Provide default method call handler for SystemChannels.textInput (#101087)

Author: fbcouch

packages/flutter/lib/src/services/binding.dart

@@ -17,6 +17,7 @@ import 'message_codec.dart';
 import 'raw_keyboard.dart';
 import 'restoration.dart';
 import 'system_channels.dart';
+import 'text_input.dart';
 
 /// Listens for platform messages and directs them to the [defaultBinaryMessenger].
 ///
@@ -36,6 +37,7 @@ mixin ServicesBinding on BindingBase, SchedulerBinding {
     SystemChannels.system.setMessageHandler((dynamic message) => handleSystemMessage(message as Object));
     SystemChannels.lifecycle.setMessageHandler(_handleLifecycleMessage);
     SystemChannels.platform.setMethodCallHandler(_handlePlatformMessage);
+    TextInput.ensureInitialized();
     readInitialLifecycleStateFromNativeWindow();
   }
 

packages/flutter/lib/src/services/text_input.dart

@@ -1575,6 +1575,12 @@ class TextInput {
     TextInputAction.emergencyCall,
   ];
 
+  /// Ensure that a [TextInput] instance has been set up so that the platform
+  /// can handle messages on the text input method channel.
+  static void ensureInitialized() {
+    _instance; // ignore: unnecessary_statements
+  }
+
   /// Begin interacting with the text input control.
   ///
   /// Calling this function helps multiple clients coordinate about which one is

packages/flutter/test/services/binding_test.dart

@@ -107,4 +107,11 @@ void main() {
     await rootBundle.loadString('test_asset2');
     expect(flutterAssetsCallCount, 4);
   });
+
+  test('initInstances sets a default method call handler for SystemChannels.textInput', () async {
+    final ByteData message = const JSONMessageCodec().encodeMessage(<String, dynamic>{'method': 'TextInput.requestElementsInRect', 'args': null})!;
+    await ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage('flutter/textinput', message, (ByteData? data) {
+      expect(data, isNotNull);
+     });
+  });
 }