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    copied!<p>In addition to the answer to this question, I've posted a workaround to your previous question here: <a href="https://stackoverflow.com/questions/7528829/generics-and-marshal-unmarshal-what-am-i-missing-here/7810038#7810038">Generics and Marshal / UnMarshal. What am I missing here?</a></p> <p>For some reason, using the non-default constructor of the TJsonobject causes the issue in XE2 - using the default constructor "fixed" the problem.</p> <p>First, you need to move your TTestobject to its own unit - otherwise, RTTI won't be able to find/create your object when trying to unmarshal.</p> <pre><code> 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. </code></pre> <p>Also note that the constructor has been overloaded - this allows you to see that the code is functional without pre-pouplating the data in the object during creation.</p> <p>Here is the implementation for the generic class list object</p> <pre><code> unit uTestObjectList; interface uses SysUtils, Classes, Contnrs, Generics.Defaults, Generics.Collections, DbxJson, DbxJsonReflect, uTestObject; type {$RTTI EXPLICIT METHODS([]) PROPERTIES([]) FIELDS([])} TTestObjectList&lt;T:TTestObject,constructor&gt; = class(TObjectList&lt;T&gt;) public function Marshal: TJSonObject; constructor Create; class function Unmarshal(value: TJSONObject): TTestObjectList&lt;T&gt;; 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&lt;TTestObject&gt;; implementation { TTestObjectList&lt;T&gt; } constructor TTestObjectList&lt;T&gt;.Create; begin inherited Create; //removed the add for test data - it corrupts unmarshaling because the data is already present at creation end; function TTestObjectList&lt;T&gt;.Marshal: TJSonObject; var Marshal: TJsonMarshal; begin Marshal := TJSONMarshal.Create; try Marshal.RegisterConverter(TTestObjectList&lt;T&gt;, function(Data: TObject): TListOfObjects var I: integer; begin SetLength(Result,TTestObjectlist&lt;T&gt;(Data).Count); for I:=0 to TTestObjectlist&lt;T&gt;(Data).Count-1 do Result[I]:=TTestObjectlist&lt;T&gt;(Data)[I]; end ); Result := Marshal.Marshal(Self) as TJSONObject; finally Marshal.Free; end; end; class function TTestObjectList&lt;T&gt;.Unmarshal(value: TJSONObject): TTestObjectList&lt;T&gt;; var Mar: TJSONUnMarshal; L: TStringList; begin Mar := TJSONUnMarshal.Create(); try Mar.RegisterReverter(TTestObjectList&lt;T&gt;, function(Data: TListOfObjects): TObject var I, Count: Integer; begin Count := Length(Data); Result:=TTestObjectList&lt;T&gt;.Create; for I := 0 to Count - 1 do TTestObjectList&lt;T&gt;(Result).Unmarshal(TJSONObject(Data[I])); end ); //UnMarshal will attempt to create a TTestObjectList&lt;TTestObject&gt; 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&lt;T&gt;; finally Mar.Free; end; end; initialization //force delphi RTTI into maintaining the Generic class information in memory x:=TTestObjectList&lt;TTestObject&gt;.Create; finalization X.Free; end. </code></pre> <p>There are several things that are important to note: If a generic class is created at runtime, RTTI information is NOT kept unless there is a globally accessible object reference to that class in memory. See here: <a href="https://stackoverflow.com/questions/2559049/delphi-rtti-and-tobjectlisttobject">Delphi: RTTI and TObjectList&lt;TObject&gt;</a></p> <p>So, the above unit creates such a variable and leaves it instantiated as discussed in the linked article.</p> <p>The main procedure has been updated that shows both marshaling and unmarshaling the data for both objects:</p> <pre><code> procedure Main; var aTestobj, bTestObj, cTestObj : TTestObject; aList, bList : TTestObjectList&lt;TTestObject&gt;; 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&lt;TTestObject&gt;.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&lt;TTestObject&gt;.Unmarshal(cJSonObject) as TTestObjectList&lt;TTestObject&gt;; for cTestObj in bList do begin writeln(cTestObj.List.Text); end; writeln('TTestObjectList&lt;TTestObject&gt; marshaling complete.'); Readln; end; </code></pre>
 

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