jsTreeView and jsSysTreeView Design and Description
The following is a brief description of basic overall operation and
design of the jsTreeView dBL class. Because the jsSysTreeView class is a
subclass of the jsTreeView class, this description also applies to the
jsSysTreeView class. Don't worry if you don't clearly
understand what is described. Simply read it for purposes of 'awareness'.
Much of the following will become clearer as you become familiar with
using jsTreeView. In reality, jsTreeView is quite simple to use. What
follows is a small attempt to satisfy those who want to know 'just a bit more'.
jsTreeView is a subclass of the stock TreeView dBL class. It can be placed on
a Form, a SubForm, a Container, or a NoteBook.
At runtime, a jsTreeView object will function the same as the stock TreeView.
None of the default stock TreeView operation has been changed. jsTreeView
simply adds functionality that does not exist in the stock TreeView.
Like most of the visual UI classes in the core product, the TreeView class in
the core product is not created by the core product. Rather, it is surfaced by
the core product from the operating system. dBASE simply 'surfaces' the
TreeView in a manner that is compatible and consistent with the dBL language.
The additional functionality of the jsTreeView class is achieved through the
operating system's API in the same way that dBASE itself talks to the API to
create a TreeView and surface the dBL access through the stock TreeView class.
jsTreeView simply uses API functionality to surface additional items that have
not been exploited by the core product.
The TreeView window is a message-based window rather than a
function-based window. Almost all functionality is
implemented via messages sent to the TreeView window. Some of
these messages use complex data structures to pass information to and from
the TreeView window. The jsTreeView class implements methods
(functions) which provide dBL access to the messages and structures. Each
method encapsulates a specific message supported by the TreeView
window by creating and filling any necessary data structures, sending
the appropriate message to the TreeView window, and by retrieving
any returned data as necessary from the associated data structures.
Don't let the discussion here regarding API, structures, and messages scare you
away. jsTreeView makes it easy to extend TreeView functionality in dBL
application code without needing to know how to work with structures or talk to
any API. jsTreeView bridges the gap between the application dBL code and the
TreeView window via the windows API. Through a few added methods, the advanced
functionality of the jsTreeView class can be directly
exploited using relatively simple dBL application code.
Because the jsTreeView class is, in the most simple definition, a dBL
'wrapper' for the operating system's TreeView window class, the most
authoritative resource for information regarding TreeView technology,
operation, and reference can be found at MSDN online under
Individual Control Reference.
Also, be sure to search MSDN for other information and examples of
using the TreeView.
But most of all, be sure to read the remaining jsTreeView documentation.
And review the dBL sample forms included with the jsTreeView package to
become more familiar with how jsTreeView can be used in dBL applications.