Associate your program with file extension

article source : http://www.delphi3000.com/articles/article_525.asp?SK=
author : Igor Siticov

For creating file associations you should make some registry changes and inform Windows explorer about your changes.

For launching your program as default for all unregistered file types just associate it for “*” file type.

The following unit includes realization of function for creating file association.
See comments in source for details.

unit utils;

interface
uses Registry, ShlObj, SysUtils, Windows;

procedure RegisterFileType(cMyExt, cMyFileType, cMyDescription, ExeName: string; IcoIndex: integer; DoUpdate: boolean = false);

implementation

procedure RegisterFileType(cMyExt, cMyFileType, cMyDescription, ExeName: string; IcoIndex: integer; DoUpdate: boolean = false);
var
   Reg: TRegistry;
begin
  Reg := TRegistry.Create;
  try
    Reg.RootKey := HKEY_CLASSES_ROOT;
    Reg.OpenKey(cMyExt, True);
    // Write my file type to it.
    // This adds HKEY_CLASSES_ROOT\.abc\(Default) = 'Project1.FileType'
    Reg.WriteString('', cMyFileType);
    Reg.CloseKey;
    // Now create an association for that file type
    Reg.OpenKey(cMyFileType, True);
    // This adds HKEY_CLASSES_ROOT\Project1.FileType\(Default)
    //   = 'Project1 File'
    // This is what you see in the file type description for
    // the a file's properties.
    Reg.WriteString('', cMyDescription);
    Reg.CloseKey;    // Now write the default icon for my file type
    // This adds HKEY_CLASSES_ROOT\Project1.FileType\DefaultIcon
    //  \(Default) = 'Application Dir\Project1.exe,0'
    Reg.OpenKey(cMyFileType + '\DefaultIcon', True);
    Reg.WriteString('', ExeName + ',' + IntToStr(IcoIndex));
    Reg.CloseKey;
    // Now write the open action in explorer
    Reg.OpenKey(cMyFileType + '\Shell\Open', True);
    Reg.WriteString('', '&Open');
    Reg.CloseKey;
    // Write what application to open it with
    // This adds HKEY_CLASSES_ROOT\Project1.FileType\Shell\Open\Command
    //  (Default) = '"Application Dir\Project1.exe" "%1"'
    // Your application must scan the command line parameters
    // to see what file was passed to it.
    Reg.OpenKey(cMyFileType + '\Shell\Open\Command', True);
    Reg.WriteString('', '"' + ExeName + '" "%1"');
    Reg.CloseKey;
    // Finally, we want the Windows Explorer to realize we added
    // our file type by using the SHChangeNotify API.
    if DoUpdate then SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_IDLIST, nil, nil);
  finally
    Reg.Free;
  end;
end;

end.