Envelope/mobile/lib/components/custom_title_bar.dart

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

@immutable
class CustomTitleBar extends StatelessWidget with PreferredSizeWidget {
  const CustomTitleBar({
    Key? key,
    required this.title,
    required this.showBack,
    this.rightHandButton,
    this.backgroundColor,
    this.forgroundColor,
    this.iconColor,
    this.beforeBack,
  }) : super(key: key);

  final Text title;
  final bool showBack;
  final IconButton? rightHandButton;
  final Color? backgroundColor;
  final Color? forgroundColor;
  final Color? iconColor;
  final Future<void> Function()? beforeBack;

  @override
  Size get preferredSize => const Size.fromHeight(kToolbarHeight);

  @override
  Widget build(BuildContext context) {
    return AppBar(
      elevation: 0,
      automaticallyImplyLeading: false,
      backgroundColor:
        backgroundColor != null ?
        backgroundColor! :
        Theme.of(context).appBarTheme.backgroundColor,
      foregroundColor: forgroundColor != null ?
        forgroundColor! :
        Theme.of(context).appBarTheme.foregroundColor,
      flexibleSpace: SafeArea(
        child: Container(
          padding: const EdgeInsets.only(right: 16),
          child: Row(
            children: <Widget>[
              showBack ?
                _backButton(context) :
                const SizedBox.shrink(),
              showBack ?
                const SizedBox(width: 2,) :
                const SizedBox(width: 15),
              Expanded(
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    title,
                  ],
                ),
              ),
              rightHandButton != null ?
                  rightHandButton! :
                  const SizedBox.shrink(),
            ],
          ),
        ),
      ),
    );
  }

  Widget _backButton(BuildContext context) {
    return IconButton(
      onPressed: () {
        if (beforeBack != null) {
          beforeBack!().then((dynamic) => Navigator.pop(context));
          return;
        }
        Navigator.pop(context);
      },
      icon: Icon(
        Icons.arrow_back,
        color: iconColor != null ?
          iconColor! :
          Theme.of(context).appBarTheme.iconTheme?.color,
      ),
    );
  }
}