Ensure that every node in a TTreeView is unique

Problem/Question/Abstract:

I want to make sure that every node in my TreeView is unique - like making a new folder in Windows Explorer.

Answer:

It is a timing issue, it looks like you cannot set the node back to edit mode in the onEdited event. So post a user message to the form and set the node to edit mode in the handler for this message:

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls, ComCtrls;

const
  UM_EDITNODE = WM_USER;
type
  TUmEditNode = record
    msg: Cardinal;
    node: TTreenode;
    unused: Longint;
    result: Longint;
  end;

  TForm1 = class(TForm)
    Edit1: TEdit;
    Edit2: TEdit;
    TreeView1: TTreeView;
    procedure TreeView1Edited(Sender: TObject; Node: TTreeNode; var S: string);
  private
    { Private declarations }
    procedure UMEditNode(var msg: TUMeditNode); message UM_EDITNODE;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.TreeView1Edited(Sender: TObject; Node: TTreeNode; var S: string);
var
  n: TTreenode;
begin
  n := (Sender as TTreeview).Items[0];
  while n <> nil do
  begin
    if n <> Node then
    begin
      if AnsiCompareText(n.Text, S) = 0 then
      begin
        ShowMessage('Item already exists, use different text');
        S := node.text;
        PostMessage(handle, UM_EDITNODE, integer(node), 0);
        break;
      end;
    end;
    n := n.GetNext;
  end;
end;

procedure TForm1.UMEditNode(var msg: TUMeditNode);
begin
  if assigned(msg.node) then
    msg.node.edittext;
end;

end.