Delphi：重写方法没有调用使用RTTI实例化的对象

您没有将Clone变量初始化为nil.我的机器上的哪个导致上层CloneInstance方法中的访问冲突,因为没有创建克隆,因为传入的值是非零的.

您没有将DestinationInstance参数声明为var.这意味着上层CloneInstance方法中的实例化不会返回给调用者.将var添加到参数可以解决问题.你需要在程序的main方法中调用CloneInstance时使用TObject(Clone),否则Delphi会抱怨“没有可以使用这些参数调用的重载方法”.这是因为var参数需要将它们的确切声明类型传递给它们.

我将您的代码更改为：

uses
  SysUtils,rtti;

type
  TPerson = class(TObject)
  public
    Name: string;
    constructor Create;
    destructor Destroy(); Override;
  end;

constructor TPerson.Create;
begin
  WriteLn('A TPerson was created');
end;

destructor TPerson.Destroy;
begin
  WriteLn('A TPerson was freed.');
  inherited;
end;

procedure CloneInstance(SourceInstance: TObject; var DestinationInstance: TObject; Context: TRttiContext); Overload;
var
  rSourceType:      TRttiType;
  rDestinationType: TRttiType;
  rField:           TRttiField;
  rSourceValue:     TValue;
  Destination:      TObject;
  rMethod:          TRttiMethod;
begin
  rSourceType := Context.GetType(SourceInstance.ClassInfo);
  if (DestinationInstance = nil) then begin
    rMethod := rSourceType.GetMethod('Create');
    DestinationInstance := rMethod.Invoke(rSourceType.AsInstance.MetaclassType,rField.GetValue(SourceInstance));
    end;
  end;
end;

procedure CloneInstance(SourceInstance: TObject; var DestinationInstance: TObject); Overload;
var
  rContext:       TRttiContext;
begin
  rContext := TRttiContext.Create();
  CloneInstance(SourceInstance,rContext);
  rContext.Free();
end;

var
  Original:     TPerson;
  Clone:        TPerson;
begin
  Clone := nil;
  ReportMemoryLeaksOnShutdown := true;
  Original := TPerson.Create();
  Original.Name := 'Marjan';

  CloneInstance(Original,TObject(Clone));
  Original.Name := 'Original';
  WriteLn('Original name: ',Original.Name);
  WriteLn('Clone name: ',Clone.Name);

  Clone.Free();
  Original.Free();
  ReadLn;
end.

我添加了一个构造函数来查看正在创建的两个实例以及在克隆之后检查名称的几行.输出如下：

A TPerson was created
A TPerson was created
Original name: Original
Clone name: Marjan
A TPerson was freed.
A TPerson was freed.