将 nil 赋给 TImage.Picture.Graphic 来清除图片后，如何再次使用它？

Question

在下面的代码中，我清除了btnSaveClick中的图片，稍后在btnLoadClick中我想将图片分配给图像，但它给出了AV，因为Graphic对象不存在。

我怎样才能完成任务？

procedure TForm1.btnSaveClick(Sender: TObject);
var
  fs: TFileStream;
  s:  TMemoryStream;
  buf: TBytes;
  z:  integer;
begin
  fs := TFileStream.Create('c:\temp\a.my', fmCreate);
  s  := TMemoryStream.Create;
  try
    Image1.Picture.Graphic.SaveToStream(s);
    z := s.Size;
    SetLength(buf, z);
    s.Position := 0;
    s.ReadBuffer(buf[0], z);

    fs.WriteBuffer(z, SizeOf(integer));
    fs.WriteBuffer(buf[0], z);
  finally
    s.Free;
    fs.Free;
  end;

  ShowMessage('ok');

  Image1.Picture.Graphic := nil;
end;

procedure TForm1.btnLoadClick(Sender: TObject);
var
  fs: TFileStream;
  s:  TMemoryStream;
  buf: TBytes;
  z:  integer;
  gc: TGraphicClass;
begin
  fs := TFileStream.Create('c:\temp\a.my', fmOpenRead);
  s  := TMemoryStream.Create;
  try
    fs.ReadBuffer(z, SizeOf(integer));
    SetLength(buf, z);
    fs.ReadBuffer(buf[0], z);
    s.WriteBuffer(buf[0], z);
    s.Position := 0;

    Image1.Picture.RegisterFileFormat('jpg', 'jpeg files', gc);
  //  Image1.Picture.Graphic.LoadFromStream(s);  <-- AV here. Whats the proper way to do it?

  finally
    s.Free;
    fs.Free;
  end;

  ShowMessage('ok');

end;

Answer 1

如果您从扩展名与注册图像类相对应的文件加载，您可以简单地执行以下操作：

Picture.LoadFromFile(FileName);

否则，您可以在代码中创建特定后代的实例TGraphic（取决于您使用的图形类型）并将其分配给Graphic属性，例如对于 JPEG：

var
  Graphic: TJpegImage;
begin
  Graphic := TJpegImage.Create;
  try
    Graphic.LoadFromFile(FileName);
    Picture.Graphic := Graphic;
  finally
    Graphic.Free;
  end;
end;