Feature/navgation body builder (bdlukaa#77)

CHANGELOG.md

@@ -1,5 +1,9 @@
 Date format: DD/MM/YYYY
 
+## [3.x.x] - Flutter 2.5.0 - [DD/MM/YYYY]
+
+- Added builder variant to `NavigationBody`. 
+
 ## [3.2.0] - Flutter 2.5.0 - [15/09/2021]
 
 - Added missing parameters in `_FluentTextSelectionControls` methods ([#67](https://github.com/bdlukaa/fluent_ui/issues/67))

README.md

@@ -493,10 +493,12 @@ pane: NavigationPane(
 
 ### Navigation body
 
-A navigation body is used to implement page transitions into a navigation view. It knows what is the current diplay mode of the parent `NavigationView`, if any, and define the page transitions accordingly.
+A navigation body is used to implement page transitions into a navigation view. It knows what is the current display mode of the parent `NavigationView`, if any, and define the page transitions accordingly.
 
 For top mode, the horizontal page transition is used. For the others, drill in page transition is used.
 
+You can also supply a builder function to create the pages instead of a list of widgets. For this use the `NavigationBody.builder` constructor. 
+
 ```dart
 int _currentIndex = 0;
 
@@ -985,12 +987,12 @@ String? comboBoxValue;
 
 SizedBox(
   width: 200,
-  child: ComboBox<String>(
+  child: Combobox<String>(
     header: 'Colors',
     placeholder: 'Selected list item',
     isExpanded: true,
     items: values
-        .map((e) => ComboboxMenuItem<String>(
+        .map((e) => ComboboxItem<String>(
               value: e,
               child: Text(e),
             ))
@@ -1457,7 +1459,7 @@ The list of equivalents between this library and `flutter/material.dart`
 | -                         | ToggleButton     |
 | Switch                    | ToggleSwitch     |
 | TextField                 | TextBox          |
-| DropdownButton            | ComboBox         |
+| DropdownButton            | Combobox         |
 | -                         | AutoSuggestBox   |
 | AlertDialog               | ContentDialog    |
 | MaterialBanner            | InfoBar          |

lib/src/controls/navigation/navigation_view/body.dart

@@ -1,3 +1,4 @@
+// ignore_for_file: prefer_initializing_formals
 part of 'view.dart';
 
 /// A helper widget that implements fluent page transitions into
@@ -13,18 +14,43 @@ class NavigationBody extends StatefulWidget {
   const NavigationBody({
     Key? key,
     required this.index,
-    required this.children,
+    required List<Widget> children,
     this.transitionBuilder,
     this.animationCurve,
     this.animationDuration,
   })  : assert(index >= 0 && index <= children.length),
+        children = children,
+        itemBuilder = null,
+        itemCount = null,
         super(key: key);
 
-  /// The pages this body can have.
-  final List<Widget> children;
+  /// Creates a navigation body that uses a builder to supply child pages
+  ///
+  /// [index] must be greater than 0 and less than [itemCount] if it is provided
+  const NavigationBody.builder({
+    Key? key,
+    required this.index,
+    required IndexedWidgetBuilder itemBuilder,
+    this.itemCount,
+    this.transitionBuilder,
+    this.animationCurve,
+    this.animationDuration,
+  })  : assert(index >= 0 && (itemCount == null || index <= itemCount)),
+        itemBuilder = itemBuilder,
+        children = null,
+        super(key: key);
+
+  /// The pages this body can have
+  final List<Widget>? children;
+
+  /// The builder that will be used to build the pages
+  final IndexedWidgetBuilder? itemBuilder;
+
+  /// Optional number of items to assume builder can create.
+  final int? itemCount;
 
   /// The current page index. It must be greater than 0 and less
-  /// than [children.length].
+  /// than [children.length] or [itemCount].
   final int index;
 
   /// The transition builder.
@@ -122,7 +148,8 @@ class _NavigationBodyState extends State<NavigationBody> {
         },
         child: SizedBox(
           key: ValueKey<int>(widget.index),
-          child: widget.children[widget.index],
+          child: widget.itemBuilder?.call(context, widget.index) ??
+              widget.children![widget.index],
         ),
       ),
     );