Creating Accessible UI components in Delphi
accessibility, delphi, delphi-2006, delphi-xe3, msaa
Solution
I was able to get this working via
unit mainAcc;
interface
uses
Winapi.Windows,
Winapi.Messages,
System.SysUtils,
System.Variants,
System.Classes,
Vcl.Graphics,
Vcl.Controls,
Vcl.Forms,
Vcl.Dialogs,
Vcl.StdCtrls,
Vcl.ComCtrls,
Vcl.ExtCtrls,
oleacc;
type
TForm1 = class(TForm)
lblFirstName: TLabel;
btnGetAccInfo: TButton;
accInfoOutput: TEdit;
procedure btnGetAccInfoClick(Sender: TObject);
procedure FormCreate(Sender: TObject);
procedure FormClose(Sender: TObject; var Action: TCloseAction);
private
{ Private declarations }
aEdit: TTWEdit;
FAccProperties: TStringList;
public
{ Public declarations }
end;
TAccessibleEdit = class(TEdit, IAccessible)
private
FOwner: TComponent;
FAccessibleItem: IAccessible;
FAccessibleName: string;
FAccessibleDescription: string;
procedure WMGetMSAAObject(var Message : TMessage); message WM_GETOBJECT;
// IAccessible
function Get_accParent(out ppdispParent: IDispatch): HResult; stdcall;
function Get_accChildCount(out pcountChildren: Integer): HResult; stdcall;
function Get_accChild(varChild: OleVariant; out ppdispChild: IDispatch): HResult; stdcall;
function Get_accName(varChild: OleVariant; out pszName: WideString): HResult; stdcall;
function Get_accValue(varChild: OleVariant; out pszValue: WideString): HResult; stdcall;
function Get_accDescription(varChild: OleVariant; out pszDescription: WideString): HResult; stdcall;
function Get_accRole(varChild: OleVariant; out pvarRole: OleVariant): HResult; stdcall;
function Get_accState(varChild: OleVariant; out pvarState: OleVariant): HResult; stdcall;
function Get_accHelp(varChild: OleVariant; out pszHelp: WideString): HResult; stdcall;
function Get_accHelpTopic(out pszHelpFile: WideString; varChild: OleVariant;
out pidTopic: Integer): HResult; stdcall;
function Get_accKeyboardShortcut(varChild: OleVariant; out pszKeyboardShortcut: WideString): HResult; stdcall;
function Get_accFocus(out pvarChild: OleVariant): HResult; stdcall;
function Get_accSelection(out pvarChildren: OleVariant): HResult; stdcall;
function Get_accDefaultAction(varChild: OleVariant; out pszDefaultAction: WideString): HResult; stdcall;
function accSelect(flagsSelect: Integer; varChild: OleVariant): HResult; stdcall;
function accLocation(out pxLeft: Integer; out pyTop: Integer; out pcxWidth: Integer;
out pcyHeight: Integer; varChild: OleVariant): HResult; stdcall;
function accNavigate(navDir: Integer; varStart: OleVariant; out pvarEndUpAt: OleVariant): HResult; stdcall;
function accHitTest(xLeft: Integer; yTop: Integer; out pvarChild: OleVariant): HResult; stdcall;
function accDoDefaultAction(varChild: OleVariant): HResult; stdcall;
function Set_accName(varChild: OleVariant; const pszName: WideString): HResult; stdcall;
function Set_accValue(varChild: OleVariant; const pszValue: WideString): HResult; stdcall;
protected
function QueryInterface(const IID: TGUID; out Obj): HResult; override;
public
constructor Create(AOwner: TComponent); override;
published
property AccessibleItem: IAccessible read FAccessibleItem write FAccessibleItem;
property AccessibleName: string read FAccessibleName write FAccessibleName;
property AccessibleDescription: string read FAccessibleDescription write FAccessibleDescription;
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
{------------------------------------------------------------------------------}
procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
inherited;
FreeAndNil(aEdit);
end;
{------------------------------------------------------------------------------}
procedure TForm1.FormCreate(Sender: TObject);
begin
aEdit := TAccessibleEdit.Create(self);
aEdit.Visible := true;
aEdit.Parent := Form1;
aEdit.Left := 91;
aEdit.Top := 17;
aEdit.Height := 21;
aEdit.Width := 204;
aEdit.Hint := 'This is a custom accessible edit control hint';
end;
{------------------------------------------------------------------------------}
procedure TForm1.btnGetAccInfoClick(Sender: TObject);
var
vWSTemp: WideString;
vAccObj: IAccessible;
begin
FAccProperties := TStringList.Create;
if (AccessibleObjectFromWindow(aEdit.Handle, OBJID_CLIENT, IID_IAccessible, vAccObj) = S_OK) then
begin
vAccObj.Get_accName(CHILDID_SELF, vWSTemp);
FAccProperties.Add('Name: ' + vWSTemp);
vWSTemp := '';
vAccObj.Get_accDescription(CHILDID_SELF, vWSTemp);
FAccProperties.Add('Description: ' + vWSTemp);
vWSTemp := '';
vAccObj.Get_accValue(CHILDID_SELF, vWSTemp);
FAccProperties.Add('Value: ' + vWSTemp);
end;
accInfoOutput.Text := FAccProperties.Text;
end;
{ TAccessibleEdit }
{------------------------------------------------------------------------------}
constructor TAccessibleEdit.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
FOwner := AOwner;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.QueryInterface(const IID: TGUID; out Obj): HResult;
begin
if GetInterface(IID, Obj) then
Result := 0
else
Result := E_NOINTERFACE;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.accDoDefaultAction(varChild: OleVariant): HResult;
begin
Result := DISP_E_MEMBERNOTFOUND;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.accHitTest(xLeft, yTop: Integer;
out pvarChild: OleVariant): HResult;
begin
Result := DISP_E_MEMBERNOTFOUND;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.accLocation(out pxLeft, pyTop, pcxWidth, pcyHeight: Integer;
varChild: OleVariant): HResult;
var
P: TPoint;
begin
Result := S_FALSE;
pxLeft := 0;
pyTop := 0;
pcxWidth := 0;
pcyHeight := 0;
if varChild = CHILDID_SELF then
begin
P := self.ClientToScreen(self.ClientRect.TopLeft);
pxLeft := P.X;
pyTop := P.Y;
pcxWidth := self.Width;
pcyHeight := self.Height;
Result := S_OK;
end
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.accNavigate(navDir: Integer; varStart: OleVariant;
out pvarEndUpAt: OleVariant): HResult;
begin
result := DISP_E_MEMBERNOTFOUND;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.accSelect(flagsSelect: Integer; varChild: OleVariant): HResult;
begin
Result := DISP_E_MEMBERNOTFOUND;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accChild(varChild: OleVariant;
out ppdispChild: IDispatch): HResult;
begin
Result := DISP_E_MEMBERNOTFOUND;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accChildCount(out pcountChildren: Integer): HResult;
begin
Result := DISP_E_MEMBERNOTFOUND;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accDefaultAction(varChild: OleVariant;
out pszDefaultAction: WideString): HResult;
begin
Result := DISP_E_MEMBERNOTFOUND;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accDescription(varChild: OleVariant;
out pszDescription: WideString): HResult;
begin
pszDescription := '';
result := S_FALSE;
if varChild = CHILDID_SELF then
begin
pszDescription := 'TAccessibleEdit_AccessibleDescription';
Result := S_OK;
end;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accFocus(out pvarChild: OleVariant): HResult;
begin
Result := DISP_E_MEMBERNOTFOUND;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accHelp(varChild: OleVariant;
out pszHelp: WideString): HResult;
begin
Result := DISP_E_MEMBERNOTFOUND;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accHelpTopic(out pszHelpFile: WideString;
varChild: OleVariant; out pidTopic: Integer): HResult;
begin
pszHelpFile := '';
pidTopic := 0;
Result := S_FALSE;
if varChild = CHILDID_SELF then
begin
pszHelpFile := '';
pidTopic := self.HelpContext;
Result := S_OK;
end;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accKeyboardShortcut(varChild: OleVariant;
out pszKeyboardShortcut: WideString): HResult;
begin
Result := DISP_E_MEMBERNOTFOUND;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accName(varChild: OleVariant; out pszName: WideString): HResult;
begin
pszName := '';
Result := S_FALSE;
if varChild = CHILDID_SELF then
begin
pszName := 'TAccessibleEdit_AccessibleName';
result := S_OK;
end;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accParent(out ppdispParent: IDispatch): HResult;
begin
ppdispParent := nil;
result := AccessibleObjectFromWindow(self.ParentWindow, CHILDID_SELF, IID_IAccessible, Pointer(ppDispParent));
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accRole(varChild: OleVariant;
out pvarRole: OleVariant): HResult;
begin
Result := S_OK;
if varChild = CHILDID_SELF then
pvarRole := ROLE_SYSTEM_OUTLINE;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accSelection(out pvarChildren: OleVariant): HResult;
begin
Result := DISP_E_MEMBERNOTFOUND;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accState(varChild: OleVariant;
out pvarState: OleVariant): HResult;
begin
Result := S_OK;
if varChild = CHILDID_SELF then
pvarState := STATE_SYSTEM_FOCUSED;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Get_accValue(varChild: OleVariant;
out pszValue: WideString): HResult;
begin
pszValue := '';
Result := S_FALSE;
if varChild = CHILDID_SELF then
begin
pszValue := WideString(self.Text);
result := S_OK;
end;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Set_accName(varChild: OleVariant;
const pszName: WideString): HResult;
begin
Result := DISP_E_MEMBERNOTFOUND;
end;
{------------------------------------------------------------------------------}
function TAccessibleEdit.Set_accValue(varChild: OleVariant;
const pszValue: WideString): HResult;
begin
Result := DISP_E_MEMBERNOTFOUND;
end;
{------------------------------------------------------------------------------}
procedure TAccessibleEdit.WMGetMSAAObject(var Message : TMessage);
begin
if (Message.Msg = WM_GETOBJECT) then
begin
QueryInterface(IID_IAccessible, FAccessibleItem);
Message.Result := LresultFromObject(IID_IAccessible, Message.WParam, FAccessibleItem);
end
else
Message.Result := DefWindowProc(Handle, Message.Msg, Message.WParam, Message.LParam);
end;
end.
end.
Problem
I am trying to retrieve accessible information from a standard VCL TEdit control. The get_accName() and Get_accDescription() methods return empty strings, but get_accValue() returns the text value entered into the TEdit. I am just starting to try to understand the MSAA and I'm a bit lost at this point. Does my TEdit need to have additional published properties that would be exposed to the MSA? If so would that necessitate creating a new component that descends from TEdit and adds the additional published properties such as "AccessibleName", "AccessibleDescription", etc... ? Also, note, I have looked at the VTVirtualTrees component which is supposed to be accessible, but the MS Active Accessibility Object Inspector still does not see the AccessibleName published property even on that control. At this point I am at a loss and would be grateful for any advice or help in this matter. ``` ... interface uses Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.ComCtrls, Vcl.ExtCtrls, oleacc; const WM_GETOBJECT = $003D; // Windows MSAA message identifier OBJID_NATIVEOM = $FFFFFFF0; type TForm1 = class(TForm) lblFirstName: TLabel; edFirstName: TEdit; panel1: TPanel; btnGetAccInfo: TButton; accInfoOutput: TEdit; procedure btnGetAccInfoClick(Sender: TObject); procedure edFirstNameChange(Sender: TObject); private { Private declarations } FFocusedAccessibleObj: IAccessible; FvtChild: Variant; FAccProperties: TStringList; FAccName: string; FAccDesc: string; FAccValue: string; procedure DoGetAccessibleObjectFromPoint(aPoint: TPoint); public { Public declarations } procedure BeforeDestruction; override; property AccName: string read FAccName; property AccDescription: string read FAccName; property AccValue: string read FAccName; end; var Form1: TForm1; const cCRLF = #13#10; implementation {$R *.dfm} function AccessibleObjectFromPoint(ptScreen: TPoint; out ppacc: IAccessible; out pvarChildt: Variant): HRESULT; stdcall; external 'oleacc.dll' ; {------------------------------------------------------------------------------} procedure TForm1.BeforeDestruction; begin VarClear(FvtChild); FFocusedAccessibleObj := nil; end; {------------------------------------------------------------------------------} procedure TForm1.DoGetAccessibleObjectFromPoint(aPoint: TPoint); var pt: TPoint; bsName: WideString; bsDesc: WideString; bsValue: WideString; begin if (SUCCEEDED(AccessibleObjectFromPoint(aPoint, FFocusedAccessibleObj, FvtChild))) then try // get_accName returns an empty string bsName := ''; FFocusedAccessibleObj.get_accName(FvtChild, bsName); FAccName := bsName; FAccProperties.Add('Acc Name: ' + FAccName + ' | ' + cCRLF); // Get_accDescription returns an empty string bsDesc := ''; FFocusedAccessibleObj.Get_accDescription(FvtChild, bsDesc); FAccDesc := bsDesc; FAccProperties.Add('Acc Description: ' + FAccDesc + ' | ' + cCRLF); // this works bsValue := ''; FFocusedAccessibleObj.get_accValue(FvtChild, bsValue); FAccValue := bsValue; FAccProperties.Add('Acc Value: ' + FAccValue + cCRLF); finally VarClear(FvtChild); FFocusedAccessibleObj := nil ; end; end; {------------------------------------------------------------------------------} procedure TForm1.btnGetAccInfoClick(Sender: TObject); begin FAccProperties := TStringList.Create; DoGetAccessibleObjectFromPoint(edFirstName.ClientOrigin); accInfoOutput.Text := FAccProperties.Text; end; end. ```