[animated_collection] ✨ Add AnimatedVisibility.builder

packages/animated_collection/CHANGELOG.md

@@ -1,3 +1,7 @@
+## NEXT
+
+- Adds `AnimatedVisibility.builder`.
+
 ## 1.2.1
 
 - Fix memory leaks in `AnimatedLocation`.

packages/animated_collection/example/.gitignore

@@ -5,9 +5,11 @@
 *.swp
 .DS_Store
 .atom/
+.build/
 .buildlog/
 .history
 .svn/
+.swiftpm/
 migrate_working_dir/
 
 # IntelliJ related

packages/animated_collection/example/macos/Runner.xcodeproj/xcshareddata/xcschemes/Runner.xcscheme

@@ -59,6 +59,7 @@
       ignoresPersistentStateOnLaunch = "NO"
       debugDocumentVersioning = "YES"
       debugServiceExtension = "internal"
+      enableGPUValidationMode = "1"
       allowLocationSimulation = "YES">
       <BuildableProductRunnable
          runnableDebuggingMode = "0">

packages/animated_collection/example/macos/Runner/AppDelegate.swift

@@ -1,9 +1,13 @@
 import Cocoa
 import FlutterMacOS
 
-@NSApplicationMain
+@main
 class AppDelegate: FlutterAppDelegate {
   override func applicationShouldTerminateAfterLastWindowClosed(_ sender: NSApplication) -> Bool {
     return true
   }
+
+  override func applicationSupportsSecureRestorableState(_ app: NSApplication) -> Bool {
+    return true
+  }
 }

packages/animated_collection/lib/src/widgets/animated_visibility.dart

@@ -3,23 +3,74 @@ import 'package:flutter/material.dart';
 
 import 'animated_size_transition.dart';
 
-/// Displays the child when [visible] is `true` and a [SizedBox.shrink] when
-/// [visible] is `false`, but does it with a size transition.
+/// Conditionally renders the child with an animated size transition when
+/// [visible] is `true`; otherwise renders a [SizedBox.shrink].
 class AnimatedVisibility extends StatelessWidget {
-  /// Displays the child when [visible] is `true` and a [SizedBox.shrink] when
-  /// [visible] is `false`, but does it with a size transition.
+  /// Conditionally renders the child with an animated size transition when
+  /// [visible] is `true`; otherwise renders a [SizedBox.shrink].
   const AnimatedVisibility({
     required this.visible,
-    required this.child,
+    this.child,
     this.axis = Axis.vertical,
     this.axisAlignment = 0,
     this.curve = Curves.easeInOut,
     this.duration = defaultDuration,
     super.key,
-  });
+  }) : builder = null;
+
+  /// Shows the widget returned by [builder] when [visible] is `true`, and a
+  /// [SizedBox.shrink] when [visible] is `false`, with a smooth size
+  /// transition.
+  ///
+  /// This constructor is helpful when the widget relies on data that’s only
+  /// available when [visible] is `true`.
+  ///
+  /// For instance, the following example would throw an error:
+  ///
+  /// ```dart
+  /// String? text;
+  /// AnimatedVisibility(
+  ///   visible: text != null,
+  ///   child: Text(text!), // Throws if text is null
+  /// )
+  /// ```
+  ///
+  /// To prevent that, you’d need to handle the null case explicitly:
+  ///
+  /// ```dart
+  /// String? text;
+  /// AnimatedVisibility(
+  ///   visible: text != null,
+  ///   child: Text(text ?? ''),
+  /// )
+  /// ```
+  ///
+  /// With [AnimatedVisibility.builder], you can safely access the non-null data
+  /// inside the builder without extra null checks:
+  ///
+  /// ```dart
+  /// String? text;
+  /// AnimatedVisibility.builder(
+  ///   visible: text != null,
+  ///   builder: (context) => Text(text!),
+  /// )
+  /// ```
+
+  const AnimatedVisibility.builder({
+    required this.visible,
+    this.builder,
+    this.axis = Axis.vertical,
+    this.axisAlignment = 0,
+    this.curve = Curves.easeInOut,
+    this.duration = defaultDuration,
+    super.key,
+  }) : child = null;
 
   /// {@macro flutter.widgets.ProxyWidget.child}
-  final Widget child;
+  final Widget? child;
+
+  /// Called to obtain the child widget.
+  final WidgetBuilder? builder;
 
   /// If `true`, it displays the [child], else if displays a [SizedBox.shrink].
   final bool visible;
@@ -44,7 +95,7 @@ class AnimatedVisibility extends StatelessWidget {
       curve: curve,
       fixedCrossAxisSizeFactor: 1,
       duration: duration,
-      child: visible ? child : const SizedBox.shrink(),
+      child: visible ? child ?? builder!(context) : const SizedBox.shrink(),
     );
   }
 }