flutter-plugins/example/lib/extensions/keys_ext.dart

import 'package:flutter/material.dart';

/// Extensions for [GlobalKey]
extension ExtGlobalKey on GlobalKey {
  /// Get height by key
  double? getHeight() {
    if (currentContext == null) {
      return null;
    }
    try {
      final renderBoxRed = currentContext!.findRenderObject() as RenderBox;
      final sizeRed = renderBoxRed.size;
      return sizeRed.height;
    } catch (e) {
      return 0;
    }
  }
}