Getting the associated icon of a file extension

This article introduces a function you can use to get the associated icon of a file or document based on its file extension (i.e. it doesn't matter if the file or document exists on disk or not)

ExtractAssociatedIcon

To get the icon of an application or document we can use this API function (declared in the ShellAPI unit):



function ExtractAssociatedIcon(hInst: HINST; lpIconPath: PChar;

  var lpiIcon: Word): HICON; stdcall;


hInst: The application handle. This value is contained in the predefined variable HInstance.



lpIconPath: A pointer to a character buffer that should contain a null terminated string with the full path name of the application, library (DLL) or document. If it is a document, the function will place there the full pathname of the associated application from where the icon was extracted, so we should allocate a buffer large enough.



lpiIcon: The icon index (the first icon in the file has an index of 0). If lpIconPath specifies a document, then lpiIcon is set by the function (that's why it is passed by reference) to the index position of the actual icon taken from the associated executable (defined in the file association).



Return value: If the function fails, it returns 0. If it succeeds, it returns an icon handle, which is an integer value Windows uses to identify the allocated resource. It is not necessary to call the API DestroyIcon to release the icon since it'll be deallocated automatically when the application finishes, although you can do it if you want.



SAMPLE CALL

Now, what do we do with the icon handle? Normally what we want is an icon, namely and instance of the TIcon class. All we have to do is create a TIcon object and assign this handle to its Handle property. If later we assign the Handle property to another value, the previous icon will be automatically be released. The same happens if the TIcon object is freed.



Here is an example that changes the icon of the form:



uses SysUtils, Windows, ShellAPI;



  procedure TForm1.Button1Click(Sender: TObject);

  var

    IconIndex: word;

    Buffer: array[0..2048] of char;

    IconHandle: HIcon;

  begin

    StrCopy(@Buffer, 'C:\Windows\Help\Windows.hlp');

    IconIndex := 0;

    IconHandle := ExtractAssociatedIcon(HInstance, Buffer, IconIndex);

    if IconHandle <> 0 then

      Icon.Handle := IconHandle;

  end;


GETASSOCIATEDICON

Unfortunately, ExtractAssociatedIcon fails if the file does not exist on disk, so we defined a procedure that gets the icon of a file whether it exists or not, and can also get the small icon (ideal for a TListView that can be shown in vsIcon or vsReport view styles). The procedure receives three parameters: the filename and two pointers to HICON (integer) variables: one for the large icon (32x32) and another one for the small icon (16x16). Any of them can be nil if you don't need one of these icons. The icons "returned" by the procedure must be freed with the DestroyIcon API. This will be done automatically if you assign the icon handle (HICON) to the Handle property of a TIcon object (the icon will be released when this object gets freed or a new value is assigned to it).



uses SysUtils, Registry, Windows, ShellAPI;



  type

    PHICON = ^HICON;



  procedure GetAssociatedIcon(FileName: TFilename;

      PLargeIcon, PSmallIcon: PHICON);

  // Gets the icons of a given file

  var

    IconIndex: word; // Position of the icon in the file

    FileExt, FileType: string;

    Reg: TRegistry;

    p: integer;

    p1, p2: pchar;

  label

    noassoc;

  begin

    IconIndex := 0;

    // Get the extension of the file

    FileExt := UpperCase(ExtractFileExt(FileName));

    if ((FileExt <> '.EXE') and (FileExt <> '.ICO')) or

        not FileExists(FileName) then begin

      // If the file is an EXE or ICO and it exists, then

      // we will extract the icon from this file. Otherwise

      // here we will try to find the associated icon in the

      // Windows Registry...

      Reg := nil;

      try

        Reg := TRegistry.Create(KEY_QUERY_VALUE);

        Reg.RootKey := HKEY_CLASSES_ROOT;

        if FileExt = '.EXE' then FileExt := '.COM';

        if Reg.OpenKeyReadOnly(FileExt) then

          try

            FileType := Reg.ReadString('');

          finally


            Reg.CloseKey;

          end;

        if (FileType <> '') and Reg.OpenKeyReadOnly(

            FileType + '\DefaultIcon') then

          try

            FileName := Reg.ReadString('');

          finally

            Reg.CloseKey;

          end;

      finally

        Reg.Free;

      end;



      // If we couldn't find the association, we will

      // try to get the default icons

      if FileName = '' then goto noassoc;



      // Get the filename and icon index from the

      // association (of form '"filaname",index')

      p1 := PChar(FileName);

      p2 := StrRScan(p1, ',');

      if p2 <> nil then begin

        p := p2 - p1 + 1; // Position of the comma

        IconIndex := StrToInt(Copy(FileName, p + 1,

          Length(FileName) - p));

        SetLength(FileName, p - 1);

      end;

    end;

    // Attempt to get the icon

    if ExtractIconEx(pchar(FileName), IconIndex,

        PLargeIcon^, PSmallIcon^, 1) <> 1 then

    begin

noassoc:

      // The operation failed or the file had no associated

      // icon. Try to get the default icons from SHELL32.DLL



      try // to get the location of SHELL32.DLL

        FileName := IncludeTrailingBackslash(GetSystemDir)

          + 'SHELL32.DLL';

      except

        FileName := 'C:\WINDOWS\SYSTEM\SHELL32.DLL';

      end;

      // Determine the default icon for the file extension

      if (FileExt = '.DOC') then IconIndex := 1

      else if (FileExt = '.EXE')

           or (FileExt = '.COM') then IconIndex := 2

      else if (FileExt = '.HLP') then IconIndex := 23

      else if (FileExt = '.INI')

           or (FileExt = '.INF') then IconIndex := 63

      else if (FileExt = '.TXT') then IconIndex := 64

      else if (FileExt = '.BAT') then IconIndex := 65

      else if (FileExt = '.DLL')

           or (FileExt = '.SYS')

           or (FileExt = '.VBX')

           or (FileExt = '.OCX')

           or (FileExt = '.VXD') then IconIndex := 66

      else if (FileExt = '.FON') then IconIndex := 67

      else if (FileExt = '.TTF') then IconIndex := 68

      else if (FileExt = '.FOT') then IconIndex := 69

      else IconIndex := 0;

      // Attempt to get the icon.

      if ExtractIconEx(pchar(FileName), IconIndex,

          PLargeIcon^, PSmallIcon^, 1) <> 1 then

      begin

        // Failed to get the icon. Just "return" zeroes.

        if PLargeIcon <> nil then PLargeIcon^ := 0;

        if PSmallIcon <> nil then PSmallIcon^ := 0;

      end;

    end;

  end;


SAMPLE CALL

This example will change the icon of your form:



procedure TForm1.Button1Click(Sender: TObject);

  var

    SmallIcon: HICON;

  begin

    GetAssociatedIcon('file.doc', nil, @SmallIcon);

    if SmallIcon <> 0 then

      Icon.Handle := SmallIcon;

  end;

 

Share this article!

Follow us!

Find more helpful articles: