当文本有三行或更多行时，我如何知道是否在TRichEdit中选择了所有文本？

function IsAllTextSelected(richEdit: TRichEdit): Boolean;
var
  startLine, endLine, selectedLines: Integer;
begin
  // 获取选择的起始行号
  startLine := richEdit.Perform(EM_LINEFROMCHAR, richEdit.SelStart, 0);
  // 获取选择的结束行号
  endLine := richEdit.Perform(EM_LINEFROMCHAR, richEdit.SelStart + richEdit.SelLength, 0);
  // 计算选择的行数
  selectedLines := endLine - startLine + 1;
  // 判断是否选择了所有文本
  Result := (startLine + selectedLines) = richEdit.Lines.Count;
end;

if IsAllTextSelected(RichEdit1) then
  ShowMessage('已选择所有文本')
else
  ShowMessage('未选择所有文本');