how to add objects to virtualtreeview

Question

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;

I'm not familiar with TVirtualStringtree, but I'd expect here: PersonRec := VirtualStringTree1.GetNodeData(VirtualStringTree1.AddChild(VirtualStringTree1.RootNode)); >> pointing PersonRec to NIL. Same here in your code: PersonRec := VirtualStringTree1.GetNodeData(VirtualStringTree1.AddChild(nil)); — bummi, Jan 03 '13 at 11:07

score 2 · Accepted Answer · answered Jan 03 '13 at 12:22

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;

score 0 · Answer 2 · answered Jan 03 '13 at 10:52

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;

It works for me on windows 7 Delphi 2010. You have to add at least one column on VirtualStringTree1. Go to Object Inspector->Header->Columns. Otherwise you get Access Violation. Or add if Assigned(PersonRec.PersonObj) then CellText := PersonRec.PersonObj.Name; — AvgustinTomsic, Jan 03 '13 at 11:18

how to add objects to virtualtreeview

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