The following code defines a component class (TStreamable class) and a persistent class (TContainedClass) that is the type of a property on the component class. When a button is clicked, an instance of the component class is created, saved to a file, deleted, and then loaded from the file. By setting a breakpoint on the property setter of the TContainedClass SomeData property, you can watch how the streaming system sets property values when it reads them from a file.
The following unit defines the classes to stream:
unit StrmExmpl;
{$R-,T-,H+,X+}
interface
uses Classes
type
TContainedClass = class(TPersistent)
private:
FSomeData: Integer;
procedure SetSomeData(Value: Integer);
public:
constructor Create; override;
// Only published properties
// are automatically streamed.
published:
property SomeData: Integer read FSomeData write SetSomeData;
end;
TStreamableClass = class(TComponent)
private:
FContainedClass: TContainedClass;
public:
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
// Only published properties
// are automatically streamed.
published:
property ContainedClass: TContainedClass read FContainedClass write FContainedClass;
end;
implementation
procedure TContainedClass.SetSomeData(Value: Integer);
begin
{ Place a breakpoint here and notice how the data is streamed back. }
FSomeData := Value;
end;
constructor TContainedClass.Create;
begin
FSomeData := 42;
end;
constructor TStreamableClass.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
FContainedClass = TContainedClass.Create;
end;
destructor TStreamableClass.Destroy;
begin
FContainedClass.Free;
end;
initialization
RegisterClasses([TContainedClass, TStreamableClass]);
finalization
end.
The following OnClick event handler should be added to a button on the application抯 main form. It causes the above classes to be streamed out and in. Note that you must add StrmExmpl to the uses clause of unit1.
procedure TForm1.Button1Click(Sender: TObject);
var
AClassInstance: TStreamableClass;
begin
AClassInstance := TStreamableClass.Create(nil);
WriteComponentResFile('C:/Test', AClassInstance);
FreeAndNil(AClassInstance);
AClassInstance := ReadComponentResFile('C:/Test', nil) as TStreamableClass;
FreeAndNil(AClassInstance);
end;
