Add max selected chips param to limit maximum selection.

Ref -> #36

README.md

@@ -211,6 +211,8 @@ Empty screen |  FilterListDialog        |  Selected chip           |  Result fro
 | hideHeader|`bool`|Hide complete header section from filter dialog.|
 | headerCloseIcon|`Widget`|Widget to close the dialog.|
 | hideSelectedTextCount|`bool`|Hide selected text count.|
+| enableOnlySingleSelection|`bool`| Enable only single selection |
+| maximumSelectionLength|`int`| Set maximum selection length.|
 | hideSearchField|`bool`|Hide search text field.|
 | headlineText|`String`|Set header text of filter dialog.|
 | backgroundColor|`Color`|Set background color of filter color|

lib/src/filter_list_delegate.dart

@@ -26,6 +26,28 @@ typedef AppbarBottom = PreferredSizeWidget Function(BuildContext context);
 ///
 /// The [onApplyButtonClick] is a callback which return list of all selected items on apply button click.  if no item is selected then it will return empty list.
 ///
+/// The [applyButtonStyle] is used to configure the apply button's visuals.
+///
+/// The [applyButtonText] is used to configure the apply button's text.
+///
+/// The [buildAppbarBottom] is used to configure the bottom of the appbar.
+///
+/// The [enableOnlySingleSelection] is used to configure the selection mode. If true, only one item can be selected at a time.
+///
+/// The [hideClearSearchIcon] is used to configure the clear search icon. If true, the clear search icon will be hidden.
+///
+/// The [emptySearchChild] is used to configure the empty search child. If null, the empty search child will be a SizedBox.
+///
+/// The [searchFieldHint] is used to configure the search field hint text.
+///
+/// The [theme] is used to configure the theme of the filter list delegate.
+///
+/// The [maximumSelectionLength] is used to configure the maximum number of items that can be selected.
+///
+/// The [selectedListData] is used to configure the list of items that are selected by default.
+///
+/// The [searchFieldStyle] is used to configure the search field's text style.
+///
 /// ### This example shows how to use [FilterListDialog]
 ///
 ///  ``` dart
@@ -74,6 +96,7 @@ class FilterListDelegate<T> extends SearchDelegate<T?> {
 
   final ButtonStyle? applyButtonStyle;
   final List<T>? selectedListData;
+  final int? maximumSelectionLength;
 
   final FilterListDelegateThemeData? theme;
   FilterListDelegate({
@@ -91,6 +114,7 @@ class FilterListDelegate<T> extends SearchDelegate<T?> {
     this.emptySearchChild,
     this.theme,
     this.applyButtonStyle,
+    this.maximumSelectionLength,
     this.hideClearSearchIcon = false,
     this.applyButtonText = 'Apply',
   })  : assert(searchFieldStyle == null || searchFieldDecorationTheme == null,
@@ -151,6 +175,8 @@ One of the tileLabel or suggestionBuilder is required
     TextStyle? searchFieldStyle,
     AppbarBottom? buildAppbarBottom,
     bool enableOnlySingleSelection = false,
+    int? maximumSelectionLength,
+    bool hideClearSearchIcon = false,
     Widget? emptySearchChild,
     FilterListDelegateThemeData? theme,
     ButtonStyle? applyButtonStyle,
@@ -174,6 +200,8 @@ One of the tileLabel or suggestionBuilder is required
         theme: theme,
         applyButtonStyle: applyButtonStyle,
         applyButtonText: applyButtonText!,
+        hideClearSearchIcon: hideClearSearchIcon,
+        maximumSelectionLength: maximumSelectionLength,
       ),
     );
 
@@ -234,9 +262,9 @@ One of the tileLabel or suggestionBuilder is required
   Widget _result(BuildContext ctx) {
     return StateProvider<FilterState<T>>(
       value: FilterState<T>(
-        allItems: listData,
-        selectedItems: selectedListData,
-      ),
+          allItems: listData,
+          selectedItems: selectedListData,
+          maximumSelectionLength: maximumSelectionLength),
       child: FilterListDelegateTheme(
         theme: theme ?? FilterListDelegateThemeData(),
         child: Builder(
@@ -247,6 +275,13 @@ One of the tileLabel or suggestionBuilder is required
               itemBuilder: (context, index) {
                 final theme = FilterListDelegateTheme.of(innerContext);
                 final item = tempList[index];
+                final selected = isSelected(item);
+                // ignore: avoid_bool_literals_in_conditional_expressions
+                final maxSelectionReached = !selected &&
+                        maximumSelectionLength != null &&
+                        selectedItems != null
+                    ? selectedItems!.length >= maximumSelectionLength!
+                    : false;
                 if (suggestionBuilder != null) {
                   return GestureDetector(
                     onTap: () => onItemSelect(context, item),
@@ -268,16 +303,18 @@ One of the tileLabel or suggestionBuilder is required
                             data: theme.listTileTheme,
                             child: ListTile(
                               onTap: () => onItemSelect(context, item),
-                              selected: isSelected(item),
+                              selected: selected,
                               title: _title(context, item, theme.tileTextStyle),
                             ),
                           )
                         : ListTileTheme(
                             data: theme.listTileTheme,
                             child: CheckboxListTile(
-                              value: isSelected(item),
-                              selected: isSelected(item),
-                              onChanged: (value) => onItemSelect(context, item),
+                              value: selected,
+                              selected: selected,
+                              onChanged: maxSelectionReached
+                                  ? null
+                                  : (value) => onItemSelect(context, item),
                               title: _title(context, item, theme.tileTextStyle),
                             ),
                           ),
@@ -308,6 +345,11 @@ One of the tileLabel or suggestionBuilder is required
       if (selectedItems!.contains(item)) {
         selectedItems!.remove(item);
       } else {
+        // Add maximum selection length check
+        if (maximumSelectionLength != null &&
+            selectedItems!.length >= maximumSelectionLength!) {
+          return;
+        }
         selectedItems!.add(item);
       }
       final qq = query;

lib/src/filter_list_dialog.dart

@@ -29,7 +29,6 @@ part 'filter_list_widget.dart';
 ///
 ///
 /// The [onApplyButtonClick] is a callback which return list of all selected items on apply button click.  if no item is selected then it will return empty list.
-/// {@endtemplate}
 /// The [useSafeArea] argument is used to indicate if the dialog should only display in 'safe' areas of the screen not used by the operating system (see [SafeArea] for more details). It is true by default, which means the dialog will not overlap operating system areas. If it is set to false the dialog will only be constrained by the screen size. It can not be null.
 ///
 /// The [useRootNavigator] argument is used to determine whether to push the dialog to the [Navigator] furthest from or nearest to the given context. By default, useRootNavigator is true and the dialog route created by this method is pushed to the root navigator. It can not be null.
@@ -41,6 +40,13 @@ part 'filter_list_widget.dart';
 ///
 /// Defaults to EdgeInsets.symmetric(horizontal: 40.0, vertical: 24.0).
 ///
+/// The [controlButtons] is a list of [ControlButtonType] which is used to display control buttons on dialog.
+///
+/// The [enableOnlySingleSelection] is a boolean which is used to enable/disable single selection mode.
+///
+/// The [maximumSelectionLength] is a integer which is used to limit the maximum selection length.
+/// {@endtemplate}
+///
 /// ### This example shows how to use [FilterListDialog]
 ///
 ///  ``` dart
@@ -76,7 +82,6 @@ part 'filter_list_widget.dart';
 class FilterListDialog {
   static Future display<T extends Object>(
     BuildContext context, {
-
     /// Filter theme
     FilterListThemeData? themeData,
 
@@ -153,6 +158,12 @@ class FilterListDialog {
     /// Default value is [false]
     bool enableOnlySingleSelection = false,
 
+    /// if `maximumSelectionLength` is not null then it will limit the maximum selection length.
+    /// `maximumSelectionLength` should be greater than 0. If `maximumSelectionLength` is less than 0 then it will throw an exception.
+    /// Only works when `enableOnlySingleSelection` is false.
+    /// Default value is [null]
+    int? maximumSelectionLength,
+
     /// Background color of dialog box.
     Color backgroundColor = Colors.white,
 
@@ -225,6 +236,7 @@ class FilterListDialog {
                 resetButtonText: resetButtonText,
                 allButtonText: allButtonText,
                 validateRemoveItem: validateRemoveItem,
+                maximumSelectionLength: maximumSelectionLength,
                 controlButtons: controlButtons ??
                     [ControlButtonType.All, ControlButtonType.Reset],
               ),

lib/src/filter_list_widget.dart

@@ -72,6 +72,7 @@ class FilterListWidget<T extends Object> extends StatelessWidget {
     this.hideHeader = false,
     this.backgroundColor = Colors.white,
     this.enableOnlySingleSelection = false,
+    this.maximumSelectionLength,
     this.allButtonText = 'All',
     this.applyButtonText = 'Apply',
     this.resetButtonText = 'Reset',
@@ -120,6 +121,12 @@ class FilterListWidget<T extends Object> extends StatelessWidget {
   /// Default value is `false`
   final bool enableOnlySingleSelection;
 
+  /// if `maximumSelectionLength` is not null then it will limit the maximum selection length.
+  /// `maximumSelectionLength` should be greater than 0. If `maximumSelectionLength` is less than 0 then it will throw an exception.
+  /// Only works when `enableOnlySingleSelection` is false.
+  /// Default value is [null]
+  final int? maximumSelectionLength;
+
   /// The `onApplyButtonClick` is a callback which return list of all selected items on apply button click.  if no item is selected then it will return empty list.
   final OnApplyButtonClick<T>? onApplyButtonClick;
 
@@ -206,6 +213,7 @@ class FilterListWidget<T extends Object> extends StatelessWidget {
                   enableOnlySingleSelection: enableOnlySingleSelection,
                   validateSelectedItem: validateSelectedItem,
                   validateRemoveItem: validateRemoveItem,
+                  maximumSelectionLength: maximumSelectionLength,
                 ),
               ),
             ],
@@ -214,6 +222,7 @@ class FilterListWidget<T extends Object> extends StatelessWidget {
           // /// Bottom section for control buttons
           ControlButtonBar<T>(
             controlButtons: controlButtons,
+            maximumSelectionLength: maximumSelectionLength,
             allButtonText: allButtonText,
             applyButtonText: applyButtonText,
             resetButtonText: resetButtonText,

lib/src/state/filter_state.dart

@@ -2,13 +2,17 @@ import 'package:filter_list/src/state/provider.dart';
 import 'package:flutter/material.dart';
 
 class FilterState<K> extends ListenableState {
-  FilterState({List<K>? allItems, List<K>? selectedItems}) {
+  FilterState(
+      {List<K>? allItems,
+      List<K>? selectedItems,
+      this.maximumSelectionLength}) {
     this.selectedItems = selectedItems;
     items = allItems;
   }
 
   static FilterState<T> of<T>(BuildContext context) =>
       StateProvider.of<FilterState<T>>(context);
+  final int? maximumSelectionLength;
 
   /// List of all items
   List<K>? _items;

lib/src/widget/choice_chip_widget.dart

@@ -9,12 +9,14 @@ class ChoiceChipWidget<T> extends StatelessWidget {
     this.selected,
     this.onSelected,
     this.choiceChipBuilder,
+    this.disabled = false,
   }) : super(key: key);
 
   final String? text;
   final bool? selected;
   final void Function(bool)? onSelected;
   final T? item;
+  final bool disabled;
 
   /// Builder for custom choice chip
   final ChoiceChipBuilder? choiceChipBuilder;
@@ -66,7 +68,7 @@ class ChoiceChipWidget<T> extends StatelessWidget {
                 labelStyle: getSelectedTextStyle(context),
                 visualDensity: theme.visualDensity,
                 selected: selected!,
-                onSelected: onSelected,
+                onSelected: disabled ? null : onSelected,
                 elevation: theme.elevation,
                 side: getSide(context),
                 shape: getShape(context),

lib/src/widget/choice_list.dart

@@ -12,12 +12,14 @@ class ChoiceList<T> extends StatelessWidget {
     this.choiceChipLabel,
     this.enableOnlySingleSelection = false,
     this.validateRemoveItem,
+    this.maximumSelectionLength,
   }) : super(key: key);
   final ValidateSelectedItem<T> validateSelectedItem;
   final ChoiceChipBuilder? choiceChipBuilder;
   final LabelDelegate<T>? choiceChipLabel;
   final bool enableOnlySingleSelection;
   final ValidateRemoveItem<T>? validateRemoveItem;
+  final int? maximumSelectionLength;
 
   List<Widget> _buildChoiceList(BuildContext context) {
     final theme = FilterListTheme.of(context).controlBarButtonTheme;
@@ -30,9 +32,15 @@ class ChoiceList<T> extends StatelessWidget {
     final List<Widget> choices = [];
     for (final item in items) {
       final selected = validateSelectedItem(selectedListData, item);
+
+      // Check if maximum selection length reached
+      final maxSelectionReached = maximumSelectionLength != null &&
+          state.selectedItems != null &&
+          state.selectedItems!.length >= maximumSelectionLength!;
       choices.add(
         ChoiceChipWidget(
           choiceChipBuilder: choiceChipBuilder,
+          disabled: maxSelectionReached,
           item: item,
           onSelected: (value) {
             if (enableOnlySingleSelection) {
@@ -48,6 +56,10 @@ class ChoiceList<T> extends StatelessWidget {
                   state.removeSelectedItem(item);
                 }
               } else {
+                // Add maximum selection length check
+                if (maxSelectionReached && !selected) {
+                  return;
+                }
                 state.addSelectedItem(item);
               }
             }

lib/src/widget/control_button_bar.dart

@@ -5,6 +5,10 @@ import 'package:filter_list/src/state/provider.dart';
 import 'package:filter_list/src/widget/control_button.dart';
 import 'package:flutter/material.dart';
 
+/// {@template control_buttons}
+/// control buttons to show on bottom of dialog along with 'Apply' button.
+/// Generally used to show 'All', 'Reset' and 'Apply' button.
+/// {@endtemplate}
 class ControlButtonBar<T> extends StatelessWidget {
   const ControlButtonBar({
     Key? key,
@@ -13,13 +17,15 @@ class ControlButtonBar<T> extends StatelessWidget {
     this.resetButtonText,
     this.applyButtonText,
     this.onApplyButtonClick,
+    this.maximumSelectionLength,
     required this.controlButtons,
   }) : super(key: key);
   final bool enableOnlySingleSelection;
   final String? allButtonText;
   final String? resetButtonText;
   final String? applyButtonText;
   final VoidCallback? onApplyButtonClick;
+  final int? maximumSelectionLength;
 
   /// {@macro control_buttons}
   final List<ControlButtonType> controlButtons;
@@ -48,7 +54,8 @@ class ControlButtonBar<T> extends StatelessWidget {
                   mainAxisSize: MainAxisSize.min,
                   children: <Widget>[
                     /* All Button */
-                    if (!enableOnlySingleSelection &&
+                    if (maximumSelectionLength == null &&
+                        !enableOnlySingleSelection &&
                         controlButtons.contains(ControlButtonType.All)) ...[
                       ControlButton(
                         choiceChipLabel: '$allButtonText',