以下是如何使用它：
DateTime date = DateTime.Now;
string dateString = StringWithFormat("{Month}/{Day}/{Year}", date);
输出：2/27/2012
答案 12 :(得分：1)
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);
}
示例：
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}
答案 13 :(得分：1)
这是我做了一段时间的一个。它使用带有单个参数的Format方法扩展String。好的是它会使用标准的string.Format如果你提供一个像int这样的简单参数，但如果你使用像匿名类型这样的东西它也会工作。
使用示例：
"The {Name} family has {Children} children".Format(new { Children = 4, Name = "Smith" })
会导致“史密斯家庭有4个孩子。”
它不会像数组和索引器那样做疯狂的绑定。但它超级简单，性能卓越。
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;
}
}
}
答案 14 :(得分：0)
我实现了这是一个简单的类，它复制了String.Format的功能（除了使用类时）。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，因此NamedFormatString是为了向后兼容。
答案 15 :(得分：0)
我以与现有解决方案略有不同的方式解决了这个问题。 它完成了命名项替换的核心（不是某些人做过的反射位）。它非常快速而简单...... 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 + ":");
}
}
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！
答案 16 :(得分：0)
即使接受的答案提供了一些很好的例子，.Inject以及一些Haack示例也不会处理转义。许多人还严重依赖于在.NET Core和其他一些环境中不可用的Regex（较慢）或DataBinder.Eval。
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，逐个字符地写入StringBuilder输出。它以String扩展方法实现，可以将Dictionary<string, object>或object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，它处理无限级别的{{{escaping}}}并抛出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，所有的逻辑归结为10个主要状态 - 当状态机在支架外并且同样在支架内时，下一个字符是开放式支撑，逃逸开放式支撑，封闭支撑，逃脱封闭的支撑，或普通的角色。随着循环的进行，每个条件都会单独处理，将字符添加到输出StringBuffer或键StringBuffer。当参数关闭时，键StringBuffer的值用于在字典中查找参数值，然后将其推入输出StringBuffer。最后，返回输出StringBuffer的值。
答案 17 :(得分：-6)
string language = "Python";
int numquotes = 2;
string output = language + " has "+ numquotes + " language types.";
编辑： 我应该说的是，“不，我不相信你想做的事情是由C＃支持的。这就像你将得到的那样接近。”