bottom_nav_layout 1.0.0

A quick and powerful app layout. Supports page state preservation, lazy page loading, and has a page backstack.

What is bottom_nav_layout?

It is a quick flutter app layout for building an app with a bottom nav bar. You can get an app with fluent behavior running in 15 lines of code.

Why bottom_nav_layout?

• Eliminates all boilerplate code for bottom nav bar coordination.
• Supports multiple, beautiful bar designs.
• Uses identical APIs with the underlying bottom bars.
• Offers additional common features, all of which are optional.
  • Page state preservation
  • Lazy page loading
  • Page backstack
  • Back button navigation management
  • Bar Styling

Content

• Usage
• Page State Preservation
• Lazy Page Loading
• Page Back Stack
• In-Page Navigation Using GlobalKeys
• Different Bar Designs
• Bar Styling
• Improvements
• Community

Usage

Installation

Add the following to your pubspec.yaml file.

dependencies:
  bottom_nav_layout: latest_version

Import

import 'package:bottom_nav_layout/bottom_nav_layout.dart';

Quick Start Example

void main() => runApp(MaterialApp(
      home: BottomNavLayout(
        // The app's top level destinations
        pages: [
          Center(child: Text("Welcome to bottom_nav_layout")),
          SliderPage(),
          Center(child: TextField(decoration: InputDecoration(hintText: 'Go...'))),
        ],
        items: [
          BottomNavigationBarItem(icon: Icon(Icons.home), label: 'Home'),
          BottomNavigationBarItem(icon: Icon(Icons.linear_scale), label: 'Slider'),
          BottomNavigationBarItem(icon: Icon(Icons.search), label: 'Search'),
        ],
      ),
    ));

Done. You have a complete, working application.

SliderPage code

class SliderPage extends StatefulWidget {
  @override
  _SliderPageState createState() => _SliderPageState();
}

class _SliderPageState extends State<SliderPage> {
  double r = 0;

  @override
  Widget build(BuildContext context) => Center(
        child: Slider(
          value: r,
          onChanged: (double d) => setState(() => r = d),
        ),
      );
}

Parameters

• pages - Top level destinations of your application.
• pageBuilders - Also top level destinations but can be lazily loaded.
• savePageState - Flag to enable/disable saving page state.
• pageStack - Navigation stack that remembers pages visited.
• keys - Keys that help the layout manage in-page navigation.
• bottomBarStyler - Widget that wrap bottom bar.
• extendBody - Extends the page behind the bottom bar.
• Rest of the parameters such as items, selectedItemColor, elevation etc. are used to construct the bottom bar. The layout uses flutter's BottomNavigationBar under the hood. The API is identical (except currentIndex, which is same as pageStack.peek()).

Page State Preservation

The state changes you made in a page such as scroll amount, sub-navigation, form inputs etc. are preserved. You can enable it as per Cupertino Design Guidelines or disable it as per Material Design Guidelines

BottomNavLayout(
  // ...
  savePageState: true, // Default is true
)

Lazy Page Loading

Instead of passing pages, pass pageBuilders.

pageBuilders are simple Functions that immediately return the corresponding page. When used, the pages are not created until they are navigated to for the first time. This is useful when a non-initial page has a load animation or runs an unnecessary heavy process.

BottomNavLayout(
  // ...
  pageBuilders: [
    () => Center(child: Text("Welcome to bottom_nav_layout")),
    () => GamePage('TicTacToe'),
    () => Center(child: TextField(decoration: InputDecoration(hintText: 'Search...'))),
  ],
)

Page Back Stack

The layout remembers the order of pages navigated and when back button is pressed, navigates back to the previously navigated page. There are different ways of organizing a page back stack, many of which are readily implemented. You can also implement your own.

Page Back Stack Types

Consider the following use case. After launching the app, the user;

• Start at page 0
• Navigate to page 1
• Navigate to page 2
• Navigate to page 1
• Press back button
• Navigate to page 0
• Press back button

Let's look at how different PageStacks behave in this scenario.

StandardPageStack

This behavior is used by Google Play app.

Event	Initial	push(1)	push(2)	push(1)	pop()	push(0)	pop()
Stack	0	0->1	0->1->2	0->1->2->1	0->1->2	0->1->2->0	0->1->2

ReorderToFrontPageStack

This is the default behavior. This behavior is used by Instagram, Reddit, and Netflix apps.

Event	Initial	push(1)	push(2)	push(1)	pop()	push(0)	pop()
Stack	0	0->1	0->1->2	0->2->1	0->2	2->0	2

ReorderToFrontExceptFirstPageStack

This behavior is used by Youtube app.

Event	Initial	push(1)	push(2)	push(1)	pop()	push(0)	pop()
Stack	0	0->1	0->1->2	0->2->1	0->2	0->2->0	0->2

ReplacePageStack

This behavior is the same as the behavior in BottomNavigationBar example given in flutter docs. It is used by a lot of applications. It is also both Cupertino's and Material's default behavior.

Event	Initial	push(1)	push(2)	push(1)	pop()	push(0)	pop()
Stack	0	1	2	1	Exit App	N/A	N/A

ReplaceExceptFirstPageStack

This behavior is used by Google, Gmail, Facebook, and Twitter apps.

Event	Initial	push(1)	push(2)	push(1)	pop()	push(0)	pop()
Stack	0	0->1	0->2	0->1	0	0	Exit App

Using Page Stacks

BottomNavLayout(
  // ...
  pageStack: StandardPageStack(initialPage: 0),
  // pageStack: ReorderToFrontPageStack(initialPage: 0),
  // pageStack: ReplacePageStack(initialPage: 0),
  // pageStack: ReplaceExceptFirstPageStack(initialPage: 0),
  // pageStack: ReorderToFrontExceptFirstPageStack(initialPage: 0),
)

In-Page Navigation Using GlobalKeys

To be filled...

To use keys, pass all the keys you passed to the pages in the same order.

BottomNavLayout(
  // ...
  keys: <GlobalKey<NavigatorState>?>[
    homePageKey,
    null, // If a page doesn't use a key, pass null so that layout knows the order.
    placePageKey,
  ],
)

Different Bar Designs

So far, we only worked on Material design bottom nav bar. The layout also supports other bar designs.

Salomon Bottom Bar

It is possible to use salomon_bottom_bar with the layout.

Add the following to your pubspac.yaml file.

salomon_bottom_bar: latest_version

And use the following quick start example.

void main() => runApp(MaterialApp(
      home: SalomonBottomNavLayout(
        // The app's top level destinations
        pages: [
          Center(child: Text("Welcome to bottom_nav_layout")),
          GamePage('TicTacToe'),
          Center(child: TextField(decoration: InputDecoration(hintText: 'Search...'))),
        ],
        items: [
          SalomonBottomBarItem(icon: Icon(Icons.home), title: Text('Home')),
          SalomonBottomBarItem(icon: Icon(Icons.gamepad), title: Text('Game')),
          SalomonBottomBarItem(icon: Icon(Icons.search), title: Text('Search')),
        ],
      ),
    ));

Bar Styling

Bar Styler

Do you not like how your bottom bar looks? You can style it by wrapping it inside any widget.

BottomNavLayout(
  // ...
  bottomBarStyler: (bottomBar) => Padding(
    padding: EdgeInsets.fromLTRB(16, 0, 16, 0),
    child: bottomBar,
  ),
)

Extend Body

You can have the page extend behind the bottom bar.

BottomNavLayout(
  // ...
  extendBody: true,
)

Improvements

• I am planning to add more bottom bar designs, preferably from pub.dev.
• Tell me if you want to see a feature your app has/needs in this package. I will do my best to integrate that.

Community

Any feedback is appreciated. 🚀🚀

If you have queries, feel free to create an issue.

If you would like to contribute, feel free to create a PR.