tweaks (#1806)

* opt: nonnull case

* fix: ImageGrid

* opt: distanceSquared

lib/common/widgets/image/custom_grid_view.dart

@@ -251,7 +251,6 @@ class CustomGridView extends StatelessWidget {
         height: imageHeight * row + space * (row - 1),
         child: ImageGrid(
           space: space,
-          itemCount: length,
           column: column,
           width: imageWidth,
           height: imageHeight,
@@ -318,14 +317,12 @@ class ImageGrid extends MultiChildRenderObjectWidget {
     super.key,
     super.children,
     required this.space,
-    required this.itemCount,
     required this.column,
     required this.width,
     required this.height,
   });
 
   final double space;
-  final int itemCount;
   final int column;
   final double width;
   final double height;
@@ -334,7 +331,6 @@ class ImageGrid extends MultiChildRenderObjectWidget {
   RenderObject createRenderObject(BuildContext context) {
     return RenderImageGrid(
       space: space,
-      itemCount: itemCount,
       column: column,
       width: width,
       height: height,
@@ -345,7 +341,6 @@ class ImageGrid extends MultiChildRenderObjectWidget {
   void updateRenderObject(BuildContext context, RenderImageGrid renderObject) {
     renderObject
       ..space = space
-      ..itemCount = itemCount
       ..column = column
       ..width = width
       ..height = height;
@@ -358,12 +353,10 @@ class RenderImageGrid extends RenderBox
         RenderBoxContainerDefaultsMixin<RenderBox, MultiChildLayoutParentData> {
   RenderImageGrid({
     required double space,
-    required int itemCount,
     required int column,
     required double width,
     required double height,
   }) : _space = space,
-       _itemCount = itemCount,
        _column = column,
        _width = width,
        _height = height;
@@ -373,23 +366,15 @@ class RenderImageGrid extends RenderBox
   set space(double value) {
     if (_space == value) return;
     _space = value;
-    markNeedsPaint();
-  }
-
-  int _itemCount;
-  int get itemCount => _itemCount;
-  set itemCount(int value) {
-    if (_itemCount == value) return;
-    _itemCount = value;
-    markNeedsPaint();
+    markNeedsLayout();
   }
 
   int _column;
   int get column => _column;
   set column(int value) {
-    if (_space == value) return;
+    if (_column == value) return;
     _column = value;
-    markNeedsPaint();
+    markNeedsLayout();
   }
 
   double _width;
@@ -397,7 +382,7 @@ class RenderImageGrid extends RenderBox
   set width(double value) {
     if (_width == value) return;
     _width = value;
-    markNeedsPaint();
+    markNeedsLayout();
   }
 
   double _height;
@@ -405,7 +390,7 @@ class RenderImageGrid extends RenderBox
   set height(double value) {
     if (_height == value) return;
     _height = value;
-    markNeedsPaint();
+    markNeedsLayout();
   }
 
   @override