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How to determine if an object has a particular property (Views: 100)


Problem/Question/Abstract:

How to determine if an object has a particular property

Answer:

The first hasprop will return True if a property of name prop exists, eg. hasprop(MyLabel,'Caption') will return true while hasprop(MyEdit,'Caption') will return false. The second one will set property prop to string value s if it exists and is a string type property.

function hasprop(comp: TComponent; const prop: string): Boolean;
var
  proplist: PPropList;
  numprops, i: Integer;
begin
  result := false;
  getmem(proplist, getTypeData(comp.classinfo)^.propcount * Sizeof(Pointer));
  try
    NumProps := getproplist(comp.classInfo, tkProperties, proplist);
    for i := 0 to pred(NumProps) do
    begin
      if comparetext(proplist[i]^.Name, prop) = 0 then
      begin
        result := true;
        break;
      end;
    end;
  finally
    freemem(proplist, getTypeData(comp.classinfo)^.propcount * Sizeof(Pointer));
  end;
end;

procedure setcomppropstring(comp: TComponent; const prop, s: string);
var
  proplist: PPropList;
  numprops, i: Integer;
begin
  getmem(proplist, getTypeData(comp.classinfo)^.propcount * Sizeof(Pointer));
  try
    NumProps := getproplist(comp.classInfo, tkProperties, proplist);
    for i := 0 to pred(NumProps) do
    begin
      if (comparetext(proplist[i]^.Name, prop) = 0) and
        (comparetext(proplist[i]^.proptype^.name, 'string') = 0 then
        begin
          setStrProp(comp, proplist[i], s);
          break;
        end;
    end;
  finally
    freemem(proplist, getTypeData(comp.classinfo)^.propcount * Sizeof(Pointer));
  end;
end;

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