如何向virtualtreeview添加对象

Question

简而言之，我试图将对象添加到VirtualTreeView中，但在CellText上总是收到错误EAccessViolation。我想知道错误的原因，我试图尽最大努力，但没有结果……

这是我的尝试：

 TForm1 = class(TForm)
 private

 public

 end;

 TPerson = class;

 PPersonNode = ^TPersonNode;
 TPersonNode = record
   PersonObj: TPerson;
 end;

 TPerson = class(TObject)
 private
   FName: string;
 public
   property Name: string read FName write FName;
 end;

 procedure TForm1.Button1Click(Sender: TObject);  
 var
   PersonRec: PPersonNode;
 begin
   PersonRec := VirtualStringTree1.GetNodeData(VirtualStringTree1.AddChild(nil));
   PersonRec.PersonObj := TPerson.Create;
   PersonRec.PersonObj.Name := 'aaa'; 
 end;

 procedure TForm1.VirtualStringTree1GetNodeDataSize(Sender: TBaseVirtualTree;
   var NodeDataSize: Integer);
 begin
   NodeDataSize := SizeOf(TPersonNode);
end;

procedure TForm1.VirtualStringTree1GetText(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex; TextType: TVSTTextType;
var CellText: string);
var
   PersonRec: PPersonNode;
begin
   PersonRec := Sender.GetNodeData(Node);
   CellText := PersonRec.PersonObj.Name;
end;

Answer 1

看起来OnGetText事件是在创建TPerson对象之前触发的。首先尝试检查对象是否为nil：

procedure TForm1.VirtualStringTree1GetText(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex; TextType: TVSTTextType;
var CellText: string);
var
   PersonRec: PPersonNode;
begin
   PersonRec := Sender.GetNodeData(Node);

   if PersonRec <> nil then  // <- check that the object has been created
     CellText := PersonRec.PersonObj.Name;
end;

Answer 2

我会改变这一点：

procedure TForm1.Button1Click(Sender: TObject);  
var
 PersonRec: PPersonNode;
begin
 PersonRec := VirtualStringTree1.GetNodeData(VirtualStringTree1.AddChild(VirtualStringTree1.RootNode));
 PersonRec.PersonObj := TPerson.Create;
 PersonRec.PersonObj.Name := 'aaa'; 
end;

还有这个：

procedure TForm1.VirtualStringTree1GetText(Sender: TBaseVirtualTree;
Node: PVirtualNode; Column: TColumnIndex; TextType: TVSTTextType;
var CellText: string);
var
 PersonRec: PPersonNode;
begin
 if Assigned(Node) then
 begin
  PersonRec := Sender.GetNodeData(Node);
  CellText := PersonRec.PersonObj.Name;
 end;
end;