[Solved] How can I get the Name of the Program associated with a file extension using C#? [closed]

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Use WinApi function AssocQueryString 

[DllImport("Shlwapi.dll", CharSet = CharSet.Unicode)]
public static extern uint AssocQueryString(AssocF flags, AssocStr str,
  string pszAssoc, string pszExtra, [Out]StringBuilder pszOut, ref uint pcchOut);

Create enumerations AssocF and AssocStr.

 public enum AssocStr {
        ASSOCSTR_COMMAND = 1,
        ASSOCSTR_EXECUTABLE,
        ASSOCSTR_FRIENDLYDOCNAME,
        ASSOCSTR_FRIENDLYAPPNAME,
        ASSOCSTR_NOOPEN,
        ASSOCSTR_SHELLNEWVALUE,
        ASSOCSTR_DDECOMMAND,
        ASSOCSTR_DDEIFEXEC,
        ASSOCSTR_DDEAPPLICATION,
        ASSOCSTR_DDETOPIC,
        ASSOCSTR_INFOTIP,
        ASSOCSTR_QUICKTIP,
        ASSOCSTR_TILEINFO,
        ASSOCSTR_CONTENTTYPE,
        ASSOCSTR_DEFAULTICON,
        ASSOCSTR_SHELLEXTENSION,
        ASSOCSTR_DROPTARGET,
        ASSOCSTR_DELEGATEEXECUTE,
        ASSOCSTR_SUPPORTED_URI_PROTOCOLS,
        ASSOCSTR_MAX
    }
    public enum AssocF
    {
        ASSOCF_NONE = 0x00000000,
        ASSOCF_INIT_NOREMAPCLSID = 0x00000001,
        ASSOCF_INIT_BYEXENAME = 0x00000002,
        ASSOCF_OPEN_BYEXENAME = 0x00000002,
        ASSOCF_INIT_DEFAULTTOSTAR = 0x00000004,
        ASSOCF_INIT_DEFAULTTOFOLDER = 0x00000008,
        ASSOCF_NOUSERSETTINGS = 0x00000010,
        ASSOCF_NOTRUNCATE = 0x00000020,
        ASSOCF_VERIFY = 0x00000040,
        ASSOCF_REMAPRUNDLL = 0x00000080,
        ASSOCF_NOFIXUPS = 0x00000100,
        ASSOCF_IGNOREBASECLASS = 0x00000200,
        ASSOCF_INIT_IGNOREUNKNOWN = 0x00000400,
        ASSOCF_INIT_FIXED_PROGID = 0x00000800,
        ASSOCF_IS_PROTOCOL = 0x00001000,
        ASSOCF_INIT_FOR_FILE = 0x00002000
    }

Create a helper method

static string AssocQueryString(AssocStr association, string extension) {
     const int S_OK = 0;
     const int S_FALSE = 1;

     uint length = 0;
     uint ret = AssocQueryString(AssocF.ASSOCF_NONE, association, extension, null, null, ref length);
     if (ret != S_FALSE) {
         throw new InvalidOperationException("Could not determine associated string");
     }

     var sb = new StringBuilder((int)length);
     ret = AssocQueryString(AssocF.ASSOCF_NONE, association, extension, null, sb, ref length);
     if (ret != S_OK) {
        throw new InvalidOperationException("Could not determine associated string");
     }

     return sb.ToString();

}

You can use this way

 static void Main(string[] args) {
           Console.WriteLine(AssocQueryString(AssocStr.ASSOCSTR_FRIENDLYAPPNAME, ".pdf"));
            Console.Read();
 }

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solved How can I get the Name of the Program associated with a file extension using C#? [closed]