彩票走势图

VirtualDAC组件由TDataSet发展而来，它是没有链接数据文件的内存数据存储库。使用AddField方法向虚拟表添加字段。创建虚拟表后，它将立即为空。然后，用户就可以定义新字段或加载现有表文件，以便虚拟表对象初始化并准备打开。关闭虚拟表时，它将丢弃其记录集。为了保留用户在设计时输入的数据供以后使用，用户可能希望在Options属性中包含voStored选项。在运行时，用户需要显式调用SaveToFile方法以存储对文件的修改，以后可以通过调用LoadFromFile方法将其检索回虚拟表。

TVirtualTable component is TDataSet descendant. It represents an in-memory data storage that does not have linked data files. To add fields to virtual table call AddField method. Immediately after creating virtual table it will be empty. You then define new fields or load existing table files so that virtual table object becomes initialized and ready to be opened. When you close virtual table it will discard its record set. To keep data you entered at design-time for later use you may wish to include voStored option in Options property. At run-time you need to call SaveToFile method explicitly to store modifications to the file that later may be retrieved back into the virtual table by calling LoadFromFile method.