Delphi - Must I free all elements inside TObject before release itself? - list

Question

Please, about this code:
type
TClient = class(TObject)
public
Host: String;
Queue: TIdThreadSafeStringList;
end;
var
Clients: TThreadList;
procedure TMain.FormCreate(Sender: TObject);
const
Hosts: Array[0..4] of String = (
'HOST1', 'HOST2', 'HOST3', 'HOST4, 'HOST5'
);
var
I: Integer;
List: TList;
Client: TClient;
begin
Clients := TThreadList.Create;
Clients.Duplicates := dupAccept;
for I := Low(Hosts) to High(Hosts) do
begin
Client := TClient.Create;
Client.Host := Hosts[I];
Client.Queue := TIdThreadSafeStringList.Create;
Clients.Add(Client);
Client := nil;
end;
end;
I would like to know if the correct way of releasing it memory is:
procedure TMain.FormDestroy(Sender: TObject);
var
I: Integer;
List: TList;
begin
List := Clients.LockList;
try
for I := 0 to List.Count - 1 do
TClient(List[I]).Free;
finally
Clients.UnlockList;
Clients.Free;
end;
end;
Or maybe like this:
procedure TMain.FormDestroy(Sender: TObject);
var
I: Integer;
List: TList;
begin
List := Clients.LockList;
try
for I := 0 to List.Count - 1 do
begin
TClient(List[I]).Queue.Free;
TClient(List[I]).Free;
end;
finally
Clients.UnlockList;
Clients.Free;
end;
end;
In other words, I would like to know if when I release an object (TClient) all elements (Queue) are released automatically, or must I do it manually.
Thanks!

Answer 1

The queue object needs to be destroyed when the client object is destroyed. However, the correct way to do this is to make the client class take charge of its members.
type
TClient = class
private
FHost: String;
FQueue: TIdThreadSafeStringList;
public
constructor Create(const Host: string);
destructor Destroy; override;
end;
....
constructor TClient.Create(const Host: string);
begin
inherited Create;
FQueue := TIdThreadSafeStringList.Create;
FHost := Host;
end;
destructor TClient.Destroy;
begin
FQueue.Free;
inherited;
end;
If you do it this way then it's not possible to instantiate the class and fail to instantiate its members. Do it your way, and every time you need to instantiate the class then you have to repeat the code to instantiate the members. It's just all too easy to make a mistake that way. What's more it makes the code harder to read and maintain.