Autocompletion for TEdits revisited

I wrote about autocompletion for TEdits before here and here.

Back then I was using the SHAutoComplete API function in the Shlwapi.dll because I am a lazy basterd™. That hasn’t changed really but I also love fiddling with stuff, so some years ago, I actually added directory and general string completion to dzlib (and apparently didn’t blog about it), this time using the IAutoComplete2 interface as described in this answer on StackOverflow, which I mentioned before.

Today I revisited that code and and added file and directory completion to it, in a way that also allows filtering the files with a given file mask. So the user can easily enter directories and eventually select a file:

To add this functionality to a TEdit control, one only needs to add the unit u_dzAutoCompleteFiles to the form and call TEdit_ActivateAutoCompleteFiles in the form’s constructor like this:

constructor Tf_AutoCompleteTest.Create(_Owner: TComponent);
begin
  inherited;
  TEdit_ActivateAutoCompleteFiles(ed_AutoCompleteFiles, '*.dfm');
end;

The magic happens in a helper class TEnumStringFiles derived from the same TEnumStringAbstract class as TEnumStringDirs and TEnumStringStringList, implementing the IEnumString interface. It implements three methods:

• function Next(celt: LongInt; out elt; pceltFetched: PLongInt): HResult;
• function Reset: HResult
• function Skip(celt:LongInt): HResult;

Reset is called whenever Windows thinks it needs to get the autocompletion list. Basically that’s whenever the user presses the backslash key, but apparently there are also other events that trigger it. After that the functions Next and possibly Skip are called to get the actual list.

Since this class is supposed to return directories and files, it uses two instances of TSimpleDirectoryEnum which encapsulates SysUtils.FindFirst and SysUtils.FindNext. One is for directories the other is for files matching a given mask (actually “mask” is not quite the right word as the “mask” is always appended to the base string the user has entered).

Here is the complete unit (but you should really get the code from Sourceforge to make sure the get the latest version):

unit u_dzAutoCompleteFiles;

interface

uses
  Windows,
  Messages,
  SysUtils,
  Classes,
  StdCtrls,
  ActiveX,
  u_dzfileutils,
  i_dzAutoComplete;

type
  TOnGetBaseFileEvent = procedure(_Sender: TObject; out _Base: string) of object;

type
  ///<summary>
  /// Implementaition of IEnumString for files </summary>
  TEnumStringFiles = class(TEnumStringAbstract, IEnumString)
  private
    FOnGetBase: TOnGetBaseFileEvent;
    FDirEnum: TSimpleDirEnumerator;
    FFileEnum: TSimpleDirEnumerator;
    FBase: string;
    FFilter: string;
    procedure doOnGetBase(out _Base: string);
    function FindNextDirOrFile(out _DirOrFilename: WideString): Boolean;
  protected
    // IEnumString
    function Next(celt: Longint; out elt;
      pceltFetched: PLongint): HResult; override;
    function Skip(celt: Longint): HResult; override;
    function Reset: HResult; override;
  public
    constructor Create(_OnGetBase: TOnGetBaseFileEvent; const _Filter: string);
    destructor Destroy; override;
  end;

procedure TEdit_ActivateAutoCompleteFiles(_ed: TCustomEdit; const _Filter: string);

implementation

{ TEnumStringFiles }

constructor TEnumStringFiles.Create(_OnGetBase: TOnGetBaseFileEvent; const _Filter: string);
begin
  inherited Create;
  FFilter := _Filter;
  FOnGetBase := _OnGetBase;
end;

destructor TEnumStringFiles.Destroy;
begin
  FreeAndNil(FDirEnum);
  FreeAndNil(FFileEnum);
  inherited;
end;

procedure TEnumStringFiles.doOnGetBase(out _Base: string);
begin
  if Assigned(FOnGetBase) then
    FOnGetBase(Self, _Base);
end;

function TEnumStringFiles.FindNextDirOrFile(out _DirOrFilename: WideString): Boolean;
var
  fn: string;
begin
  if Assigned(FDirEnum) then begin
    Result := FDirEnum.FindNext(fn, True);
    if Result then begin
      _DirOrFilename := fn;
      Exit; //==>
    end;
  end;

  if Assigned(FFileEnum) then begin
    Result := FFileEnum.FindNext(fn, True);
    if Result then begin
      _DirOrFilename := fn;
      Exit; //==>
    end;
  end;
  Result := False;
end;

function TEnumStringFiles.Next(celt: Integer; out elt; pceltFetched: PLongint): HResult;
var
  i: Integer;
  wStr: WideString;
begin
  i := 0;
  while (i < celt) and FindNextDirOrFile(wStr) do begin
    TPointerList(elt)[i] := Pointer(wStr);
    Pointer(wStr) := nil;
    Inc(i);
  end;
  if pceltFetched <> nil then
    pceltFetched^ := i;
  if i = celt then
    Result := S_OK
  else
    Result := S_FALSE;
end;

function TEnumStringFiles.Reset: HResult;
begin
  doOnGetBase(FBase);
  FreeAndNil(FDirEnum);
  FreeAndNil(FFileEnum);
  FDirEnum := TSimpleDirEnumerator.CreateForDirsOnly(FBase + '*');
  FFileEnum := TSimpleDirEnumerator.CreateForFilesOnly(FBase + FFilter);
  Result := S_OK;
end;

function TEnumStringFiles.Skip(celt: Integer): HResult;
var
  i: Integer;
  wStr: WideString;
begin
  i := 0;
  while FindNextDirOrFile(wStr) do begin
    Inc(i);
    if i < celt then begin
      Result := S_OK;
      Exit; //==>
    end;
  end;
  Result := S_FALSE;
end;

type
  TAutoCompleteHelperFiles = class(TAutoCompleteHelper)
  private
    FFilter: string;
    procedure HandleOnGetBase(_Sender: TObject; out _Base: string);
  protected
    function CreateEnumStringInt: IEnumString; override;
  public
    constructor Create(_ed: TCustomEdit; const _Filter: string);
  end;

procedure TEdit_ActivateAutoCompleteFiles(_ed: TCustomEdit; const _Filter: string);
begin
  TAutoCompleteHelperFiles.Create(_ed, _Filter);
end;

{ TAutoCompleteHelperFiles }

constructor TAutoCompleteHelperFiles.Create(_ed: TCustomEdit; const _Filter: string);
begin
  FFilter := _Filter;
  inherited Create(_ed);
end;

function TAutoCompleteHelperFiles.CreateEnumStringInt: IEnumString;
begin
  Result := TEnumStringFiles.Create(HandleOnGetBase, FFilter);
end;

procedure TAutoCompleteHelperFiles.HandleOnGetBase(_Sender: TObject; out _Base: string);
begin
  _Base := (FCtrl as TCustomEdit).Text;
end;

end.

The code is in the newly added u_dzAutoCompleteFiles unit in my dzlib.

If you would like to comment on this, go to this post in the international Delphi Praxis forum.