MimeMapping.GetMimeMapping的對面？

Question

存在MimeMapping.GetMimeMapping(string filename)

是否存在.Net函數，即「相反」。這需要一個MIME字符串並返回文件類型擴展名？

Answer 1

您可以閱讀註冊表以獲取該信息。

var mapping = Microsoft.Win32.Registry.ClassesRoot.GetSubKeyNames() 
       .Select(key => new 
       { 
        Key = key, 
        ContentType = Microsoft.Win32.Registry.ClassesRoot.OpenSubKey(key).GetValue("Content Type") 
       }) 
       .Where(x => x.ContentType != null) 
       .ToLookup(x => x.ContentType, x => x.Key); 

Console.WriteLine(String.Join(";",mapping["image/jpeg"])); 

Answer 2

有正好碰上這個自己和不高興具有（通過提供一個備用名單什麼MimeMapping使用）GetMimeMapping和反向之間的不匹配，我挖成MimeMapping本身獲得其內部的映射。

public static IEnumerable<string> GetExtensions(this string mimeType) 
{ 
    var mappingDictionaryField = typeof(MimeMapping).GetField("_mappingDictionary", BindingFlags.NonPublic | BindingFlags.Static); 

    if (mappingDictionaryField == null) 
     return new string[0]; 

    // get the internal dictionary used for mime type lookup 
    var mappingDictionary = mappingDictionaryField.GetValue(null); 

    if (mappingDictionary == null) 
     return new string[0]; 

    // get type that owns the populate method and populated dictionary 
    var dictionaryType = mappingDictionary.GetType().BaseType; 

    if (dictionaryType == null) 
     return new string[0]; 

    var populateMethod = dictionaryType.GetMethod("PopulateMappings", BindingFlags.NonPublic | BindingFlags.Instance); 

    if (populateMethod == null) 
     return new string[0]; 

    populateMethod.Invoke(mappingDictionary, null); 

    // get the populated mapping dictionary 
    var mappingField = dictionaryType.GetField("_mappings", BindingFlags.Instance | BindingFlags.NonPublic); 

    if (mappingField == null) 
     return new string[0]; 

    var mapping = mappingField.GetValue(mappingDictionary) as IDictionary<string, string>; 

    if (mapping == null) 
     return new string[0]; 

    var extensions = mapping.Where(x => x.Value == mimeType) 
          .Select(x => x.Key); 

    return extensions; 
} 

我決定不扔在反思失敗的情況例外，只是不返回擴展，因爲它符合我個人的使用情況。