IAccessible: How Get value of url bar in Mozilla Firefox?

Question

I'm working in a code that promise get value from url bar, but now appear one compilation error in some parameters of IAccessible get_accValue property. So, how fix?

Any help will be appreciated!

Here is the my code:

uses
  oleacc;

function ffdoc: THandle;
const
  A_szClassName: array[0..6] of PChar = ('MozillaUIWindowClass','MozillaWindowClass',
  'MozillaWindowClass','MozillaWindowClass','MozillaContentWindowClass',
  'MozillaWindowClass','MozillaWindowClass');
var
  i: Integer;
begin
  Result:= 0;
  for i:= 0 to 6 do
    Result:= FindWindowEx(Result,THandle(nil),A_szClassName[i],nil);
end;

function ffurl:string;
var
  acc: IAccessible;
  pw: PWChar;
begin
  if AccessibleObjectFromWindow(ffdoc,OBJID_CLIENT,IID_IAccessible,Pointer(acc)) = 0 then
    Acc.get_accValue(CHILDID_SELF,pw);
  Result:= pw;
end;

Answer 1

If you look at the declaration for oleacc.IAccessible.get_accValue(), it is apparent why you are getting the error:

function Get_accValue(varChild: OleVariant; out pszValue: WideString): HResult; stdcall;

You are trying to pass a PWChar where an out WideString is expected. Delphi is very strict when it comes to var and out parameters.

You need to change your pw variable:

function ffurl:string;
var
  acc: IAccessible;
  pw: WideString;
begin
  if AccessibleObjectFromWindow(ffdoc, OBJID_CLIENT, IID_IAccessible, acc) = 0 then
    acc.get_accValue(CHILDID_SELF, pw);
  Result := pw;
end;

COM uses BSTR for its strings, which Delphi wraps with WideString. So always use WideString when passing strings in/out of COM interfaces.