how to add objects to virtualtreeview

问题

In short, I'm trying to add Object into VirtualTreeView but am always getting error EAccessViolation at CellText I'm wondering about the reason for the error i tried to do my best but without result...

this is my attempt:

 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;

回答1:

It looks like the OnGetText event is being fired before the TPerson object has been created. Try checking that the object isn't nil first:

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;

回答2:

I would change this:

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;

and this:

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;

来源：https://stackoverflow.com/questions/14136951/how-to-add-objects-to-virtualtreeview

标签

Delphi

virtualtreeview