Am I correct that TFPObjectlist is kind of like Tstringlist, except instead of creating and array of strings, it creates an array of objects?

I'm wanting to do something like that but I don't know how to define the object.. I'm guessing it would be something like a record

I'm wanting to end up with a list of records like:
Type
   test = record
      Port             :String;
      Size             :Byte;
      Status           :Word;
   End;

Does anyone have an example of how to use TFPObjectlist?

James

On Sep 7, 2020, at 6:07 AM, James Richters via fpc-pascal wrote: Does anyone have an example of how to use TFPObjectlist?

It just frees objects that are removed from the list (or when the list is freed).

list:= TFPObjectlist.Create;
list.Add(TObject.Create);
list.Free;

in that example the object added to the list won't leak memory but it will be freed when the list itself is freed.

or

list:= TFPObjectlist.Create;
list.Add(TObject.Create);
list.Delete(0);

will also not leak memory.

Regards,
Ryan Joseph

Hi,
 
I used TFPObjectList only once, for visual component TECAccordion (https://wiki.lazarus.freepascal.org/Eye-Candy_Controls#TECAccordion). Each item of list is derived from TWinControl so it is possible to use it even for visual components (like TCollection).  
However, in your case (records) I would rather use TFPGList from FGL unit:  
1) add {$modeswitch ADVANCEDRECORDS}
2) add FGL to uses3) define class operator =test = record    Port :String;    Size :Byte;    Status :Word;    class operator = (A,B: test): Boolean;  End; 4) implement itclass operator test.=(A, B: test): Boolean;begin  Result:=(A.Port=B.Port) and (A.Size=B.Size);  // and ...end;   5) define specialized list:   TMyL = specialize TFPGList<test>;
6) create it
  MyList: TMyL;
  ...
  MyList:=TMyL.Create;
 
Now you can work with it comfortably
MyList[1].Port:='abc';
 
V.
______________________________________________________________

James

Hi,
 
some crippled formatting, so again:
 
However, in your case (records) I would rather use TFPGList from FGL unit:  
1) add {$modeswitch ADVANCEDRECORDS}
 
2) add FGL to uses
3) define class operator =
test = record    Port :String;    Size :Byte;    Status :Word;    class operator = (A,B: test): Boolean;  End; 4) implement itclass operator test.=(A, B: test): Boolean;begin  Result:=(A.Port=B.Port) and (A.Size=B.Size);  // and ...end;   5) define specialized list:  
  TMyL = specialize TFPGList<test>;
 
6) create it
 
  MyList: TMyL;
 
  ...
 
  MyList:=TMyL.Create;
 
Now you can work with it comfortably
 
MyList[1].Port:='abc';
 
V.
______________________________________________________________

______________________________________________________________

James

What’s the difference between TList and TFPGList? Which one is better for this example?

James

James Richters via fpc-pascal schrieb am
Di., 8. Sep. 2020, 20:07:

What’s the difference between TList and TFPGList? Which one is better for this example?

The main difference is that TFPGList ist a generic, thus when you specialize it with your record you'll have a typesafe object where you don't need to manually work with pointers while for TList you either need to work with pointers or declare a descendant with typesafe setters/getters like you had done in the other mail.
You could also take a look at the generic TList in Generics.Collections which does not require an = operator like TFPGList does.

Please note that if you work with TFPGList or the Generics.Collection.TList then you need to modify an entry using a local variable if your entries are records:

entry := mylist[i];
entry.field := entry.field * 2;
mylist[i] := entry;

This is because the getter for the Items property will provide a /copy/ of the entry.

With Classes.TList you'd use a pointer however and thus you can modify it in place.

Regards,
Sven