feat: add ListView.build_controls_on_demand property for optional o…

…n-demand building of controls (#4751)

* initial commit

* reorder ListTile props

packages/flet/lib/src/controls/list_view.dart

@@ -52,22 +52,27 @@ class _ListViewControlState extends State<ListViewControl> {
     bool? adaptive =
         widget.control.attrBool("adaptive") ?? widget.parentAdaptive;
 
-    final horizontal = widget.control.attrBool("horizontal", false)!;
-    final spacing = widget.control.attrDouble("spacing", 0)!;
-    final dividerThickness = widget.control.attrDouble("dividerThickness", 0)!;
-    final itemExtent = widget.control.attrDouble("itemExtent");
-    final cacheExtent = widget.control.attrDouble("cacheExtent");
-    final semanticChildCount = widget.control.attrInt("semanticChildCount");
-    final firstItemPrototype =
+    var horizontal = widget.control.attrBool("horizontal", false)!;
+    var spacing = widget.control.attrDouble("spacing", 0)!;
+    var dividerThickness = widget.control.attrDouble("dividerThickness", 0)!;
+    var itemExtent = widget.control.attrDouble("itemExtent");
+    var cacheExtent = widget.control.attrDouble("cacheExtent");
+    var semanticChildCount = widget.control.attrInt("semanticChildCount");
+    var firstItemPrototype =
         widget.control.attrBool("firstItemPrototype", false)!;
-    final padding = parseEdgeInsets(widget.control, "padding");
-    final reverse = widget.control.attrBool("reverse", false)!;
+    var padding = parseEdgeInsets(widget.control, "padding");
+    var reverse = widget.control.attrBool("reverse", false)!;
     var clipBehavior =
         parseClip(widget.control.attrString("clipBehavior"), Clip.hardEdge)!;
 
-    List<Control> visibleControls =
-        widget.children.where((c) => c.isVisible).toList();
+    List<Control> ctrls = widget.children.where((c) => c.isVisible).toList();
     var scrollDirection = horizontal ? Axis.horizontal : Axis.vertical;
+    var buildControlsOnDemand =
+        widget.control.attrBool("buildControlsOnDemand", true)!;
+    var prototypeItem = firstItemPrototype && widget.children.isNotEmpty
+        ? createControl(widget.control, ctrls[0].id, disabled,
+            parentAdaptive: adaptive)
+        : null;
 
     Widget listView = LayoutBuilder(
       builder: (BuildContext context, BoxConstraints constraints) {
@@ -77,56 +82,68 @@ class _ListViewControlState extends State<ListViewControl> {
         var shrinkWrap =
             (!horizontal && constraints.maxHeight == double.infinity) ||
                 (horizontal && constraints.maxWidth == double.infinity);
-
-        Widget child = spacing > 0
-            ? ListView.separated(
+        Widget child = !buildControlsOnDemand
+            ? ListView(
                 controller: _controller,
                 cacheExtent: cacheExtent,
                 reverse: reverse,
                 clipBehavior: clipBehavior,
                 scrollDirection: scrollDirection,
                 shrinkWrap: shrinkWrap,
                 padding: padding,
-                itemCount: widget.children.length,
-                itemBuilder: (context, index) {
-                  return createControl(
-                      widget.control, visibleControls[index].id, disabled,
-                      parentAdaptive: adaptive);
-                },
-                separatorBuilder: (context, index) {
-                  return horizontal
-                      ? dividerThickness == 0
-                          ? SizedBox(width: spacing)
-                          : VerticalDivider(
-                              width: spacing, thickness: dividerThickness)
-                      : dividerThickness == 0
-                          ? SizedBox(height: spacing)
-                          : Divider(
-                              height: spacing, thickness: dividerThickness);
-                },
-              )
-            : ListView.builder(
-                controller: _controller,
-                clipBehavior: clipBehavior,
                 semanticChildCount: semanticChildCount,
-                reverse: reverse,
-                cacheExtent: cacheExtent,
-                scrollDirection: scrollDirection,
-                shrinkWrap: shrinkWrap,
-                padding: padding,
-                itemCount: widget.children.length,
                 itemExtent: itemExtent,
-                itemBuilder: (context, index) {
-                  return createControl(
-                      widget.control, visibleControls[index].id, disabled,
-                      parentAdaptive: adaptive);
-                },
-                prototypeItem: firstItemPrototype && widget.children.isNotEmpty
-                    ? createControl(
-                        widget.control, visibleControls[0].id, disabled,
-                        parentAdaptive: adaptive)
-                    : null,
-              );
+                children: ctrls
+                    .map((c) => createControl(widget.control, c.id, disabled,
+                        parentAdaptive: adaptive))
+                    .toList(),
+                prototypeItem: prototypeItem,
+              )
+            : spacing > 0
+                ? ListView.separated(
+                    controller: _controller,
+                    cacheExtent: cacheExtent,
+                    reverse: reverse,
+                    clipBehavior: clipBehavior,
+                    scrollDirection: scrollDirection,
+                    shrinkWrap: shrinkWrap,
+                    padding: padding,
+                    itemCount: widget.children.length,
+                    itemBuilder: (context, index) {
+                      return createControl(
+                          widget.control, ctrls[index].id, disabled,
+                          parentAdaptive: adaptive);
+                    },
+                    separatorBuilder: (context, index) {
+                      return horizontal
+                          ? dividerThickness == 0
+                              ? SizedBox(width: spacing)
+                              : VerticalDivider(
+                                  width: spacing, thickness: dividerThickness)
+                          : dividerThickness == 0
+                              ? SizedBox(height: spacing)
+                              : Divider(
+                                  height: spacing, thickness: dividerThickness);
+                    },
+                  )
+                : ListView.builder(
+                    controller: _controller,
+                    clipBehavior: clipBehavior,
+                    semanticChildCount: semanticChildCount,
+                    reverse: reverse,
+                    cacheExtent: cacheExtent,
+                    scrollDirection: scrollDirection,
+                    shrinkWrap: shrinkWrap,
+                    padding: padding,
+                    itemCount: widget.children.length,
+                    itemExtent: itemExtent,
+                    itemBuilder: (context, index) {
+                      return createControl(
+                          widget.control, ctrls[index].id, disabled,
+                          parentAdaptive: adaptive);
+                    },
+                    prototypeItem: prototypeItem,
+                  );
 
         child = ScrollableControl(
             control: widget.control,

sdk/python/packages/flet/src/flet/core/list_tile.py

@@ -82,15 +82,15 @@ def main(page):
 
     def __init__(
         self,
-        content_padding: Optional[PaddingValue] = None,
-        bgcolor: Optional[ColorValue] = None,
-        bgcolor_activated: Optional[str] = None,
-        hover_color: Optional[ColorValue] = None,
-        leading: Optional[Control] = None,
         title: Optional[Control] = None,
         subtitle: Optional[Control] = None,
-        trailing: Optional[Control] = None,
         is_three_line: Optional[bool] = None,
+        leading: Optional[Control] = None,
+        trailing: Optional[Control] = None,
+        content_padding: PaddingValue = None,
+        bgcolor: Optional[ColorValue] = None,
+        bgcolor_activated: Optional[str] = None,
+        hover_color: Optional[ColorValue] = None,
         selected: Optional[bool] = None,
         dense: Optional[bool] = None,
         autofocus: Optional[bool] = None,
@@ -114,8 +114,8 @@ def __init__(
         subtitle_text_style: Optional[TextStyle] = None,
         leading_and_trailing_text_style: Optional[TextStyle] = None,
         min_height: OptionalNumber = None,
-        on_click=None,
-        on_long_press=None,
+        on_click: OptionalControlEventCallable = None,
+        on_long_press: OptionalControlEventCallable = None,
         #
         # ConstrainedControl and AdaptiveControl
         #

sdk/python/packages/flet/src/flet/core/list_view.py

@@ -1,4 +1,4 @@
-from typing import Any, Callable, List, Optional, Sequence, Union
+from typing import Any, List, Optional, Sequence, Union
 
 from flet.core.adaptive_control import AdaptiveControl
 from flet.core.animation import AnimationValue
@@ -10,6 +10,7 @@
     ClipBehavior,
     OffsetValue,
     OptionalControlEventCallable,
+    OptionalEventCallable,
     PaddingValue,
     ResponsiveNumber,
     RotateValue,
@@ -68,13 +69,14 @@ def __init__(
         clip_behavior: Optional[ClipBehavior] = None,
         semantic_child_count: Optional[int] = None,
         cache_extent: OptionalNumber = None,
+        build_controls_on_demand: Optional[bool] = None,
         #
         # ScrollableControl specific
         #
         auto_scroll: Optional[bool] = None,
         reverse: Optional[bool] = None,
         on_scroll_interval: OptionalNumber = None,
-        on_scroll: Optional[Callable[[OnScrollEvent], None]] = None,
+        on_scroll: OptionalEventCallable[OnScrollEvent] = None,
         #
         # ConstrainedControl
         #
@@ -160,6 +162,7 @@ def __init__(
         self.clip_behavior = clip_behavior
         self.semantic_child_count = semantic_child_count
         self.cache_extent = cache_extent
+        self.build_controls_on_demand = build_controls_on_demand
 
     def _get_control_name(self):
         return "listview"
@@ -265,3 +268,12 @@ def semantic_child_count(self) -> Optional[int]:
     @semantic_child_count.setter
     def semantic_child_count(self, value: Optional[int]):
         self._set_attr("semanticChildCount", value)
+
+    # build_controls_on_demand
+    @property
+    def build_controls_on_demand(self) -> Optional[bool]:
+        return self._get_attr("buildControlsOnDemand", data_type="bool", def_value=True)
+
+    @build_controls_on_demand.setter
+    def build_controls_on_demand(self, value: Optional[bool]):
+        self._set_attr("buildControlsOnDemand", value)