If you have studied the ListView control you will find the TreeView similar and even more flexible and powerful. The TreeView control provides a 'tree' view of data, identical in scope to Windows Explorer, with nodes and sub-nodes and icons to represent collapsed and expanded nodes. The default icons are the '+' and '-' symbols, which should be adequate for many purposes.
You have probably come across the idea of binary trees and graphical trees defined recursively in Logo. Well, trees in a TreeView are not like these, they use similar terminology and have a branching structure but they are not balanced in construction or appearance. Instead they are more linear in appearance with any number of items at any level. Nevertheless, they are tree-like and they have their uses for data of a branching nature.
As with the ListView the control provides an editor for setting up trees for viewing at run-time (right-click the control in the form):
The TreeView has file load and save operations so an application can be created with this functionality. A file for a TreeView can be a simple text file with tabs for indents within it:
The Special Magic of Ella and Louis
Don't Be That Way
Goodman-Parish-Sampson
They All Laughed
Gershwin
Autumn in New York
Duke
Stompin At The Savoy
Goodman-Webb-Sampson
I Won't Dance
Kern-Fields-McHugh-Harbach-Hammerstein
II
Getz and Gilberto...
Functionality similar to the ListView example has been built into this application:
An ImageList has been added
The code for the Add Node button is:
procedure TForm1.Button1Click(Sender: TObject);
begin
treeview1.Items.add(nil, edit1.text)
end;
The code for the Add SubNode button is:
procedure TForm1.Button2Click(Sender: TObject);
var node:TTreenode;
begin
node := treeview1.Selected;
if node <>nil then
Treeview1.items.addchild(node, edit2.Text)
else showmessage ('No node is selected');
end;
The code for the Delete Node button is:
procedure TForm1.Button3Click(Sender: TObject);
var node:TTreenode;
begin
node:=treeview1.Selected;
if node <> nil then
treeview1.Items.Delete(node)
else
showmessage ('No node is selected');
end;
The code to open a file for a TreeView is more straightforward than that for a ListView:
procedure TForm1.Open1Click(Sender: TObject);
begin
if opendialog1.execute then
TreeView1.LoadFromFile(opendialog1.FileName);
end;
(But note that this does not include image information.) The code for the Save routine:
procedure TForm1.Save1Click(Sender: TObject);
begin
if savedialog1.execute then
treeview1.SaveToFile(savedialog1.FileName);
end;
The TreeView already has left mouse button click (select node) and double-click functionality (expands or contracts a node) but it does not have right-click functionality, so we can call the EditText procedure:
procedure TForm1.TreeView1MouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
begin
if button = mbRight then
if treeview1.Selected <> nil then
if button=mbRight then
treeview1.Selected.EditText;
end;
