Même si la réponse acceptée donne de bons exemples, le .Inject ainsi que certains des exemples Haack ne gèrent pas les échappements. Beaucoup dépendent également fortement de Regex (plus lent) ou de DataBinder.Eval qui n'est pas disponible sur .NET Core et dans certains autres environnements.
Dans cet esprit, j'ai écrit un analyseur simple basé sur une machine à états qui diffuse les caractères, en écrivant dans une StringBuildersortie, caractère par caractère. Il est implémenté en tant que Stringméthode (s) d'extension et peut prendre à la fois un Dictionary<string, object>ouobject avec des paramètres en entrée (en utilisant la réflexion).
Il gère des niveaux illimités de {{{escaping}}}et jette FormatExceptionlorsque l'entrée contient des accolades déséquilibrées et / ou d'autres erreurs.
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;
}
}
En fin de compte, toute la logique se résume en 10 états principaux - Pour lorsque la machine à états est en dehors d'un crochet et également à l'intérieur d'un crochet, le caractère suivant est soit une accolade ouverte, une accolade ouverte échappée, une accolade fermée, une accolade fermée échappée, ou un personnage ordinaire. Chacune de ces conditions est gérée individuellement à mesure que la boucle progresse, ajoutant des caractères à une sortie StringBufferou à une clé StringBuffer. Lorsqu'un paramètre est fermé, la valeur de la clé StringBufferest utilisée pour rechercher la valeur du paramètre dans le dictionnaire, qui est ensuite poussée dans la sortie StringBuffer. À la fin, la valeur de la sortie StringBufferest renvoyée.