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gTreeView

Definition: include xpGUI.e

gdx tree_view = gTreeView([sequence tree_nodes={},] [rtn branchopen=NULL, ] string attributes="", dword_seq args={})
Description: Creates a nested tree control with expandable/collapsable nodes from a simple [recursive] data structure.

tree_nodes: a nested construct of the form {"text"[,attr][,children]}, suitable for passing to gTreeAddNodes().
branchopen: optional routine for deferred loading of sub-tree nodes, see BRANCHOPEN.
For more information on the attributes and args parameters see gSetAttributes().
This is a paranormalised function. (see technicalia)

The tree_nodes parameter may be empty, or omitted on creation and set via gTreeAddNodes() at some later time.

At the time of writing, few treeview attributes are supported, but in time I expect it will cope with at least EXPANDNODE, CONTRACTNODE, FOCUSNODE, TOPITEM, VISIBLENODE, as well as having a few more handler routines, probably.

Returns: the identifier of the created element.
pwa/p2js: Supported.
See Also: gTreeAddNodes
Example: 
-- demo\xpGUI\gTreeView.exw
include xpGUI.e
constant tree_nodes = {"Figures",               -- (branch with 5 children)
                       {"Other",                -- (leaf)
                        {"triangle",            -- (branch with 3 children)
                         {"STATE","COLLAPSED"},
                         {"equilateral",
                          {"isoceles",          -- (branch with 2 children)
                           {"STATE","COLLAPSED"},
                           {"acute",
                            "obtuse"}},
                          "scalenus"}
                        },
                        {"parallelogram",       -- (branch with 2 children)
                         {"square",             -- (should be open on load)
                          "diamond"}},
                        "2D",                   -- (leaf)
                        {"3D",                  -- (branch)
                         {"STATE","COLLAPSED"}, -- (needed here)
                         {}},                   -- (empty)
                        {"4D",
                         {"STATE","COLLAPSED"},
                         {"some",
                          "other",
                          "branch"},
                         {"random data"} -- (iff attr and children present)
                        }
                       }
                      }

gdx tree_view = gTreeView(tree_nodes),
    dlg = gDialog(tree_view,`gTreeView`)
gShow(dlg)
gMainLoop()
gTreeView
(note: that looks slightly different under GTK[3])

See also gTreeAddNodes for a more details of the structures, splitting/flattening them, and deferred loading.
Attributes:
Also: ACTIVE, CANFOCUS, FONT, EXPAND, MINSIZE, MAXSIZE, SIZE, TIP, VISIBLE.
Handlers:
BRANCHOPEN Event generated when a branch is expanded, and intended for implementing deferred (sub-tree) loading.

procedure branchopen(object treenode)

treenode: opaque/backend-specific, suitable for passing directly to gTreeGetUserId() and gTreeAddNodes().
Currently under GTK it is {treeview,iter,path}, under WinAPI it is {treeview,TreeIdx}, and under p2js it is a HTMLUListElement: you may be able to do a few dirty little debug tricks with it, but should cease and desist from doing anything like that in the finished code, plus those details may well change in a future release.

Should you not want a user to open a branch, simply don’t put any children in there in the first place.

Deferred loading is not worthwhile for a tree the size of the one shown above, but it certainly would be when loading a hard drive (for instance, try right clicking on C:\Windows, select Properties, and watch it start counting, then imagine staring at a blank screen until it finishes) or perhaps a database containing several decades-worth of detailed historical information.

The gTreeAddNodes example showcases deferred loading, however you are free to replace "tree_data" with anything you like[/can massage into the right format], including a database or even an (ideally asynchronous) remote fetch that triggers that code (in the main thread) when it completes.
also KEY: All common handlers are supported.
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