Back and Forward on a device: match history entries by component id

Opening a sheet on a device rebuilds the DOM, so every element is new and
the history, which matched by identity, pruned each sheet as soon as it was
recorded. On a device entries now match by id, and Back reopens a view on
the current element rather than the snapshot it was recorded with.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app_state.py

@@ -8,7 +8,7 @@ so later rebinding would only ever be seen by the module that did it.
 import configparser
 import os
 
-VERSION = "0.0.0.157"
+VERSION = "0.0.0.160"
 PROPERTIES_FILE = os.path.join(os.path.dirname(os.path.abspath(__file__)), "editor.properties")
 DEFAULT_GRID_SIZE = 10
 DEFAULT_ADD_TIMESTAMP = True

main.py

@@ -80,7 +80,7 @@ DEFAULT_WINDOW_HEIGHT = 600
 # them; the cap only stops an unbounded list.
 HISTORY_LIMIT = 50
 
-# What a history entry can be showing. The editor pane holds one of these three at a
+# What a history entry can be showing. The editor pane holds one of these five at a
 # time, so the history that walks it has to be able to name each of them.
 VIEW_SHEET = "sheet"
 VIEW_PROPERTIES = "properties"
@@ -103,8 +103,10 @@ MENU_FORWARD_LABEL = "Forward"
 #                               file's root node
 #   (VIEW_PROPERTIES, comp)     the Properties view of that component
 #   (VIEW_LINKS, comp)          the Link View of that component
+#   (VIEW_PAGE, comp)           the oxPage view of that page component
+#   (VIEW_USERS, comp)          the User Manager of that UserService component
 #
-# Opening a Properties or Link view is a move like opening a sheet, so Back from one
+# Opening any of these views is a move like opening a sheet, so Back from one
 # lands on what the pane showed before it rather than skipping past to the sheet before
 # that, and Forward brings it back.
 #
@@ -903,6 +905,18 @@ def on_canvas_wheel_zoom(event):
     return "break"
 
 
+def on_canvas_wheel_scroll(event):
+    """Plain wheel pans the sheet up and down, Shift + wheel pans it sideways."""
+    if not event.delta:
+        return "break"
+    units = -1 if event.delta > 0 else 1
+    if event.state & 0x0001:
+        canvas.xview_scroll(units, "units")
+    else:
+        canvas.yview_scroll(units, "units")
+    return "break"
+
+
 # --- Event handlers ---
 
 def on_tree_select(event):
@@ -2010,6 +2024,37 @@ def _sync_pane_toggle_button():
 
 # --- Sheet view history ---
 
+def _same_element(a, b):
+    """Whether two history elements name the same component.
+
+    In a file that is identity. On a device every sheet opened rebuilds the DOM from the
+    device, handing out fresh elements for the same components, so there it is the id.
+    """
+    if a is b:
+        return True
+    if a is None or b is None or not app_state.live_mode:
+        return False
+    a_id = a.get("id")
+    return a_id is not None and a_id == b.get("id")
+
+
+def _current_element(element):
+    """The element in the DOM now that names the same component as this one.
+
+    Only a device swaps elements out from under the history; in a file, or when nothing
+    by that id is left, the element comes back as it was.
+    """
+    if element is None or not app_state.live_mode:
+        return element
+    root = app_state.xml_root_element
+    if root is None:
+        return element
+    for candidate in root.iter():
+        if _same_element(candidate, element):
+            return candidate
+    return element
+
+
 def _tree_item_for_element(element):
     """The tree item whose sheet is this element's children, or None if it is gone.
 
@@ -2024,7 +2069,7 @@ def _tree_item_for_element(element):
         children = tree.get_children()
         return children[0] if children else None
     for item_id, mapped in app_state.tree_element_map.items():
-        if mapped is element:
+        if _same_element(mapped, element):
             return item_id
     return None
 
@@ -2056,7 +2101,7 @@ def _prune_view_history():
         # and a Back that visibly does nothing is worse than a shorter trail. The
         # position still lands on whichever of the two it was on, since they are the
         # same view either way.
-        if kept and kept[-1][0] == entry[0] and kept[-1][1] is entry[1]:
+        if kept and kept[-1][0] == entry[0] and _same_element(kept[-1][1], entry[1]):
             if position <= history_index:
                 new_index = len(kept) - 1
             continue
@@ -2120,11 +2165,12 @@ def record_visit(kind, element):
         view_history.clear()
         history_index = -1
 
-    # Opening what is already on screen is not a move. Compared by identity, since two
-    # sheets are the same sheet only when they are the same element.
+    # Opening what is already on screen is not a move. Compared by identity in a file,
+    # where two sheets are the same sheet only when they are the same element, and by id
+    # on a device, where each sheet opened hands out fresh elements.
     if 0 <= history_index < len(view_history):
         current_kind, current_element = view_history[history_index]
-        if current_kind == kind and current_element is element:
+        if current_kind == kind and _same_element(current_element, element):
             return
 
     del view_history[history_index + 1:]
@@ -2147,6 +2193,11 @@ def _show_history_entry(position):
     if not _entry_is_reachable((kind, element)):
         return
 
+    # On a device the entry may hold an element from an earlier rebuild; a panel built on
+    # that would show the values of that moment, not the device's.
+    element = _current_element(element)
+    view_history[position] = (kind, element)
+
     _suppress_history = True
     try:
         if kind == VIEW_SHEET:
@@ -3364,6 +3415,12 @@ canvas.bind("<Double-1>", on_canvas_double_click)
 canvas.bind("<Control-MouseWheel>", on_canvas_wheel_zoom)
 canvas.bind("<Control-Button-4>", do_zoom_in)
 canvas.bind("<Control-Button-5>", do_zoom_out)
+canvas.bind("<MouseWheel>", on_canvas_wheel_scroll)
+canvas.bind("<Shift-MouseWheel>", on_canvas_wheel_scroll)
+canvas.bind("<Button-4>", lambda e: canvas.yview_scroll(-1, "units"))
+canvas.bind("<Button-5>", lambda e: canvas.yview_scroll(1, "units"))
+canvas.bind("<Shift-Button-4>", lambda e: canvas.xview_scroll(-1, "units"))
+canvas.bind("<Shift-Button-5>", lambda e: canvas.xview_scroll(1, "units"))
 
 paned_window.add(frame_editor, weight=3)