[morebeauty]

А где в приведённых кусках кода обращение к TreeView.Selected?
Что такое и где объявлено "frmCat1" и "CatSys"?

Думаю не в этом собака зарыта, но...

В коде фрэйма:

Код:

procedure TfrmCat.btn1Click(Sender: TObject);
var
  SelID:integer;
begin
  //ShowMessage(Self.name + ' ' + IntToStr(CatSys.RootCat) + ' ' + CatSys.TV.Selected.Text);
  if CatSys.TV.Selected<>nil then
  begin
    selid:=Integer(CatSys.TV.Selected.Data);
    CatSys.CreateNewCat('123',SelID);
  end;

end;

procedure TfrmCat.btn4Click(Sender: TObject);
var
  selid:Integer;
begin
  if CatSys.TV.selected<>nil then
  begin
    selid:=Integer(CatSys.TV.Selected.Data);
    CatSys.DeleteCatByID(selid);
  end;
end;

В отдельном юните:

Код:

unit DBCatSystem;

interface

uses
  Variants, Classes, DB, ADODB, ComCtrls, SysUtils, Dialogs;
type
  TCatSystem = class
  private
    FConnection:TADOConnection;
    FCatTableName:string;
    FFieldID:string;
    FFieldCatName:string;
    FFieldCatParent:string;
    FRootCat:Integer;
    FTreeView:TTreeView;
    FShowCatID:Boolean;
    procedure AddTreeNode(Parent:TTreeNode;IDNODE:Integer);
    procedure NotConnected;
  public
    property Connection:TADOConnection read FConnection write FConnection;
    property CatTableName:string read FCatTableName write FCatTableName;
    property ID:string read FFieldID write FFieldID;
    property CatName: string read FFieldCatName write FFieldCatName;
    property CatParent: string read FFieldCatParent write FFieldCatParent;
    property RootCat: Integer read FRootCat write FRootCat;
    property TV:TTreeView read FTreeView write FTreeView;
    property ShowCatID:Boolean read FShowCatID write FShowCatID;
    procedure FeelingTree;
    function GetCatNameByID (CatID:Integer):string;
    procedure RenameCatByID (CatID:Integer;NewName:string);
    procedure DeleteCatByID (CatID:integer);
    function HasChilds (CatID:Integer):Boolean;
    function GetTreeNodeByID(CatID:Integer):TTreeNode;
    procedure CreateNewCat(NewCatName:string;ParentID:Integer);
    function GetChildsIDs(CatID:Integer):TStringList;
  end;
implementation

{ TCatSystem }

procedure TCatSystem.AddTreeNode(Parent: TTreeNode; IDNODE: Integer);
var
  RS:_Recordset;
  SQLStr:string;
  TmpTN:TTreeNode;
  TmpStr:string;
  TmpInt:integer;
  CatIDLabel:string;
begin
  if Connection.Connected=False then
  begin
    NotConnected;
    Exit;
  end;
  SQLStr:='SELECT ' + CatName + ' FROM ' + CatTableName +
  ' WHERE ' + ID + '=' + IntToStr(IDNODE);
  rs:=Connection.Execute(SQLStr);
  if RS.RecordCount=1 then
  begin
    //SetLength(CatIDs,Length(CatIDs)+1);
    //CatIDs[High(catids)]:=ID;
    if ShowCatID then CatIDLabel:=' (' + IntToStr(IDNODE) + ')' else CatIDLabel:='';
    TmpStr:=VarToStr(RS.Fields.Item[CatName].Value) + CatIDLabel;
    tmptn:=TV.Items.AddChildObject(Parent,TmpStr,Pointer(IDNODE));
    TmpTN.SelectedIndex:=1;
    SQLStr:='SELECT ' + ID + ' FROM ' + CatTableName +
    ' WHERE ' + CatParent + '=' + IntToStr(IDNODE);
    rs:=Connection.Execute(SQLStr);
    if RS.RecordCount>0 then
    begin
      rs.MoveFirst;
      while not RS.EOF do
      begin
        tmpint:=Integer(RS.Fields.Item[ID].Value);
        AddTreeNode(TmpTN,TmpInt);
        RS.MoveNext;
      end;
    end;
    //tmptn:=TTreeNode.Create();

  end;
end;

procedure TCatSystem.CreateNewCat(NewCatName: string;ParentID:Integer);
var
  SQLStr:string;
begin
  if Connection.Connected=False then
  begin
    NotConnected;
    Exit;
  end;
  SQLStr:='INSERT INTO ' + CatTableName + ' (' + CatName + ', ' +
  CatParent + ') VALUES (' + QuotedStr(NewCatName) + ', ' +
  QuotedStr(IntToStr(ParentID)) + ')';
  Connection.Execute(SQLStr);
  if TV<>nil then
  begin
    TV.Items.AddChild(GetTreeNodeByID(ParentID),NewCatName);
  end;
end;

procedure TCatSystem.DeleteCatByID(CatID: integer);
var
  RS:_Recordset;
  SQLStr:string;
  TmpInt:integer;
  I:Integer;
begin
  if CatID=RootCat then
  begin
    Exit;
  end;
  if Connection.Connected=False then
  begin
    NotConnected;
    Exit;
  end;
  sqlstr:='SELECT ' + ID + ' FROM ' + CatTableName +
  ' WHERE ' + CatParent + '=' + IntToStr(CatID);
  rs:=Connection.Execute(SQLStr);
  if rs.RecordCount>0 then
  begin
    rs.MoveFirst;
    while not rs.EOF do
    begin
      TmpInt:=Integer(RS.Fields[0].Value);
      DeleteCatByID(TmpInt);
      rs.MoveNext;
    end;
  end;
  if TV<>nil then TV.Items.Delete(GetTreeNodeByID(CatID));
  SQLStr:='DELETE FROM ' + CatTableName + ' WHERE ' + ID + '=' + IntToStr(CatID);
  Connection.Execute(SQLStr);
end;

procedure TCatSystem.FeelingTree;
begin
  if Connection.Connected=False then
  begin
    NotConnected;
    Exit;
  end;
  if TV<>nil then
  begin
    TV.Items.Clear;
    AddTreeNode(nil,RootCat);
  end;
end;

function TCatSystem.GetCatNameByID(CatID: Integer): string;
var
  SQLStr:string;
  RS:_Recordset;
begin
  if Connection.Connected=False then
  begin
    NotConnected;
    Exit;
  end;
  result:='';
  SQLStr:='SELECT ' + CatName + ' FROM ' + CatTableName + ' WHERE ' + ID + '=' + IntToStr(CatID);
  rs:=Connection.Execute(SQLStr);
  if rs.RecordCount=1 then
  begin
    result:=VarToStr(RS.Fields[0].Value);
  end;
end;

function TCatSystem.GetChildsIDs(CatID: Integer): TStringList;
var
  SQLStr:string;
  RS:_Recordset;
begin
  if Connection.Connected=False then
  begin
    NotConnected;
    Exit;
  end;
  SQLstr:='SELECT ' + ID + ' FROM ' + CatTableName + ' WHERE ' +
  CatParent + '=' + IntToStr(CatID);
  rs:=Connection.Execute(SQLStr);
  if RS.RecordCount>0 then
  begin
    RS.MoveFirst;
    while not rs.EOF do
    begin
      Result.Add(RS.Fields[0].Value);
    end;
  end;
end;

function TCatSystem.GetTreeNodeByID(CatID: Integer): TTreeNode;
var
  i:Integer;
  TmpInt:Integer;
begin
  if Connection.Connected=False then
  begin
    NotConnected;
    Exit;
  end;
  result:=nil;
  for i:=0 to TV.Items.Count-1 do
  begin
    tmpint:=Integer(tv.Items.Item[i].Data);
    if CatID=TmpInt then
    begin
      result:=tv.Items.Item[i];
      Break;
    end;
  end;
end;

function TCatSystem.HasChilds(CatID: Integer): Boolean;
var
  RS:_Recordset;
  SQLStr:string;
begin
  if Connection.Connected=False then
  begin
    NotConnected;
    Exit;
  end;
  SQLStr:='SELECT Count(' + ID + ') FROM ' + CatTableName + ' WHERE ' +
  CatParent + '=' + IntToStr(CatID);
  rs:=Connection.Execute(SQLStr);
  if Integer(rs.Fields[0].Value)<>0 then result:=True else result:=False;
end;

procedure TCatSystem.NotConnected;
begin
  MessageDlg('Íåò ïîäêëþ÷åíèÿ!',mtError,[mbOK],0);
end;

procedure TCatSystem.RenameCatByID(CatID: Integer; NewName: string);
var
  SQLStr:string;
begin
  if Connection.Connected=False then
  begin
    NotConnected;
    Exit;
  end;
  SQLStr:='UPDATE ' + CatTableName + ' SET ' + CatName + '=' + NewName +
  ' WHERE ' + ID + '=' + IntToStr(CatID);
  Connection.Execute(SQLStr);
  if TV<>nil then
  begin
    GetTreeNodeByID(CatID).Text:=NewName;
  end;
end;

end.