Add handling of 'TextInput.clearClient' message from platform to framework (#35054). (#35100)

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

@@ -632,7 +632,7 @@ abstract class TextInputClient {
 /// See also:
 ///
 ///  * [TextInput.attach]
-class TextInputConnection {
+class TextInputConnection with ChangeNotifier {
   TextInputConnection._(this._client)
     : assert(_client != null),
       _id = _nextId++;
@@ -667,12 +667,19 @@ class TextInputConnection {
   void close() {
     if (attached) {
       SystemChannels.textInput.invokeMethod<void>('TextInput.clearClient');
-      _clientHandler
-        .._currentConnection = null
-        .._scheduleHide();
+      _onConnectionClosed();
+      _clientHandler._scheduleHide();
     }
     assert(!attached);
   }
+
+  /// Clear out the current text input connection.
+  ///
+  /// Call this method when the current text input connection has cleared.
+  void _onConnectionClosed() {
+    _clientHandler._currentConnection = null;
+    notifyListeners();
+  }
 }
 
 TextInputAction _toTextInputAction(String action) {
@@ -753,6 +760,9 @@ class _TextInputClientHandler {
       case 'TextInputClient.updateFloatingCursor':
         _currentConnection._client.updateFloatingCursor(_toTextPoint(_toTextCursorAction(args[1]), args[2]));
         break;
+      case 'TextInputClient.onConnectionClosed':
+        _currentConnection._onConnectionClosed();
+        break;
       default:
         throw MissingPluginException();
     }

packages/flutter/test/services/text_input_test.dart

@@ -85,5 +85,44 @@ void main() {
       expect(signed.hashCode == signedDecimal.hashCode, false);
       expect(decimal.hashCode == signedDecimal.hashCode, false);
     });
+
+    test('The framework TextInputConnection closes when the platform loses its input connection', () async {
+      // Assemble a TextInputConnection so we can verify its change in state.
+      final TextInputClient client = NoOpTextInputClient();
+      const TextInputConfiguration configuration = TextInputConfiguration();
+      final TextInputConnection textInputConnection = TextInput.attach(client, configuration);
+
+      // Verify that TextInputConnection think its attached to a client. This is
+      // an intermediate verification of expected state.
+      expect(textInputConnection.attached, true);
+
+      // Pretend that the platform has lost its input connection.
+      final ByteData messageBytes = const JSONMessageCodec().encodeMessage(
+          <String, dynamic>{
+            'args': <dynamic>[1],
+            'method': 'TextInputClient.onConnectionClosed',
+          }
+      );
+      defaultBinaryMessenger.handlePlatformMessage(
+        'flutter/textinput',
+        messageBytes,
+        (ByteData _) {},
+      );
+
+      // Verify that textInputConnection no longer think its attached to an input
+      // connection. This is the critical verification of this test.
+      expect(textInputConnection.attached, false);
+    });
   });
 }
+
+class NoOpTextInputClient extends TextInputClient {
+  @override
+  void performAction(TextInputAction action) {}
+
+  @override
+  void updateEditingValue(TextEditingValue value) {}
+
+  @override
+  void updateFloatingCursor(RawFloatingCursorPoint point) {}
+}
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