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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,
),
),
),
);
}
}<code_end>
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.That’s it! When you run the app, you should see Hello World.App source code:<topic_end>
<topic_start>
Lay out multiple widgets vertically and horizontally
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.<topic_end>
<topic_start>What's the point?
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.info Note
Row and Column are basic primitive widgets for horizontal
and vertical layouts—these low-level widgets allow for maximum
customization. Flutter also offers specialized, higher level widgets
that might be sufficient for your needs. For example,
instead of Row you might prefer ListTile,
an easy-to-use widget with properties for leading and trailing icons,
and up to 3 lines of text. Instead of Column, you might prefer
ListView, a column-like layout that automatically scrolls
if its content is too long to fit the available space.
For more information, see Common layout widgets.<topic_end>
<topic_start>
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.info Note
When you add images to your project,
you need to update the pubspec.yaml file to access
them—this example uses Image.asset to display
the images. For more information, see this example’s
pubspec.yaml file or Adding assets and images.
You don’t need to do this if you’re referencing online
images using Image.network.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.App source: row_columnColumns 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.App source: row_column<topic_end>
<topic_start>
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.App source: sizingPerhaps 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:App source: sizing<topic_end>
<topic_start>
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.App source: pavlova<topic_end>
<topic_start>
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:
<code_start>final 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]),