ReadComponentResFile (Object Pascal)

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Description

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.

Code

{$R-,T-,H+,X+}

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

  TContainedClass = class(TPersistent)
  private
    FSomeData: Integer;
    procedure SetSomeData(Value: Integer);
  public
    constructor Create;
    // 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;

var
  Form1: TForm1;

implementation

{$R *.dfm}

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;

{
The following OnClick event handler should be added to a
button on the applications main form. It causes the above
classes to be streamed out and in.
procedure TForm1.Button1Click(Sender: TObject);
var
  AClassInstance: TStreamableClass;
begin
  AClassInstance := TStreamableClass.Create(nil);
  WriteComponentResFile('Test', AClassInstance);
  FreeAndNil(AClassInstance);

  AClassInstance := Classes.ReadComponentResFile('Test', nil) as TStreamableClass;
  FreeAndNil(AClassInstance);
end;

initialization
  RegisterClasses([TContainedClass, TStreamableClass]);

Uses