named String.Format, is it possible?

问题

Instead of using {0} {1}, etc. I want to use {title} instead. Then fill that data in somehow (below I used a Dictionary). This code is invalid and throws an exception. I wanted to know if i can do something similar to what i want. Using {0 .. N} is not a problem. I was just curious.

Dictionary<string, string> d = new Dictionary<string, string>();
d["a"] = "he";
d["ba"] = "llo";
d["lol"] = "world";
string a = string.Format("{a}{ba}{lol}", d);

回答1:

No, but this extension method will do it

static string FormatFromDictionary(this string formatString, Dictionary<string, string> ValueDict) 
{
    int i = 0;
    StringBuilder newFormatString = new StringBuilder(formatString);
    Dictionary<string, int> keyToInt = new Dictionary<string,int>();
    foreach (var tuple in ValueDict)
    {
        newFormatString = newFormatString.Replace("{" + tuple.Key + "}", "{" + i.ToString() + "}");
        keyToInt.Add(tuple.Key, i);
        i++;                    
    }
    return String.Format(newFormatString.ToString(), ValueDict.OrderBy(x => keyToInt[x.Key]).Select(x => x.Value).ToArray());
}

回答2:

Check this one, it supports formating:

    public static string StringFormat(string format, IDictionary<string, object> values)
    {
        var matches = Regex.Matches(format, @"\{(.+?)\}");
        List<string> words = (from Match matche in matches select matche.Groups[1].Value).ToList();

        return words.Aggregate(
            format,
            (current, key) =>
                {
                    int colonIndex = key.IndexOf(':');
                    return current.Replace(
                        "{" + key + "}",
                        colonIndex > 0
                            ? string.Format("{0:" + key.Substring(colonIndex + 1) + "}", values[key.Substring(0, colonIndex)])
                            : values[key].ToString());
                });
    }

How to use:

string format = "{foo} is a {bar} is a {baz} is a {qux:#.#} is a really big {fizzle}";
var dictionary = new Dictionary<string, object>
    {
        { "foo", 123 },
        { "bar", true },
        { "baz", "this is a test" },
        { "qux", 123.45 },
        { "fizzle", DateTime.Now }
    };
StringFormat(format, dictionary)

回答3:

It's possible now

With Interpolated Strings of C# 6.0 you can do this:

string name = "John";
string message = $"Hi {name}!";
//"Hi John!"

回答4:

You can implement your own:

public static string StringFormat(string format, IDictionary<string, string> values)
{
    foreach(var p in values)
        format = format.Replace("{" + p.Key + "}", p.Value);
    return format;
}

回答5:

Phil Haack discussed several methods of doing this on his blog a while back: http://haacked.com/archive/2009/01/14/named-formats-redux.aspx. I've used the "Hanselformat" version on two projects with no complaints.

回答6:

static public class StringFormat
{
    static private char[] separator = new char[] { ':' };
    static private Regex findParameters = new Regex(
        "\\{(?<param>.*?)\\}",
        RegexOptions.Compiled | RegexOptions.Singleline);

    static string FormatNamed(
        this string format,
        Dictionary<string, object> args)
    {
        return findParameters.Replace(
            format,
            delegate(Match match)
            {
                string[] param = match.Groups["param"].Value.Split(separator, 2);

                object value;
                if (!args.TryGetValue(param[0], out value))
                    value = match.Value;

                if ((param.Length == 2) && (param[1].Length != 0))
                    return string.Format(
                        CultureInfo.CurrentCulture,
                        "{0:" + param[1] + "}",
                        value);
                else
                    return value.ToString();
            });
    }
}

A little more involved than the other extension method, but this should also allow non-string values and formatting patterns used on them, so in your original example:

Dictionary<string, object> d = new Dictionary<string, object>();
d["a"] = DateTime.Now;
string a = string.FormatNamed("{a:yyyyMMdd-HHmmss}", d);

Will also work...

回答7:

Since C# 6 released you are able to use String Interpolation feature

Code that solves your question:

string a = $"{d["a"]}{d["ba"]}{d["lol"]}";

回答8:

Why a Dictionary? It's unnecessary and overly complicated. A simple 2 dimensional array of name/value pairs would work just as well:

public static string Format(this string formatString, string[,] nameValuePairs)
{
    if (nameValuePairs.GetLength(1) != 2)
    {
        throw new ArgumentException("Name value pairs array must be [N,2]", nameof(nameValuePairs));
    }
    StringBuilder newFormat = new StringBuilder(formatString);
    int count = nameValuePairs.GetLength(0);
    object[] values = new object[count];
    for (var index = 0; index < count; index++)
    {
        newFormat = newFormat.Replace(string.Concat("{", nameValuePairs[index,0], "}"), string.Concat("{", index.ToString(), "}"));
        values[index] = nameValuePairs[index,1];
    }
    return string.Format(newFormat.ToString(), values);
}

Call the above with:

string format = "{foo} = {bar} (really, it's {bar})";
string formatted = format.Format(new[,] { { "foo", "Dictionary" }, { "bar", "unnecessary" } });

Results in: "Dictionary = unnecessary (really, it's unnecessary)"

回答9:

Here is a nice solution that is very useful when formatting emails: http://www.c-sharpcorner.com/UploadFile/e4ff85/string-replacement-with-named-string-placeholders/

Edited:

public static class StringExtension  
{  
    public static string Format( this string str, params Expression<Func<string,object>>[] args)  
    {  
        var parameters = args.ToDictionary( e=>string.Format("{{{0}}}",e.Parameters[0].Name), e=>e.Compile()(e.Parameters[0].Name));  

        var sb = new StringBuilder(str);  
        foreach(var kv in parameters)  
        {  
            sb.Replace( kv.Key, kv.Value != null ? kv.Value.ToString() : "");  
        }  

        return sb.ToString();  
    }  
}

Example usage:

public string PopulateString(string emailBody)  
{  
  User person = _db.GetCurrentUser();  
  string firstName = person.FirstName;    //  Peter  
  string lastName = person.LastName;      //  Pan  
  return StringExtension.Format(emailBody.Format(  
    firstname => firstName,  
    lastname => lastName  
  ));   
} 

回答10:

(your Dictionary + foreach + string.Replace) wrapped in a sub-routine or extension method?

Obviously unoptimized, but...

来源：https://stackoverflow.com/questions/1010123/named-string-format-is-it-possible