Post a Comment On: mo.notono.us

I generally prefer to use String.Format() instead of doing a bunch of string additions, but constantly find myself splitting the code onto multiple lines with an appended comment to keep track of the indices: string myString = string.Format("{0} is {1} and {2} is {3}", o.foo, //0 o.bar, //1 o.yadi, //2 o.yada //3 ); Wouldn't it be nice you could instead write something like this?: string myString = "{foo} is {bar} and {yadi} is {yada}".Inject(o); Well, now you can - see the string extension method Inject below; it accepts an object, IDictionary or HashTable and replaces the property name/key tokens with the instance values.  Since it uses string.Format internally, it also supports string.Format-like custom formatting: 1: using System; 2: using System.Text.RegularExpressions; 3: using System.Collections; 4: using System.Globalization; 5: using System.ComponentModel; 6:   7: [assembly: CLSCompliant(true)] 8: namespace StringInject 9: { 10: public static class StringInjectExtension 11: { 12: /// <summary> 13: /// Extension method that replaces keys in a string with the values of matching object properties. 14: /// <remarks>Uses <see cref="String.Format()"/> internally; custom formats should match those used for that method.</remarks> 15: /// </summary> 16: /// <param name="formatString">The format string, containing keys like {foo} and {foo:SomeFormat}.</param> 17: /// <param name="injectionObject">The object whose properties should be injected in the string</param> 18: /// <returns>A version of the formatString string with keys replaced by (formatted) key values.</returns> 19: public static string Inject(this string formatString, object injectionObject) 20: { 21: return formatString.Inject(GetPropertyHash(injectionObject)); 22: } 23:   24: /// <summary> 25: /// Extension method that replaces keys in a string with the values of matching dictionary entries. 26: /// <remarks>Uses <see cref="String.Format()"/> internally; custom formats should match those used for that method.</remarks> 27: /// </summary> 28: /// <param name="formatString">The format string, containing keys like {foo} and {foo:SomeFormat}.</param> 29: /// <param name="dictionary">An <see cref="IDictionary"/> with keys and values to inject into the string</param> 30: /// <returns>A version of the formatString string with dictionary keys replaced by (formatted) key values.</returns> 31: public static string Inject(this string formatString, IDictionary dictionary) 32: { 33: return formatString.Inject(new Hashtable(dictionary)); 34: } 35:   36: /// <summary> 37: /// Extension method that replaces keys in a string with the values of matching hashtable entries. 38: /// <remarks>Uses <see cref="String.Format()"/> internally; custom formats should match those used for that method.</remarks> 39: /// </summary> 40: /// <param name="formatString">The format string, containing keys like {foo} and {foo:SomeFormat}.</param> 41: /// <param name="attributes">A <see cref="Hashtable"/> with keys and values to inject into the string</param> 42: /// <returns>A version of the formatString string with hastable keys replaced by (formatted) key values.</returns> 43: public static string Inject(this string formatString, Hashtable attributes) 44: { 45: string result = formatString; 46: if (attributes == null || formatString == null) 47: return result; 48:   49: foreach (string attributeKey in attributes.Keys) 50: { 51: result = result.InjectSingleValue(attributeKey, attributes[attributeKey]); 52: } 53: return result; 54: } 55:   56: /// <summary> 57: /// Replaces all instances of a 'key' (e.g. {foo} or {foo:SomeFormat}) in a string with an optionally formatted value, and returns the result. 58: /// </summary> 59: /// <param name="formatString">The string containing the key; unformatted ({foo}), or formatted ({foo:SomeFormat})</param> 60: /// <param name="key">The key name (foo)</param> 61: /// <param name="replacementValue">The replacement value; if null is replaced with an empty string</param> 62: /// <returns>The input string with any instances of the key replaced with the replacement value</returns> 63: public static string InjectSingleValue(this string formatString, string key, object replacementValue) 64: { 65: string result = formatString; 66: //regex replacement of key with value, where the generic key format is: 67: //Regex foo = new Regex("{(foo)(?:}|(?::(.[^}]*)}))"); 68: Regex attributeRegex = new Regex("{(" + key + ")(?:}|(?::(.[^}]*)}))"); //for key = foo, matches {foo} and {foo:SomeFormat} 69: 70: //loop through matches, since each key may be used more than once (and with a different format string) 71: foreach (Match m in attributeRegex.Matches(formatString)) 72: { 73: string replacement = m.ToString(); 74: if (m.Groups[2].Length > 0) //matched {foo:SomeFormat} 75: { 76: //do a double string.Format - first to build the proper format string, and then to format the replacement value 77: string attributeFormatString = string.Format(CultureInfo.InvariantCulture, "{{0:{0}}}", m.Groups[2]); 78: replacement = string.Format(CultureInfo.CurrentCulture, attributeFormatString, replacementValue); 79: } 80: else //matched {foo} 81: { 82: replacement = (replacementValue ?? string.Empty).ToString(); 83: } 84: //perform replacements, one match at a time 85: result = result.Replace(m.ToString(), replacement); //attributeRegex.Replace(result, replacement, 1); 86: } 87: return result; 88:   89: } 90:   91:   92: /// <summary> 93: /// Creates a HashTable based on current object state. 94: /// <remarks>Copied from the MVCToolkit HtmlExtensionUtility class</remarks> 95: /// </summary> 96: /// <param name="properties">The object from which to get the properties</param> 97: /// <returns>A <see cref="Hashtable"/> containing the object instance's property names and their values</returns> 98: private static Hashtable GetPropertyHash(object properties) 99: { 100: Hashtable values = null; 101: if (properties != null) 102: { 103: values = new Hashtable(); 104: PropertyDescriptorCollection props = TypeDescriptor.GetProperties(properties); 105: foreach (PropertyDescriptor prop in props) 106: { 107: values.Add(prop.Name, prop.GetValue(properties)); 108: } 109: } 110: return values; 111: } 112:   113: } 114: } File downloads: StringInjectExtension CS file. VisualStudio 2008 project (including 14 unit tests).