delphi – 当我重新排列TObjectList时,为什么会出现“无效指针操

type 
  TCustomList = class(TObjectList)
  private
    function GetItem(AIndex: Integer): TMyObject; // virtual;
    procedure SetItem(Index: Integer; AObject: TMyObject);
...
  public
    property Items[Index: Integer]: TMyObject read GetItem write SetItem;
    procedure InsertSort();
  end;

通过以下实现：

implementation

function TCustomList.GetItem(AIndex: Integer): TMyObject;
begin
  Result := TMyObject(inherited Items[AIndex]);
end;

procedure TCustomList.SetItem(Index: Integer; AObject: TMyObject);
begin
    inherited Items[Index]:= AObject;
end;

procedure TCustomList.InsertSort;
var
  i,j: integer;
  key: TMyObject;
begin
  for j := 1 to self.Count - 1 do
  begin
    key:= self.Items[j];
    i := j - 1;
    while ((i >= 0) AND (self.Items[i].Compare(key)>0)) do
    begin
        self.Items[i+1]:= self.Items[i]; // does not WORK!!! properly.. System.Contnrs problem ?? 
        i := i-1;
    end; // while
    self.Items[i+1]:= key;
  end; // for
end; // procedure InsertSort

当我在TMyObject的一组实例上运行代码时,我得到一个无效的指针操作异常.我认为,这是由于通过Items属性读取和写入TCustomList的元素造成的.

为什么会出现这个无效指针操作异常？