Change Background When Click on Easy Ui Grids Row

Layouts in Flutter

1. UI
2. Layout

Contents

• Lay out a widget
  • 1. Select a layout widget
  • 2. Create a visible widget
  • 3. Add the visible widget to the layout widget
  • 4. Add the layout widget to the page
    • Material apps
    • Non-Material apps
• Lay out multiple widgets vertically and horizontally
  • Aligning widgets
  • Sizing widgets
  • Packing widgets
  • Nesting rows and columns
• Common layout widgets
  • Standard widgets
  • Material widgets
  • Container
  • GridView
  • ListView
  • Stack
  • Card
  • ListTile
• Constraints
• Videos
• Other resources

The core of Flutter's layout mechanism is widgets. In Flutter, almost everything is a widget—even layout models are widgets. The images, icons, and text that you see in a Flutter app are all widgets. But things you don't see are also widgets, such as the rows, columns, and grids that arrange, constrain, and align the visible widgets.

You create a layout by composing widgets to build more complex widgets. For example, the first screenshot below shows 3 icons with a label under each one:

The second screenshot displays the visual layout, showing a row of 3 columns where each column contains an icon and a label.

Here's a diagram of the widget tree for this UI:

Most of this should look as you might expect, but you might be wondering about the containers (shown in pink). Container is a widget class that allows you to customize its child widget. Use a Container when you want to add padding, margins, borders, or background color, to name some of its capabilities.

In this example, each Text widget is placed in a Container to add margins. The entire Row is also placed in a Container to add padding around the row.

The rest of the UI in this example is controlled by properties. Set an Icon's color using its color property. Use the Text.style property to set the font, its color, weight, and so on. Columns and rows have properties that allow you to specify how their children are aligned vertically or horizontally, and how much space the children should occupy.

How do you lay out a single widget in Flutter? This section shows you how to create and display a simple widget. It also shows the entire code for a simple Hello World app.

In Flutter, it takes only a few steps to put text, an icon, or an image on the screen.

1. Select a layout widget

Choose from a variety of layout widgets based on how you want to align or constrain the visible widget, as these characteristics are typically passed on to the contained widget.

This example uses Center which centers its content horizontally and vertically.

2. Create a visible widget

For example, create a Text widget:

Create an Image widget:

Image.asset(   'images/lake.jpg',   fit: BoxFit.cover, ),

Create an Icon widget:

Icon(   Icons.star,   color: Colors.red[500], ),

3. Add the visible widget to the layout widget

All layout widgets have either of the following:

• A child property if they take a single child—for example, Center or Container
• A children property if they take a list of widgets—for example, Row, Column, ListView, or Stack.

Add the Text widget to the Center widget:

const Center(   child: Text('Hello World'), ),

4. Add the layout widget to the page

A Flutter app is itself a widget, and most widgets have a build() method. Instantiating and returning a widget in the app's build() method displays the widget.

Material apps

For a Material app, you can use a Scaffold widget; it provides a default banner, background color, and has API for adding drawers, snack bars, and bottom sheets. Then you can add the Center widget directly to the body property for the home page.

class MyApp extends StatelessWidget {   const MyApp({super.key});    @override   Widget build(BuildContext context) {     return MaterialApp(       title: 'Flutter layout demo',       home: Scaffold(         appBar: AppBar(           title: const Text('Flutter layout demo'),         ),         body: const Center(           child: Text('Hello World'),         ),       ),     );   } }

Non-Material apps

For a non-Material app, you can add the Center widget to the app's build() method:

class MyApp extends StatelessWidget {   const MyApp({super.key});    @override   Widget build(BuildContext context) {     return Container(       decoration: const BoxDecoration(color: Colors.white),       child: const Center(         child: Text(           'Hello World',           textDirection: TextDirection.ltr,           style: TextStyle(             fontSize: 32,             color: Colors.black87,           ),         ),       ),     );   } }

By default a non-Material app doesn't include an AppBar, title, or background color. If you want these features in a non-Material app, you have to build them yourself. This app changes the background color to white and the text to dark grey to mimic a Material app.

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One of the most common layout patterns is to arrange widgets vertically or horizontally. You can use a Row widget to arrange widgets horizontally, and a Column widget to arrange widgets vertically.

To create a row or column in Flutter, you add a list of children widgets to a Row or Column widget. In turn, each child can itself be a row or column, and so on. The following example shows how it is possible to nest rows or columns inside of rows or columns.

This layout is organized as a Row. The row contains two children: a column on the left, and an image on the right:

The left column's widget tree nests rows and columns.

You'll implement some of Pavlova's layout code in Nesting rows and columns.

Aligning widgets

You control how a row or column aligns its children using the mainAxisAlignment and crossAxisAlignment properties. For a row, the main axis runs horizontally and the cross axis runs vertically. For a column, the main axis runs vertically and the cross axis runs horizontally.

The MainAxisAlignment and CrossAxisAlignment enums offer a variety of constants for controlling alignment.

In the following example, each of the 3 images is 100 pixels wide. The render box (in this case, the entire screen) is more than 300 pixels wide, so setting the main axis alignment to spaceEvenly divides the free horizontal space evenly between, before, and after each image.

            Row(   mainAxisAlignment: MainAxisAlignment.spaceEvenly,   children: [     Image.asset('images/pic1.jpg'),     Image.asset('images/pic2.jpg'),     Image.asset('images/pic3.jpg'),   ], );

Columns work the same way as rows. The following example shows a column of 3 images, each is 100 pixels high. The height of the render box (in this case, the entire screen) is more than 300 pixels, so setting the main axis alignment to spaceEvenly divides the free vertical space evenly between, above, and below each image.

              Column(   mainAxisAlignment: MainAxisAlignment.spaceEvenly,   children: [     Image.asset('images/pic1.jpg'),     Image.asset('images/pic2.jpg'),     Image.asset('images/pic3.jpg'),   ], );

App source: row_column

Sizing widgets

When a layout is too large to fit a device, a yellow and black striped pattern appears along the affected edge. Here is an example of a row that is too wide:

Widgets can be sized to fit within a row or column by using the Expanded widget. To fix the previous example where the row of images is too wide for its render box, wrap each image with an Expanded widget.

Row(   crossAxisAlignment: CrossAxisAlignment.center,   children: [            Expanded(       child: Image.asset('images/pic1.jpg'),     ),            Expanded(       child: Image.asset('images/pic2.jpg'),     ),            Expanded(       child: Image.asset('images/pic3.jpg'),     ),   ], );

Perhaps you want a widget to occupy twice as much space as its siblings. For this, use the Expanded widget flex property, an integer that determines the flex factor for a widget. The default flex factor is 1. The following code sets the flex factor of the middle image to 2:

Row(   crossAxisAlignment: CrossAxisAlignment.center,   children: [     Expanded(       child: Image.asset('images/pic1.jpg'),     ),     Expanded(            flex: 2,            child: Image.asset('images/pic2.jpg'),     ),     Expanded(       child: Image.asset('images/pic3.jpg'),     ),   ], );

Packing widgets

By default, a row or column occupies as much space along its main axis as possible, but if you want to pack the children closely together, set its mainAxisSize to MainAxisSize.min. The following example uses this property to pack the star icons together.

Row(            mainAxisSize: MainAxisSize.min,            children: [     Icon(Icons.star, color: Colors.green[500]),     Icon(Icons.star, color: Colors.green[500]),     Icon(Icons.star, color: Colors.green[500]),     const Icon(Icons.star, color: Colors.black),     const Icon(Icons.star, color: Colors.black),   ], )

Nesting rows and columns

The layout framework allows you to nest rows and columns inside of rows and columns as deeply as you need. Let's look at the code for the outlined section of the following layout:

The outlined section is implemented as two rows. The ratings row contains five stars and the number of reviews. The icons row contains three columns of icons and text.

The widget tree for the ratings row:

The ratings variable creates a row containing a smaller row of 5 star icons, and text:

var stars = Row(   mainAxisSize: MainAxisSize.min,   children: [     Icon(Icons.star, color: Colors.green[500]),     Icon(Icons.star, color: Colors.green[500]),     Icon(Icons.star, color: Colors.green[500]),     const Icon(Icons.star, color: Colors.black),     const Icon(Icons.star, color: Colors.black),   ], );  final            ratings            = Container(   padding: const EdgeInsets.all(20),   child: Row(     mainAxisAlignment: MainAxisAlignment.spaceEvenly,     children: [       stars,       const Text(         '170 Reviews',         style: TextStyle(           color: Colors.black,           fontWeight: FontWeight.w800,           fontFamily: 'Roboto',           letterSpacing: 0.5,           fontSize: 20,         ),       ),     ],   ), );

The icons row, below the ratings row, contains 3 columns; each column contains an icon and two lines of text, as you can see in its widget tree:

The iconList variable defines the icons row:

const descTextStyle = TextStyle(   color: Colors.black,   fontWeight: FontWeight.w800,   fontFamily: 'Roboto',   letterSpacing: 0.5,   fontSize: 18,   height: 2, );  // DefaultTextStyle.merge() allows you to create a default text // style that is inherited by its child and all subsequent children. final            iconList            = DefaultTextStyle.merge(   style: descTextStyle,   child: Container(     padding: const EdgeInsets.all(20),     child: Row(       mainAxisAlignment: MainAxisAlignment.spaceEvenly,       children: [         Column(           children: [             Icon(Icons.kitchen, color: Colors.green[500]),             const Text('PREP:'),             const Text('25 min'),           ],         ),         Column(           children: [             Icon(Icons.timer, color: Colors.green[500]),             const Text('COOK:'),             const Text('1 hr'),           ],         ),         Column(           children: [             Icon(Icons.restaurant, color: Colors.green[500]),             const Text('FEEDS:'),             const Text('4-6'),           ],         ),       ],     ),   ), );

The leftColumn variable contains the ratings and icons rows, as well as the title and text that describes the Pavlova:

final            leftColumn            = Container(   padding: const EdgeInsets.fromLTRB(20, 30, 20, 20),   child: Column(     children: [       titleText,       subTitle,       ratings,       iconList,     ],   ), );

The left column is placed in a SizedBox to constrain its width. Finally, the UI is constructed with the entire row (containing the left column and the image) inside a Card.

The Pavlova image is from Pixabay. You can embed an image from the net using Image.network() but, for this example, the image is saved to an images directory in the project, added to the pubspec file, and accessed using Images.asset(). For more information, see Adding assets and images.

body: Center(   child: Container(     margin: const EdgeInsets.fromLTRB(0, 40, 0, 30),     height: 600,     child: Card(       child: Row(         crossAxisAlignment: CrossAxisAlignment.start,         children: [           SizedBox(             width: 440,             child: leftColumn,           ),           mainImage,         ],       ),     ),   ), ),

App source: pavlova

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Flutter has a rich library of layout widgets. Here are a few of those most commonly used. The intent is to get you up and running as quickly as possible, rather than overwhelm you with a complete list. For information on other available widgets, refer to the Widget catalog, or use the Search box in the API reference docs. Also, the widget pages in the API docs often make suggestions about similar widgets that might better suit your needs.

The following widgets fall into two categories: standard widgets from the widgets library, and specialized widgets from the Material library. Any app can use the widgets library but only Material apps can use the Material Components library.

Standard widgets

• Container: Adds padding, margins, borders, background color, or other decorations to a widget.
• GridView: Lays widgets out as a scrollable grid.
• ListView: Lays widgets out as a scrollable list.
• Stack: Overlaps a widget on top of another.

Material widgets

• Card: Organizes related info into a box with rounded corners and a drop shadow.
• ListTile: Organizes up to 3 lines of text, and optional leading and trailing icons, into a row.

Container

Many layouts make liberal use of Containers to separate widgets using padding, or to add borders or margins. You can change the device's background by placing the entire layout into a Container and changing its background color or image.

Summary (Container)

• Add padding, margins, borders
• Change background color or image
• Contains a single child widget, but that child can be a Row, Column, or even the root of a widget tree

Examples (Container)

This layout consists of a column with two rows, each containing 2 images. A Container is used to change the background color of the column to a lighter grey.

Widget _buildImageColumn() {   return              Container(     decoration: const BoxDecoration(       color: Colors.black26,     ),     child: Column(       children: [         _buildImageRow(1),         _buildImageRow(3),       ],     ),   ); }

A Container is also used to add a rounded border and margins to each image:

Widget _buildDecoratedImage(int imageIndex) => Expanded(       child:            Container(         decoration: BoxDecoration(           border: Border.all(width: 10, color: Colors.black38),           borderRadius: const BorderRadius.all(Radius.circular(8)),         ),         margin: const EdgeInsets.all(4),         child: Image.asset('images/pic$imageIndex.jpg'),       ),     );  Widget _buildImageRow(int imageIndex) => Row(       children: [         _buildDecoratedImage(imageIndex),         _buildDecoratedImage(imageIndex + 1),       ],     );

You can find more Container examples in the tutorial and the Flutter Gallery (running app, repo).

App source: container

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GridView

Use GridView to lay widgets out as a two-dimensional list. GridView provides two pre-fabricated lists, or you can build your own custom grid. When a GridView detects that its contents are too long to fit the render box, it automatically scrolls.

Summary (GridView)

• Lays widgets out in a grid
• Detects when the column content exceeds the render box and automatically provides scrolling
• Build your own custom grid, or use one of the provided grids:
  • GridView.count allows you to specify the number of columns
  • GridView.extent allows you to specify the maximum pixel width of a tile

Examples (GridView)

Uses GridView.extent to create a grid with tiles a maximum 150 pixels wide.

App source: grid_and_list

Uses GridView.count to create a grid that's 2 tiles wide in portrait mode, and 3 tiles wide in landscape mode. The titles are created by setting the footer property for each GridTile.

Dart code: grid_list_demo.dart from the Flutter Gallery

Widget _buildGrid() =>            GridView.extent(     maxCrossAxisExtent: 150,     padding: const EdgeInsets.all(4),     mainAxisSpacing: 4,     crossAxisSpacing: 4,     children: _buildGridTileList(30));  // The images are saved with names pic0.jpg, pic1.jpg...pic29.jpg. // The List.generate() constructor allows an easy way to create // a list when objects have a predictable naming pattern. List<Container> _buildGridTileList(int count) => List.generate(     count, (i) => Container(child: Image.asset('images/pic$i.jpg')));

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ListView

ListView, a column-like widget, automatically provides scrolling when its content is too long for its render box.

Summary (ListView)

• A specialized Column for organizing a list of boxes
• Can be laid out horizontally or vertically
• Detects when its content won't fit and provides scrolling
• Less configurable than Column, but easier to use and supports scrolling

Examples (ListView)

Uses ListView to display a list of businesses using ListTiles. A Divider separates the theaters from the restaurants.

App source: grid_and_list

Widget _buildList() {   return            ListView(     children: [       _tile('CineArts at the Empire', '85 W Portal Ave', Icons.theaters),       _tile('The Castro Theater', '429 Castro St', Icons.theaters),       _tile('Alamo Drafthouse Cinema', '2550 Mission St', Icons.theaters),       _tile('Roxie Theater', '3117 16th St', Icons.theaters),       _tile('United Artists Stonestown Twin', '501 Buckingham Way',           Icons.theaters),       _tile('AMC Metreon 16', '135 4th St #3000', Icons.theaters),       const Divider(),       _tile('K\'s Kitchen', '757 Monterey Blvd', Icons.restaurant),       _tile('Emmy\'s Restaurant', '1923 Ocean Ave', Icons.restaurant),       _tile(           'Chaiya Thai Restaurant', '272 Claremont Blvd', Icons.restaurant),       _tile('La Ciccia', '291 30th St', Icons.restaurant),     ],   ); }  ListTile _tile(String title, String subtitle, IconData icon) {   return ListTile(     title: Text(title,         style: const TextStyle(           fontWeight: FontWeight.w500,           fontSize: 20,         )),     subtitle: Text(subtitle),     leading: Icon(       icon,       color: Colors.blue[500],     ),   ); }

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Stack

Use Stack to arrange widgets on top of a base widget—often an image. The widgets can completely or partially overlap the base widget.

Summary (Stack)

• Use for widgets that overlap another widget
• The first widget in the list of children is the base widget; subsequent children are overlaid on top of that base widget
• A Stack's content can't scroll
• You can choose to clip children that exceed the render box

Examples (Stack)

Uses Stack to overlay a Container (that displays its Text on a translucent black background) on top of a CircleAvatar. The Stack offsets the text using the alignment property and Alignments.

App source: card_and_stack

Widget _buildStack() {   return            Stack(     alignment: const Alignment(0.6, 0.6),     children: [       const CircleAvatar(         backgroundImage: AssetImage('images/pic.jpg'),         radius: 100,       ),       Container(         decoration: const BoxDecoration(           color: Colors.black45,         ),         child: const Text(           'Mia B',           style: TextStyle(             fontSize: 20,             fontWeight: FontWeight.bold,             color: Colors.white,           ),         ),       ),     ],   ); }

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Card

A Card, from the Material library, contains related nuggets of information and can be composed from almost any widget, but is often used with ListTile. Card has a single child, but its child can be a column, row, list, grid, or other widget that supports multiple children. By default, a Card shrinks its size to 0 by 0 pixels. You can use SizedBox to constrain the size of a card.

In Flutter, a Card features slightly rounded corners and a drop shadow, giving it a 3D effect. Changing a Card's elevation property allows you to control the drop shadow effect. Setting the elevation to 24, for example, visually lifts the Card further from the surface and causes the shadow to become more dispersed. For a list of supported elevation values, see Elevation in the Material guidelines. Specifying an unsupported value disables the drop shadow entirely.

Summary (Card)

• Implements a Material card
• Used for presenting related nuggets of information
• Accepts a single child, but that child can be a Row, Column, or other widget that holds a list of children
• Displayed with rounded corners and a drop shadow
• A Card's content can't scroll
• From the Material library

Examples (Card)

A Card containing 3 ListTiles and sized by wrapping it with a SizedBox. A Divider separates the first and second ListTiles.

App source: card_and_stack

Widget _buildCard() {   return SizedBox(     height: 210,     child:            Card(       child: Column(         children: [           ListTile(             title: const Text(               '1625 Main Street',               style: TextStyle(fontWeight: FontWeight.w500),             ),             subtitle: const Text('My City, CA 99984'),             leading: Icon(               Icons.restaurant_menu,               color: Colors.blue[500],             ),           ),           const Divider(),           ListTile(             title: const Text(               '(408) 555-1212',               style: TextStyle(fontWeight: FontWeight.w500),             ),             leading: Icon(               Icons.contact_phone,               color: Colors.blue[500],             ),           ),           ListTile(             title: const Text('costa@example.com'),             leading: Icon(               Icons.contact_mail,               color: Colors.blue[500],             ),           ),         ],       ),     ),   ); }

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ListTile

Use ListTile, a specialized row widget from the Material library, for an easy way to create a row containing up to 3 lines of text and optional leading and trailing icons. ListTile is most commonly used in Card or ListView, but can be used elsewhere.

Summary (ListTile)

• A specialized row that contains up to 3 lines of text and optional icons
• Less configurable than Row, but easier to use
• From the Material library

Examples (ListTile)

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Constraints

To fully understand Flutter's layout system, you need to learn how Flutter positions and sizes the components in a layout. For more information, see Understanding constraints.

Videos

The following videos, part of the Flutter in Focus series, explain Stateless and Stateful widgets.

Flutter in Focus playlist

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Each episode of the Widget of the Week series focuses on a widget. Several of them includes layout widgets.

Flutter Widget of the Week playlist

Other resources

The following resources might help when writing layout code.

• Layout tutorial

  Learn how to build a layout.

• Widget catalog

  Describes many of the widgets available in Flutter.

• HTML/CSS Analogs in Flutter

  For those familiar with web programming, this page maps HTML/CSS functionality to Flutter features.

• Flutter Gallery running app, repo

  Demo app showcasing many Material Design widgets and other Flutter features.

• API reference docs

  Reference documentation for all of the Flutter libraries.

• Dealing with Box Constraints in Flutter

  Discusses how widgets are constrained by their render boxes.

• Adding assets and images

  Explains how to add images and other assets to your app's package.

• Zero to One with Flutter

  One person's experience writing his first Flutter app.

currylikedy.blogspot.com

Source: https://docs.flutter.dev/development/ui/layout

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