Why does Memo.Lines
use the abstract class TStrings
? Why doesn't it use TStringList
instead?
And should I convert it to TStringList
before working with it?
TMemo.Lines
, TListBox.Items
, TComboBox.Items
, etc. ; all are declared as TStrings
. Beware, talking about the property that is! The internal created types are TMemoStrings
, TListBoxStrings
and TComboBoxStrings
respectively, which are all descendants of TStrings
and differ all in way of storage.
And why? For interchangeability and interoperability. So every TStrings
-descendant has the same properties, and so you can do:
Memo1.Lines := ListBox1.Items;
How to use? Well, a TStrings
property like TMemo.Lines
works just fine. You can add, delete, change, renew and clear the strings (and objects) on the property, because internally it is a TMemoStrings
which implements all this interaction. Declaration <> implementation.
But when you want any special handling, e.g. like sorting which TStringList
provides, then you need help. You cannot typecast nor convert a TMemo.Lines
to a TStringList
, because it isn't one, but instead you need to create an intermediate object for this special processing:
var
Temp: TStringList;
begin
Temp := TStringList.Create;
try
Temp.Assign(Memo1.Lines);
Temp.Sort;
Memo1.Lines.Assign(Temp);
finally
Temp.Free;
end;
end;