feat(ios): Improved AudioContextConfig assertions, fix example (#1619)

# Description

- Improve assertion error messages for `AudioContextConfig` for values
set on iOS
- Fix example, as it could and should not alternate the `options` array
for AudioContextIOS
- Improve example to show assertion errors as toast to the user

packages/audioplayers/example/lib/tabs/audio_context.dart

@@ -3,6 +3,7 @@ import 'package:audioplayers_example/components/cbx.dart';
 import 'package:audioplayers_example/components/drop_down.dart';
 import 'package:audioplayers_example/components/tab_content.dart';
 import 'package:audioplayers_example/components/tabs.dart';
+import 'package:audioplayers_example/utils.dart';
 import 'package:flutter/material.dart';
 
 class AudioContextTab extends StatefulWidget {
@@ -82,10 +83,15 @@ class AudioContextTabState extends State<AudioContextTab>
   }
 
   void updateConfig(AudioContextConfig newConfig) {
-    setState(() {
-      audioContextConfig = newConfig;
-      audioContext = audioContextConfig.build();
-    });
+    try {
+      final context = newConfig.build();
+      setState(() {
+        audioContextConfig = newConfig;
+        audioContext = context;
+      });
+    } on AssertionError catch (e) {
+      toast(e.message.toString());
+    }
   }
 
   void updateAudioContextAndroid(AudioContextAndroid contextAndroid) {
@@ -94,10 +100,15 @@ class AudioContextTabState extends State<AudioContextTab>
     });
   }
 
-  void updateAudioContextIOS(AudioContextIOS contextIOS) {
-    setState(() {
-      audioContext = audioContext.copy(iOS: contextIOS);
-    });
+  void updateAudioContextIOS(AudioContextIOS Function() buildContextIOS) {
+    try {
+      final context = buildContextIOS();
+      setState(() {
+        audioContext = audioContext.copy(iOS: context);
+      });
+    } on AssertionError catch (e) {
+      toast(e.message.toString());
+    }
   }
 
   Widget _genericTab() {
@@ -194,19 +205,20 @@ class AudioContextTabState extends State<AudioContextTab>
   Widget _iosTab() {
     final iosOptions = AVAudioSessionOptions.values.map(
       (option) {
-        final options = audioContext.iOS.options;
+        final options = {...audioContext.iOS.options};
         return Cbx(
           option.name,
           value: options.contains(option),
           ({value}) {
-            if (value ?? false) {
-              options.add(option);
-            } else {
-              options.remove(option);
-            }
-            updateAudioContextIOS(
-              audioContext.iOS.copy(options: options),
-            );
+            updateAudioContextIOS(() {
+              final iosContext = audioContext.iOS.copy(options: options);
+              if (value ?? false) {
+                options.add(option);
+              } else {
+                options.remove(option);
+              }
+              return iosContext;
+            });
           },
         );
       },
@@ -219,7 +231,7 @@ class AudioContextTabState extends State<AudioContextTab>
           options: {for (final e in AVAudioSessionCategory.values) e: e.name},
           selected: audioContext.iOS.category,
           onChange: (v) => updateAudioContextIOS(
-            audioContext.iOS.copy(category: v),
+            () => audioContext.iOS.copy(category: v),
           ),
         ),
         ...iosOptions,

packages/audioplayers/example/lib/utils.dart

@@ -7,7 +7,7 @@ extension StateExt<T extends StatefulWidget> on State<T> {
     ScaffoldMessenger.of(context).showSnackBar(
       SnackBar(
         content: Text(message, key: textKey),
-        duration: const Duration(milliseconds: 250),
+        duration: Duration(milliseconds: message.length * 25),
       ),
     );
   }

packages/audioplayers_platform_interface/lib/src/api/audio_context_config.dart

@@ -107,10 +107,11 @@ class AudioContextConfig {
     );
   }
 
-  AudioContextIOS buildIOS() {
-    if (defaultTargetPlatform == TargetPlatform.iOS) {
-      validateIOS();
+  AudioContextIOS? buildIOS() {
+    if (defaultTargetPlatform != TargetPlatform.iOS) {
+      return null;
     }
+    validateIOS();
     return AudioContextIOS(
       category: respectSilence
           ? AVAudioSessionCategory.ambient
@@ -128,12 +129,28 @@ class AudioContextConfig {
   }
 
   void validateIOS() {
-    // Please create a custom [AudioContextIOS] if the generic flags cannot
-    // represent your needs.
-    if (respectSilence && route == AudioContextConfigRoute.speaker) {
-      throw 'On iOS it is impossible to set both `respectSilence` and route '
-          '`speaker`';
-    }
+    const invalidMsg =
+        'Invalid AudioContextConfig: On iOS it is not possible to set';
+    const tip = 'Please create a custom [AudioContextIOS] if the generic flags '
+        'cannot represent your needs.';
+    assert(
+      !(duckAudio && respectSilence),
+      '$invalidMsg `respectSilence` and `duckAudio`. $tip',
+    );
+    assert(
+      !(respectSilence && route == AudioContextConfigRoute.speaker),
+      '$invalidMsg `respectSilence` and route `speaker`. $tip',
+    );
+  }
+
+  @override
+  String toString() {
+    return 'AudioContextConfig('
+        'route: $route, '
+        'duckAudio: $duckAudio, '
+        'respectSilence: $respectSilence, '
+        'stayAwake: $stayAwake'
+        ')';
   }
 }
 

packages/audioplayers_platform_interface/test/audio_context_test.dart

@@ -1,6 +1,8 @@
 //ignore_for_file: avoid_redundant_argument_values
 
 import 'package:audioplayers_platform_interface/audioplayers_platform_interface.dart';
+import 'package:audioplayers_platform_interface/src/api/audio_context_config.dart';
+import 'package:flutter/foundation.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
@@ -27,6 +29,74 @@ void main() {
     );
   });
 
+  test('Check AudioContextConfig assertions', () async {
+    debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
+    const boolValues = {true, false};
+    const routeValues = AudioContextConfigRoute.values;
+
+    final throwsAssertion = [];
+    for (final isDuckAudio in boolValues) {
+      for (final isRespectSilence in boolValues) {
+        for (final isStayAwake in boolValues) {
+          for (final route in routeValues) {
+            final config = AudioContextConfig(
+              duckAudio: isDuckAudio,
+              respectSilence: isRespectSilence,
+              stayAwake: isStayAwake,
+              route: route,
+            );
+            try {
+              config.build();
+              throwsAssertion.add(false);
+            } on AssertionError catch (e) {
+              if (e.message
+                  .toString()
+                  .startsWith('Invalid AudioContextConfig')) {
+                throwsAssertion.add(true);
+              } else {
+                fail(
+                  'Assertion of $config does not match the expected '
+                  'description. See: $e',
+                );
+              }
+            }
+          }
+        }
+      }
+    }
+
+    // Ensure assertions keep thrown on the correct cases.
+    expect(
+      throwsAssertion,
+      const [
+        true,
+        true,
+        true,
+        true,
+        true,
+        true,
+        false,
+        false,
+        false,
+        false,
+        false,
+        false,
+        false,
+        false,
+        true,
+        false,
+        false,
+        true,
+        false,
+        false,
+        false,
+        false,
+        false,
+        false,
+      ],
+    );
+  });
+
   test('Create invalid AudioContextIOS', () async {
     try {
       // Throws AssertionError: