Add set_elements method to ListBox widget

Introduced a new `set_elements` method in the ListBox widget to handle initialization and validation of list items and dimensions. This method simplifies listbox element updates and ensures proper scrolling when the list exceeds display limits.

gui/widgets/listbox.py

@@ -68,9 +68,34 @@ class Listbox(Widget):
         self.cb_args = args
         self.select_color = select_color
         self.fontcolor = fontcolor
-        self._value = value # No callback until user selects
+        self._value = value  # No callback until user selects
         self.ev = value  # Value change detection
 
+
+    def set_elements(self, new_elements):
+        e0 = new_elements[0]
+        # Check whether elements specified as (str, str,...) or ([str, callback, args], [...)
+        if isinstance(e0, tuple) or isinstance(e0, list):
+            self.els = new_elements  # Retain original for .despatch
+            self.elements = [x[0] for x in new_elements]  # Copy text component
+        else:
+            # elements are strings list
+            self.elements = new_elements
+
+        if any(not isinstance(s, str) for s in self.elements):
+            raise ValueError("Invalid elements arg.")
+
+        # Calculate dimensions
+        self.entry_height, height, self.dlines, tw = self.dimensions(
+            self.writer, self.elements, self.dlines
+        )
+        self.ntop = 0
+        if self._value >= self.dlines:  # Must scroll
+            self._value = min(self._value, len(new_elements) - 1)
+            self.ntop = self._value - self.dlines + 1
+
+        self.draw = True
+
     def show(self):
         if not super().show(False):  # Clear to self.bgcolor
             return