德尔福 – 泛型和元帅/ UnMarshal.我在这里错过了什么？第2部分 ：-)

跟进我之前的问题：
   Generics and Marshal / UnMarshal. What am I missing here?

在“第1部分”(上面的链接)中,TOndrej提供了一个很好的解决方案 – 在XE2上失败了.
在这里,我提供纠正的来源来纠正这一点

而且我认为有必要进一步扩展这个问题.
所以我想听听大家如何做到这一点：

首先 – 要在XE2和XE2更新1上运行源,请进行以下更改：

Marshal.RegisterConverter(TTestObject,
  function (Data: TObject): String // <-- String here
  begin
    Result := T(Data).Marshal.ToString; // <-- ToString here
  end
  );

为什么？
我能看到的唯一原因必须与XE2有关,因为它有更多可用的RTTI信息.因此它将尝试并封送返回的TObject.
我在这里走在正确的轨道上吗？请随意发表评论.

更重要的是 – 该示例未实现UnMarshal方法.
如果有人可以制作一个并在此发布我会喜欢它:-)

我希望你仍然对这个问题感兴趣.

亲切的问候
比亚

除了这个问题的答案之外,我在这里发布了一个解决方法： Generics and Marshal / UnMarshal. What am I missing here?

出于某种原因,使用TJsonobject的非默认构造函数导致XE2中的问题 – 使用默认构造函数“修复”问题.

首先,您需要将TTestobject移动到自己的单元 – 否则,在尝试解组时,RTTI将无法找到/创建您的对象.

unit uTestObject;

    interface

    uses
      SysUtils, Classes, Contnrs, Generics.Defaults, Generics.Collections, DbxJson, DbxJsonReflect;

    type
      {$RTTI EXPLICIT METHODS([]) PROPERTIES([vcPublished]) FIELDS([vcPrivate])}
      TTestObject=class(TObject)
      private
        aList:TStringList;
      public
        constructor Create; overload;
        constructor Create(list: array of string); overload;
        constructor Create(list:TStringList); overload;
        destructor Destroy; override;
        function Marshal:TJSonObject;
        class function Unmarshal(value: TJSONObject): TTestObject;
      published
        property List: TStringList read aList write aList;
      end;

    implementation

    { TTestObject }

    constructor TTestObject.Create;

    begin
      inherited Create;
      aList:=TStringList.Create;
    end;

    constructor TTestObject.Create(list: array of string);

    var
      I:Integer;

    begin
      Create;
      for I:=low(list) to high(list) do
        begin
          aList.Add(list[I]);
        end;
    end;

    constructor TTestObject.Create(list:TStringList);

    begin
      Create;
      aList.Assign(list);
    end;

    destructor TTestObject.Destroy;

    begin
      aList.Free;
      inherited;
    end;

    function TTestObject.Marshal:TJSonObject;

    var
      Mar:TJSONMarshal;

    begin
      Mar:=TJSONMarshal.Create();
      try
        Mar.RegisterConverter(TStringList,
          function(Data:TObject):TListOfStrings

          var
            I, Count:Integer;
          begin
            Count:=TStringList(Data).Count;
            SetLength(Result, Count);
            for I:=0 to Count-1 do
              Result[I]:=TStringList(Data)[I];
          end);
        Result:=Mar.Marshal(Self) as TJSonObject;
      finally
        Mar.Free;
      end;
    end;

    class function TTestObject.Unmarshal(value: TJSONObject): TTestObject;

    var
      Mar: TJSONUnMarshal;
      L: TStringList;

    begin
      Mar := TJSONUnMarshal.Create();
      try
        Mar.RegisterReverter(TStringList,
          function(Data: TListOfStrings): TObject

          var
            I, Count: Integer;
          begin
            Count := Length(Data);
            Result:=TStringList.Create;
            for I := 0 to Count - 1 do
              TStringList(Result).Add(string(Data[I]));
          end
        );
        //UnMarshal will attempt to create a TTestObject from the TJSONObject data
        //using RTTI lookup - for that to function, the type MUST be defined in a unit
        Result:=Mar.UnMarshal(Value) as TTestObject;
      finally
        Mar.Free;
      end;
    end;

    end.

另请注意,构造函数已经过载 – 这使您可以在创建过程中看到代码是有用的,而无需预先设置对象中的数据.

这是泛型类列表对象的实现

unit uTestObjectList;

    interface

    uses
      SysUtils, Classes, Contnrs, Generics.Defaults, Generics.Collections,
      DbxJson, DbxJsonReflect, uTestObject;

    type
      {$RTTI EXPLICIT METHODS([]) PROPERTIES([]) FIELDS([])}
      TTestObjectList<T:TTestObject,constructor> = class(TObjectList<T>)
      public
        function Marshal: TJSonObject;
        constructor Create;
        class function Unmarshal(value: TJSONObject): TTestObjectList<T>; static;
      end;

    //Note: this MUST be present and initialized/finalized so that
    //delphi will keep the RTTI information for the generic class available
    //also, it MUST be "project global" - not "module global"
    var
      X:TTestObjectList<TTestObject>;

    implementation

    { TTestObjectList<T> }
    constructor TTestObjectList<T>.Create;
    begin
      inherited Create;
      //removed the add for test data - it corrupts unmarshaling because the data is already present at creation
    end;

    function TTestObjectList<T>.Marshal: TJSonObject;
    var
      Marshal: TJsonMarshal;
    begin
      Marshal := TJSONMarshal.Create;
      try
        Marshal.RegisterConverter(TTestObjectList<T>,
          function(Data: TObject): TListOfObjects
          var
            I: integer;

          begin
            SetLength(Result,TTestObjectlist<T>(Data).Count);
            for I:=0 to TTestObjectlist<T>(Data).Count-1 do
              Result[I]:=TTestObjectlist<T>(Data)[I];
          end
        );
        Result := Marshal.Marshal(Self) as TJSONObject;
      finally
        Marshal.Free;
      end;
    end;

    class function TTestObjectList<T>.Unmarshal(value: TJSONObject): TTestObjectList<T>;

    var
      Mar: TJSONUnMarshal;
      L: TStringList;

    begin
      Mar := TJSONUnMarshal.Create();
      try
        Mar.RegisterReverter(TTestObjectList<T>,
          function(Data: TListOfObjects): TObject
          var
            I, Count: Integer;
          begin
            Count := Length(Data);
            Result:=TTestObjectList<T>.Create;
            for I := 0 to Count - 1 do
              TTestObjectList<T>(Result).Unmarshal(TJSONObject(Data[I]));
          end
        );
        //UnMarshal will attempt to create a TTestObjectList<TTestObject> from the TJSONObject data
        //using RTTI lookup - for that to function, the type MUST be defined in a unit,
        //and, because it is generic, there must be a GLOBAL VARIABLE instantiated
        //so that Delphi keeps the RTTI information avaialble
        Result:=Mar.UnMarshal(Value) as TTestObjectList<T>;
      finally
        Mar.Free;
      end;
    end;


    initialization
      //force delphi RTTI into maintaining the Generic class information in memory
      x:=TTestObjectList<TTestObject>.Create;

    finalization
      X.Free;

    end.

有几件事需要注意：
如果在运行时创建泛型类,则不保留RTTI信息,除非在内存中存在对该类的全局可访问对象引用.见：Delphi: RTTI and TObjectList<TObject>

因此,上面的单元创建了这样一个变量,并将其实例化,如链接文章中所讨论的那样.

主要过程已更新,显示两个对象的数据编组和解组：

procedure Main;
    var
      aTestobj,
      bTestObj,
      cTestObj : TTestObject;
      aList,
      bList : TTestObjectList<TTestObject>;
      aJsonObject,
      bJsonObject,
      cJsonObject : TJsonObject;

      s: string;

    begin
      aTestObj := TTestObject.Create(['one','two','three','four']);
      aJsonObject := aTestObj.Marshal;
      s:=aJsonObject.ToString;
      Writeln(s);

      bJsonObject:=TJsonObject.Create;
      bJsonObject.Parse(BytesOf(s),0,length(s));

      bTestObj:=TTestObject.Unmarshal(bJsonObject) as TTestObject;
      writeln(bTestObj.List.Text);

      writeln('TTestObject marshaling complete.');
      readln;

      aList := TTestObjectList<TTestObject>.Create;
      aList.Add(TTestObject.Create(['one','two']));
      aList.Add(TTestObject.Create(['three']));
      aJsonObject := aList.Marshal;
      s:=aJsonObject.ToString;
      Writeln(s);

      cJSonObject:=TJsonObject.Create;
      cJSonObject.Parse(BytesOf(s),0,length(s));
      bList:=TTestObjectList<TTestObject>.Unmarshal(cJSonObject) as TTestObjectList<TTestObject>;
      for cTestObj in bList do
        begin
          writeln(cTestObj.List.Text);
        end;

      writeln('TTestObjectList<TTestObject> marshaling complete.');
      Readln;
    end;