Delete a Treeview node

Peter Kiers
Peter Kiers used Ask the Experts™
on
Dear Experts,

I have made a little programm that has a Treeview, a RichEdit.
and 4 buttons on a Panel. 2 buttons are for loading and saving
the treeview nodes with its associating text on the RichtEdit
to a database. The other 2 buttons are for creating a Folder-node
and a File-node in the Treeview. Everything works perfect.

Now I want to make a fifth button on the panel for deleting
a Treeview node. The procedure is done:

procedure TForm1.DeleteItemClick(Sender: TObject);
var
   node : TTreeNode;
   mess, str : string;
   key_stat : integer;
begin
    Node := Treeview.Selected;
    if Assigned(Node) then
       begin
       str := Node.Text;
       mess := 'Are you sure that you want to delete the';
       Case Node.Level of
         0 : mess := mess + ' folder : ' +#13+#13 + str + '   ???' +#13+
                    'All folders, subfolders, items and subitems' +#13+ 'will be permanently deleted !!' +#13;
         1 : mess := mess + ' item : ' +#13+#13 + str + '   ???' + #13;
       end;
       with Application do
         begin
         NormalizeTopMosts;
         key_stat := MessageBox(pchar(mess), '         Confirmation', MB_YESNO);
         RestoreTopMosts;
       end;
       if key_stat = 7 then  Exit;         // 6 - YES ; 7 - N0
       TreeView.Items.Delete(Treeview.Selected);
       end
    else ShowMessage('Select a folder in the treeview first.');
end;

ACCEPT for one thing: The deleted node is still available in the database!!!
And it should be erased too. That's because the DeleteItemClick should call
for this procedure:

procedure TItem.Delete;
begin
//
end;

I have put the whole unit in the code-section.
Who can help me?

Greetings, Peter Kiers

unit Unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, DB, ADODB, ComCtrls, StdCtrls, ImgList, ExtCtrls;
 
type
  TForm1 = class(TForm)
    TreeView1: TTreeView;
    Splitter1: TSplitter;
    Panel1: TPanel;
    Button1: TButton;
    Button2: TButton;
    ADOQuery1: TADOQuery;
    ADOConnection1: TADOConnection;
    FolderBtn: TButton;
    FileBtn: TButton;
    ImageList1: TImageList;
    RichEdit1: TRichEdit;
    Button3: TButton;
    procedure Button3Click(Sender: TObject);
    procedure RichEdit1KeyUp(Sender: TObject; var Key: Word;
      Shift: TShiftState);
    procedure FolderBtnClick(Sender: TObject);
    procedure FileBtnClick(Sender: TObject);
    procedure TreeView1Change(Sender: TObject; Node: TTreeNode);
    procedure FormCreate(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    
  private
    { Private declarations }
    procedure savetree(t: ttreeview);
    procedure loadtree(t: TTreeView);
    procedure saveNode(n: TTreeNode);
    function findNode(t:TTreeView; id: integer): TTreeNode;
    procedure AddItem(aText: string; aIndex: Integer; aParent: TTreeNode);
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
 
implementation
 
{$R *.dfm}
 
type
  TItem = class(TObject)
  private
    fStatus: byte;
    fParentID: integer;
    fNodeText: string;
    fID: integer;
    fData: string;
    fSaver: TAdoQuery;
    fChanged: Boolean;        
    fSaveImmediate: boolean;
    fIsNew: Boolean;
    fImageIndex: integer;
    procedure SetData(const Value: string);
    procedure SetNodeText(const Value: string);
    procedure SetParentID(const Value: integer);
    procedure SetStatus(const Value: byte);
    procedure SetImageIndex(const Value: integer);
  protected
    procedure Changed; dynamic;
  public
    constructor Create(aSaver: TAdoQuery; AId, AParentID: integer; AStatus: byte);
    constructor LoadFromDataset(aSaver: TAdoQuery);
    procedure BeginUpdate;
    procedure EndUpdate;
    procedure Delete;
    procedure Save;
  published
    property ID: integer read fID write fID;
    property ParentID: integer read fParentID write SetParentID;
    property ImageIndex: integer read fImageIndex write SetImageIndex;
    property Status: byte read FStatus write SetStatus;
    property Data: string read fData write SetData;
    property NodeText: string read fNodeText write SetNodeText;
  end;
 
{ TItem }
 
procedure TItem.BeginUpdate;
begin
  fSaveImmediate := false;                 
end;
(*---------------------------------------------------*)
procedure TItem.Changed;
begin
  fChanged := True;
  if fSaveImmediate then Save;
end;
(*---------------------------------------------------*)
constructor TItem.Create(aSaver: TAdoQuery; AId, AParentID: integer;
  AStatus: byte);
begin
  inherited Create;
  fChanged := False;
  fSaveImmediate := True;
  fIsNew := True;
  fSaver := aSaver;
  fID := AID;
  fParentID := AParentID;
  fStatus := AStatus;
  fNodeText := '';
  fData := '';
end;
(*---------------------------------------------------*)
procedure TItem.Delete;
begin
//
end;
(*---------------------------------------------------*)
procedure TItem.EndUpdate;
begin
  fSaveImmediate := True;
  if fChanged then Save;
end;
(*---------------------------------------------------*)
constructor TItem.LoadFromDataset(aSaver: TAdoQuery);
begin
  Create(aSaver, 0, 0, 0);
  if not aSaver.IsEmpty then
  begin
    fId := aSaver.FieldByName('ID').AsInteger;
    fParentID := aSaver.FieldByName('PARENT').AsInteger;
    fStatus := aSaver.FieldByName('STATUS').AsInteger;
    fNodeText := aSaver.FieldByName('NAME').AsString;
    if aSaver.FindField('DATA') <> nil then
      fData := aSaver.FieldByName('DATA').AsString;
    fImageIndex := aSaver.FieldByName('IMAGE_INDEX').AsInteger;
    fIsNew := False;
  end;
end;
(*---------------------------------------------------*)
procedure TItem.Save;
begin
  if fIsNew then
    fSaver.SQL.Text :=
      'insert into tree (parent, name, status, image_index, data) values (:v1, :v2, :v3, :v4, :v5)'
  else
    fSaver.SQL.Text :=
      'update tree set parent = :v1, name = :v2, status = :v3, image_index = :v4, data = :v5 where id = :v6';
  fSaver.Parameters.ParamByName('v1').Value := fparentID;
  fSaver.Parameters.ParamByName('v2').Value := fNodeText;
  fSaver.Parameters.ParamByName('v3').Value := fStatus;
  fSaver.Parameters.ParamByName('v4').Value := fImageIndex;
  fSaver.Parameters.ParamByName('v5').Value := fData;
  if not fIsNew then
    fSaver.Parameters.ParamByName('v6').Value := fId;
  fSaver.ExecSQL;
  if fIsNew then
  begin
    fSaver.SQL.Text :=
      'SELECT id from tree order by id desc';
    fSaver.Open;
    fId := fSaver.FieldByName('ID').asInteger;
    fSaver.Close;
    fIsNew := False;
  end;
  fChanged := False;
end;
(*---------------------------------------------------*)
procedure TItem.SetData(const Value: string);
begin
  if fData <> Value then
  begin
    fData := Value;
    Changed;
  end;
end;
(*---------------------------------------------------*)
procedure TItem.SetImageIndex(const Value: integer);
begin
  if fImageIndex <> Value then
  begin
    fImageIndex := Value;
    Changed;
  end;
end;
(*---------------------------------------------------*)
procedure TItem.SetNodeText(const Value: string);
begin
  if fNodeText <> Value then
  begin
    fNodeText := Value;
    Changed;
  end;
end;
(*---------------------------------------------------*)
procedure TItem.SetParentID(const Value: integer);
begin
  if fParentId <> Value then
  begin
    fParentID := Value;
    Changed;
  end;
end;
(*---------------------------------------------------*)
procedure TItem.SetStatus(const Value: byte);
begin
  if fStatus <> Value then
  begin
    FStatus := Value;
    Changed;
  end;
end;
(*---------------------------------------------------*)
procedure TForm1.AddItem(aText: string; aIndex: Integer; aParent: TTreeNode);
var n: TTreeNode;
  data: TItem;
  parentId: integer;
begin
  parentId := 0;
  if (aParent <> nil) and (TItem(aParent.Data) <> nil) then
    parentId := TItem(aParent.Data).ID;
  data := TItem.Create(AdoQuery1, -1, parentId, 0);
  data.NodeText := aText;
  data.ImageIndex := aIndex;
  n := TTreeNode.Create(TreeView1.Items);
  n.Text := data.NodeText;
  n.ImageIndex := data.ImageIndex;
  n.SelectedIndex := data.ImageIndex;
  TreeView1.Items.AddNode(n, aParent, aText, data, naAddChild);
end;
(*---------------------------------------------------*)
procedure TForm1.Button1Click(Sender: TObject);
begin
  loadTree(treeview1);
end;
(*---------------------------------------------------*)
procedure TForm1.Button2Click(Sender: TObject);
begin
  savetree(treeview1);
end;
procedure TForm1.Button3Click(Sender: TObject);
var
   node : TTreeNode;
   mess, str : string;
   key_stat : integer;
begin
    Node := Treeview1.Selected;
    if Assigned(Node) then
       begin
       str := Node.Text;
       mess := 'Are you sure that you want to delete the';
       Case Node.Level of
         0 : mess := mess + ' folder : ' +#13+#13 + str + '   ???' +#13+
                    'All folders, subfolders, items and subitems' +#13+ 'will be permanently deleted !!' +#13;
         1 : mess := mess + ' item : ' +#13+#13 + str + '   ???' + #13;
       end;
       with Application do
         begin
         NormalizeTopMosts;
         key_stat := MessageBox(pchar(mess), '         Confirmation', MB_YESNO);
         RestoreTopMosts;
       end;
       if key_stat = 7 then  Exit;         // 6 - YES ; 7 - N0
       TreeView1.Items.Delete(Treeview1.Selected);
       end
    else ShowMessage('Select a folder in the treeview first.');
end;
(*---------------------------------------------------*)
procedure TForm1.FileBtnClick(Sender: TObject);
var aText: string;
begin
  if (TreeView1.Selected <> nil) and (TreeView1.Selected.ImageIndex = 15) then
  begin
     if InputQuery('File', 'Enter a file name', aText) then
      AddItem(aText, 17, TreeView1.Selected);
  end else
    ShowMessage('Select a folder in the treeview first.');
end;
(*---------------------------------------------------*)
function TForm1.findNode(t: TTreeView; id: integer): TTreeNode;
var i:integer;
begin
  i:=0;
  while (i<t.items.count) and (TItem(t.items[i].data).ID<>id) do
    inc(i);
  if i<t.items.count then result:=t.items[i]
                     else result:=nil;
end;
(*---------------------------------------------------*)
procedure TForm1.FolderBtnClick(Sender: TObject);
var aText: string;
  aParent: TTreeNode;
begin
  aParent := nil;
  if TreeView1.Selected <> nil then
  begin
    if TreeView1.Selected.ImageIndex = 15 then
      aParent := TreeView1.Selected
    else
    begin
      ShowMessage('Select a folder first');
      Exit;
    end;
  end;
  if InputQuery('Folder', 'Enter a folder name', aText) then
    AddItem(aText, 15, aParent);
end;
(*---------------------------------------------------*)
procedure TForm1.FormCreate(Sender: TObject);
var
  conn_str:string;
begin
  conn_str:='provider=Microsoft.Jet.OLEDB.4.0;Persist Security Info=False;Data Source=';
  conn_str:=conn_str+IncludeTrailingPathDelimiter(ExtractFilePath(Application.Exename));
  conn_str:=conn_str+'test.pkd;';
  ADOConnection1.Connected:=False;
  ADOConnection1.ConnectionString:=conn_str;
  ADOConnection1.Connected:=True;
  ADOConnection1.Open;
end;
(*---------------------------------------------------*)
procedure TForm1.loadtree(t: TTreeView);
var
  p, n: TTreeNode;
  data: TItem;
begin
  t.Items.Clear;
  ADOQuery1.SQL.Text := 'select * from tree order by parent asc';
  ADoQuery1.Open;
  while not ADoQuery1.Eof do
  begin
    data := TItem.LoadFromDataset(AdoQuery1);
    p := FindNode(t, data.ParentID);
    n := t.items.AddChildObject(p, data.NodeText, data);
    n.ImageIndex := data.ImageIndex;
    n.SelectedIndex := data.ImageIndex;
    AdoQuery1.Next;
  end;
  AdoQuery1.Close;
end;
(*---------------------------------------------------*)
procedure TForm1.saveNode(n: TTreeNode);
var i, aParent: integer;
  item: TItem;
begin
  item := TItem(n.Data);
  if item <> nil then
  begin
    item.BeginUpdate;
    try
      Item.NodeText := n.Text;
      aParent := 0;
      if (n.Parent <> nil) and (TItem(n.Parent.Data) <> nil) then
        aParent := TItem(n.Parent.Data).ID;
      Item.ParentID := aParent;
      Item.ImageIndex := n.ImageIndex;
    finally
      Item.EndUpdate;
    end;
  end;
  for i := 0 to n.Count-1 do SaveNode(n.Item[i]);
end;
(*---------------------------------------------------*)
procedure TForm1.savetree(t: ttreeview);
var n: TTreeNode;
begin
  n := t.items.getFirstNode;
  while n <> nil do
  begin
    SaveNode(n);
    n := n.getNextSibling;
  end;
end;
(*---------------------------------------------------*)
procedure TForm1.TreeView1Change(Sender: TObject; Node: TTreeNode);
begin
  RichEdit1.Text := '';
  if (Node <> nil) and (Node.ImageIndex = 15) then
    RichEdit1.Text := TItem(Node.Data).Data;
end;
(*---------------------------------------------------*)
procedure TForm1.RichEdit1KeyUp(Sender: TObject; var Key: Word;
  Shift: TShiftState);
  var n: TTreeNode;
begin
        n := TreeView1.Selected;
        if (n <> nil) and (n.ImageIndex = 15) then
        begin
        TItem(n.Data).fSaveImmediate := False;
         TItem(N.Data).Data := RichEdit1.Text;
         end;
end;
(*---------------------------------------------------*)
end.

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Commented:
It really depends on the design approach you are taking.  One approach is to allow the user to do any and all editing they want, then they hit save if they want to save it or cancel if they want to undo all of the changes.  It sounds like you are going for a bit more of a live editing situation where there should be no need for hitting save, everything happens right when you do it.

If the latter situation is what you are looking for, try this.  I threw together a quick example of sub-classing the TTreeNode so you will be notified when the items are deleted.  This keeps things simple on your end in that you do not need to do all of the nested calls to delete all possible children.  You would simply store your ID for each record in the object you create.  Then, when the time comes to delete the associated database records, your OnBeforeDelete method will be called with the object being deleted so you will have all of the information needed to delete the items one at a time from the database.  All I put on the form was a tree view and a button.  I tied the forms OnCreate and the Button's OnClick.  Within the form create I create an example tree structure that you can see on the tree view.  When you click the delete on the main item you will see the OnBeforeDelete gets called for all three items.

Let me know if this would work for you.
unit Unit3;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ComCtrls;
 
type
  TForm3 = class(TForm)
    TreeView1: TTreeView;
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
    procedure TreeViewBeforeDelete(Sender : TObject);
  public
    { Public declarations }
  end;
 
  TMyTreeNode = class(TTreeNode)
  private
    fOnBeforeDelete: TNotifyEvent;
    procedure BeforeDelete;
  protected
  public
    ID : integer;
 
    destructor Destroy; override;
 
    property OnBeforeDelete : TNotifyEvent
      read fOnBeforeDelete
      write fOnBeforeDelete;
  end;
 
var
  Form3: TForm3;
 
implementation
 
{$R *.dfm}
 
procedure TForm3.Button1Click(Sender: TObject);
begin
  if Assigned(TreeView1.Selected) then
    TreeView1.Items.Delete(TMyTreeNode(TreeView1.Selected));
end;
 
procedure TForm3.FormCreate(Sender: TObject);
var
  NewNode : TTreeNode;
  MyTreeNode : TMyTreeNode;
  ParentNode : TMyTreeNode;
 
begin
  ParentNode := nil;
  MyTreeNode := TMyTreeNode.Create(TreeView1.Items);
  MyTreeNode.OnBeforeDelete := TreeViewBeforeDelete;
  TreeView1.Items.AddNode(MyTreeNode, ParentNode, 'Line One', nil, naAdd);
 
  ParentNode := MyTreeNode;
  MyTreeNode := TMyTreeNode.Create(TreeView1.Items);
  MyTreeNode.OnBeforeDelete := TreeViewBeforeDelete;
  TreeView1.Items.AddNode(MyTreeNode, ParentNode, 'Line One A', nil, naAddChild);
 
  ParentNode := MyTreeNode;
  MyTreeNode := TMyTreeNode.Create(TreeView1.Items);
  MyTreeNode.OnBeforeDelete := TreeViewBeforeDelete;
  TreeView1.Items.AddNode(MyTreeNode, ParentNode, 'Line One A-1', nil, naAddChild);
end;
 
procedure TForm3.TreeViewBeforeDelete(Sender: TObject);
begin
  //breakpoint here to see it stop on each deleted item.
  //place code here for database deletions.
  //Check that Sender is the correct type, then type cast it to
  //get values.
end;
 
{ TMyTreeNode }
 
procedure TMyTreeNode.BeforeDelete;
begin
  if Assigned(fOnBeforeDelete) then
    fOnBeforeDelete(Self);
end;
 
destructor TMyTreeNode.Destroy;
begin
  BeforeDelete;
 
  inherited;
end;
 
end.

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Peter KiersOperator

Author

Commented:
Thanks
P.

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