RegisterType

Register new object for streaming.

Declaration

Source position: objects.pp line 667

Description

RegisterType registers a new type for streaming. An object cannot be streamed unless it has been registered first. The stream record S needs to have the following fields set:

ObjType: Sw_Word

This should be a unique identifier. Each possible type should have it's own identifier.

VmtLink: pointer

This should contain a pointer to the VMT (Virtual Method Table) of the object you try to register.

Load : Pointer

is a pointer to a method that initializes an instance of that object, and reads the initial values from a stream. This method should accept as it's sole argument a PStream type variable.

Store: Pointer

is a pointer to a method that stores an instance of the object to a stream. This method should accept as it's sole argument a PStream type variable.

The VMT of the object can be retrieved with the following expression:

VmtLink: Ofs(TypeOf(MyType)^);

Errors

In case of error (if a object with the same ObjType) is already registered), run-time error 212 occurs.

Example

Unit MyObject;


Interface

Uses Objects;

Type
     PMyObject = ^TMyObject;
     TMyObject = Object(TObject)
       Field : Longint;
       Constructor Init;
       Constructor Load (Var Stream : TStream);
       Destructor Done;
       Procedure Store (Var Stream : TStream);
       Function  GetField : Longint;
       Procedure SetField (Value : Longint);
       end;

Implementation

Constructor TMyobject.Init;

begin
  Inherited Init;
  Field:=-1;
end;

Constructor TMyobject.Load (Var Stream : TStream);

begin
  Stream.Read(Field,Sizeof(Field));
end;

Destructor TMyObject.Done;

begin
end;

Function TMyObject.GetField : Longint;

begin
  GetField:=Field;
end;

Procedure TMyObject.SetField (Value : Longint);

begin
  Field:=Value;
end;

Procedure TMyObject.Store (Var Stream : TStream);

begin
  Stream.Write(Field,SizeOf(Field));
end;

Const MyObjectRec : TStreamRec = (
        Objtype : 666;
        vmtlink : Ofs(TypeOf(TMyObject)^);
        Load : @TMyObject.Load;
        Store : @TMyObject.Store;
        );

begin
  RegisterObjects;
  RegisterType (MyObjectRec);
end.