Delphi 2010中的rtti数据操作和一致性 [英] Rtti data manipulation and consistency in Delphi 2010

问题描述

有人知道吗，如何使用对原始数据的引用来创建TValue?在我的序列化项目中，我使用(如 XML-Serialization中所建议)是一种通用序列化程序，它将TValues存储在内部树结构中(类似于示例中的MemberMap).

Has anyone an idea, how I can make TValue using a reference to the original data? In my serialization project, I use (as suggested in XML-Serialization) a generic serializer which stores TValues in an internal tree-structure (similar to the MemberMap in the example).

此成员树还应用于创建动态设置表单并处理数据. 我的想法是为数据定义一个属性:

This member-tree should also be used to create a dynamic setup form and manipulate the data. My idea was to define a property for the Data:

TDataModel <T> = class
  {...}
  private
    FData : TValue;
    function GetData : T;
    procedure SetData (Value : T);
  public
    property Data : T read GetData write SetData;
end;

GetData，SetData方法的实现:

The implementation of the GetData, SetData Methods:

procedure TDataModel <T>.SetData (Value : T);

begin
FData := TValue.From <T> (Value);
end;

procedure TDataModel <T>.GetData : T;

begin
Result := FData.AsType <T>;
end;

不幸的是，TValue.From方法始终会复制原始数据.因此，每当应用程序对数据进行更改时，DataModel都不会更新，反之亦然，如果我以动态形式更改DataModel，原始数据也不会受到影响. 当然，在更改任何东西之前和之后，我总是可以使用Data属性，但是由于我在DataModel中使用了很多Rtti，所以我真的不想在任何时候这样做.

Unfortunately, the TValue.From method always makes a copy of the original data. So whenever the application makes changes to the data, the DataModel is not updated and vice versa if I change my DataModel in a dynamic form, the original data is not affected. Sure I could always use the Data property before and after changing anything, but as I use lot of Rtti inside my DataModel, I do not realy want to do this anytime.

也许有人有更好的建议?

Perhaps someone has a better suggestion?

推荐答案

TValue旨在以非常紧凑的形式保存任何类型的数据，而并非旨在模拟指针".看一下RTTI.pas单元:TValue是一个RECORD，只有一个TValueData类型的数据成员. TValueData本身本身就是一个变体记录.

A TValue is designed to hold any kind of data in a very compact form, it's not designed to emulate an "pointer". Take a look in the RTTI.pas unit: TValue is a RECORD that only has one data member of the type TValueData. TValueData itself is itself a variant record.

查看TValueData，您将看到它除了最小的数据量外什么都不保存:没有办法知道TValue的来源.

Looking at TValueData you will see how it does NOT hold anything but the minimum amount of data: There's no way to know where that TValue came from.

解决方案:不要在您的结构中持有TValue，而是将其替换为一对TRttiField +一个TObject.当您需要TValue时，请使用TRttiField.GetValue(Instance)，当您要设置值时，请使用TRttiField.SetValue(Instance，AValue:TValue).

The solution: Don't hold a TValue in your structures, replace it with a pair of TRttiField + an TObject. When you need the TValue use TRttiField.GetValue(Instance), when you want to set a value use TRttiField.SetValue(Instance, AValue:TValue).

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