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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.
The VCL itself does not natively implement any support for MSAA. Windows provides default implementations for standard UI controls, which many standard VCL components wrap. If you need more MSAA support than Windows provides, you will have to implement the
IAccessibleinterface yourself, and then have your control respond to theWM_GETOBJECTmessage so it can return a pointer to an instance of your implementation.Update: For example, one way to add MSAA to an existing
TEdit(if you do not want to derive your own component) might look something like this:I was able to get this working via