Getting a ReadOnly Published property in Delphi using RTTI without exceptions

Question

I want to use RTTI to determine if a control is read-only. My code currently looks like this and works fine.

function ControlIsReadOnly(const Control: TControl): Boolean;
var
  Value: Variant;
begin
  try
    Value := GetPropValue(Control, 'ReadOnly');
    Result := Value;
  except
    Result := False;
  end;
end;

Is there a nice way to do this without raising an exception if the property is absent?

Answer 1

You can use GetPropInfo(), which returns a pointer to a TPropInfo if the property is found, or nil if not found. GetPropValue() (and other getter functions) has an overload which takes a TPropInfo pointer, eg:

function ControlIsReadOnly(const Control: TControl): Boolean;
var
  PropInfo: PPropInfo;
begin
  PropInfo := GetPropInfo(Control, 'ReadOnly');
  if PropInfo <> nil then
    Result := GetPropValue(Control, PropInfo)
    // or: 
    // Result := Boolean(GetOrdProp(Control, PropInfo))
  else
    Result := False;
end;