Theme Enhancement

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

@@ -117,8 +117,7 @@ class _TabsControlState extends State<TabsControl>
             overlayColor = getMaterialStateProperty<Color?>(
                     json.decode(overlayColorStr),
                     (jv) =>
-                        HexColor.fromString(Theme.of(context), jv as String),
-                    null) ??
+                        HexColor.fromString(Theme.of(context), jv as String)) ??
                 TabBarTheme.of(context).overlayColor;
           }
 

packages/flet/lib/src/utils/borders.dart

@@ -69,8 +69,8 @@ BorderRadius borderRadiusFromJSON(dynamic json) {
   );
 }
 
-Border borderFromJSON(
-    ThemeData? theme, Map<String, dynamic> json, Color? defaultSideColor) {
+Border borderFromJSON(ThemeData? theme, Map<String, dynamic> json,
+    [Color? defaultSideColor]) {
   return Border(
       top: borderSideFromJSON(theme, json['t'], defaultSideColor) ??
           BorderSide.none,
@@ -82,8 +82,8 @@ Border borderFromJSON(
           BorderSide.none);
 }
 
-BorderSide? borderSideFromJSON(
-    ThemeData? theme, dynamic json, Color? defaultSideColor) {
+BorderSide? borderSideFromJSON(ThemeData? theme, dynamic json,
+    [Color? defaultSideColor]) {
   return json != null
       ? BorderSide(
           color: json['c'] != null

packages/flet/lib/src/utils/buttons.dart

@@ -40,18 +40,16 @@ ButtonStyle? parseButtonStyle(ThemeData theme, Control control, String propName,
       defaultShape);
 }
 
-ButtonStyle? buttonStyleFromJSON(
-    ThemeData theme,
-    Map<String, dynamic> json,
-    Color defaultForegroundColor,
-    Color defaultBackgroundColor,
-    Color defaultOverlayColor,
-    Color defaultShadowColor,
-    Color defaultSurfaceTintColor,
-    double defaultElevation,
-    EdgeInsets defaultPadding,
-    BorderSide defaultBorderSide,
-    OutlinedBorder defaultShape) {
+ButtonStyle? buttonStyleFromJSON(ThemeData theme, Map<String, dynamic> json,
+    [Color? defaultForegroundColor,
+    Color? defaultBackgroundColor,
+    Color? defaultOverlayColor,
+    Color? defaultShadowColor,
+    Color? defaultSurfaceTintColor,
+    double? defaultElevation,
+    EdgeInsets? defaultPadding,
+    BorderSide? defaultBorderSide,
+    OutlinedBorder? defaultShape]) {
   return ButtonStyle(
       foregroundColor: getMaterialStateProperty<Color?>(
           json["color"],

packages/flet/lib/src/utils/colors.dart

@@ -137,7 +137,7 @@ Map<String, MaterialAccentColor> _materialAccentColors = {
 
 // https://stackoverflow.com/questions/50081213/how-do-i-use-hexadecimal-color-strings-in-flutter
 extension HexColor on Color {
-  static Color? fromString(ThemeData? theme, String colorString) {
+  static Color? fromString(ThemeData? theme, [String colorString = ""]) {
     var colorParts = colorString.split(",");
 
     var colorValue = colorParts[0];
@@ -245,5 +245,5 @@ MaterialStateProperty<Color?>? parseMaterialStateColor(
 
   final j1 = json.decode(v);
   return getMaterialStateProperty<Color?>(
-      j1, (jv) => HexColor.fromString(theme, jv as String), null);
+      j1, (jv) => HexColor.fromString(theme, jv as String));
 }

packages/flet/lib/src/utils/icons.dart

@@ -21,5 +21,5 @@ MaterialStateProperty<Icon?>? parseMaterialStateIcon(
   final j1 = json.decode(v);
 
   return getMaterialStateProperty<Icon?>(
-      j1, (jv) => Icon(parseIcon(jv as String)), null);
+      j1, (jv) => Icon(parseIcon(jv as String)));
 }

packages/flet/lib/src/utils/material_state.dart

@@ -1,7 +1,7 @@
 import 'package:flutter/material.dart';
 
-MaterialStateProperty<T?>? getMaterialStateProperty<T>(dynamic jsonDictValue,
-    T Function(dynamic) converterFromJson, T defaultValue) {
+MaterialStateProperty<T?>? getMaterialStateProperty<T>(dynamic jsonDictValue, T Function(dynamic) converterFromJson,
+    [T? defaultValue]) {
   if (jsonDictValue == null) {
     return null;
   }
@@ -14,9 +14,9 @@ MaterialStateProperty<T?>? getMaterialStateProperty<T>(dynamic jsonDictValue,
 
 class MaterialStateFromJSON<T> extends MaterialStateProperty<T?> {
   late final Map<String, T> _states;
-  late final T _defaultValue;
+  late final T? _defaultValue;
   MaterialStateFromJSON(Map<String, dynamic>? jsonDictValue,
-      T Function(dynamic) converterFromJson, T defaultValue) {
+      T Function(dynamic) converterFromJson, T? defaultValue) {
     _defaultValue = defaultValue;
     _states = {};
     if (jsonDictValue != null) {

packages/flet/lib/src/utils/menu.dart

@@ -41,18 +41,16 @@ MenuStyle? parseMenuStyle(ThemeData theme, Control control, String propName,
       defaultShape);
 }
 
-MenuStyle? menuStyleFromJSON(
-    ThemeData theme,
-    Map<String, dynamic> json,
-    Color? defaultBackgroundColor,
+MenuStyle? menuStyleFromJSON(ThemeData theme, Map<String, dynamic> json,
+    [Color? defaultBackgroundColor,
     Color? defaultShadowColor,
     Color? defaultSurfaceTintColor,
     double? defaultElevation,
     Alignment? defaultAlignment,
     MouseCursor? defaultMouseCursor,
     EdgeInsets? defaultPadding,
     BorderSide? defaultBorderSide,
-    OutlinedBorder? defaultShape) {
+    OutlinedBorder? defaultShape]) {
   return MenuStyle(
     alignment: json["alignment"] != null
         ? alignmentFromJson(json["alignment"])