Added widget reacting on keyboard visibility changes

lib/keyboard_visibility_builder.dart

@@ -0,0 +1,88 @@
+import 'package:flutter/material.dart';
+import 'package:keyboard_visibility/keyboard_visibility.dart';
+
+/// A Widget reacting on keyboard visibility changes using [KeyboardVisibilityNotification]  and triggering a rebuild
+class KeyboardVisibilityBuilder extends StatefulWidget {
+
+  /// Builder used to create child widget
+  final Widget Function(BuildContext, bool) builder;
+
+  /// Callback for when the current visibility state of the keyboard changes
+  final void Function(bool) onChange;
+
+  /// Callback for when the keyboard gets opened
+  final void Function() onShow;
+
+  /// Callback for when the keyboard gets closed
+  final void Function() onHide;
+
+  /// Constructs a new [KeyboardVisibilityBuilder]
+  KeyboardVisibilityBuilder({this.builder, this.onChange, this.onHide, this.onShow});
+
+  @override
+  _KeyboardVisibilityBuilderState createState() => _KeyboardVisibilityBuilderState();
+}
+
+class _KeyboardVisibilityBuilderState extends State<KeyboardVisibilityBuilder> {
+
+  /// Holds the id defined by the notifier for later unsubscribing
+  int _subscribingId;
+
+  /// Holds the notifier which will send the keyboard events 
+  KeyboardVisibilityNotification _notifier;
+
+  /// Holds the current visibility state of the Keyboard
+  bool _keyboardVisible = false;
+
+  @override
+  void initState() { 
+
+    _notifier = KeyboardVisibilityNotification();
+
+    /// Register the listener for updating the [_keyboardVisible] variable and triggering the rebuild
+    _subscribingId = _notifier.addNewListener(
+      onChange: (value) => _onVisibilityChanged(value),
+      onHide: () => _onHide(),
+      onShow: () => _onShow(),
+    );
+    super.initState();
+  }
+
+  @override
+  void dispose() {
+    /// Removes the listener when the widget gets disposed
+    _notifier.removeListener(_subscribingId);
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    /// Building child using the [builder] parsed to the constructor
+    return widget.builder(context, _keyboardVisible);
+  }
+
+  /// Callback which gets called by [_notifier] when the keyboard visibility gets changed
+  void _onVisibilityChanged(bool isVisible) {
+    setState(() {
+      _keyboardVisible = isVisible;
+    });
+
+    if (widget.onChange != null) {
+      widget.onChange(isVisible);
+    } 
+  }
+
+  /// Callback which gets called by [_notifier] when the keyboard gets dismissed
+  void _onHide() {
+    if (widget.onHide != null) {
+      widget.onHide();
+    }
+  }
+
+  /// Callback which gets called by [_notifier] when the keyboard gets opened
+  void _onShow() {
+    if (widget.onShow != null) {
+      widget.onShow();
+    }
+  }
+}