web-analogs.md

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page	Flutter for Web (HTML/CSS) Developers	/web-analogs/

Contents:

• TOC Placeholder {:toc}

This page is for users who are familiar with the HTML and CSS syntax for arranging components of an application's UI. It maps HTML/CSS code snippets to their Flutter/Dart code equivalents.

The examples assume:

• The HTML document starts with a modern HTML DOCTYPE, and the CSS box model for all HTML elements is set to border-box, for consistency with the Flutter model. {% prettify css %}

  { box-sizing: border-box; } {% endprettify %}

• In Flutter, the default styling of the "Lorem ipsum" text is defined by the bold24Roboto variable as follows, to keep the syntax simple: {% prettify dart %} TextStyle bold24Roboto = new TextStyle( color: Colors.white, fontSize: 24.0, fontWeight: FontWeight.w900, ); {% endprettify %}

Performing basic layout operations

The following examples show how to perform the most common UI layout tasks.

Styling and aligning text

Font style, size, and other text attributes that CSS handles with the font and color properties are individual properties of a TextStyle child of a Text widget.

In both HTML and Flutter, child elements or widgets are anchored at the top left, by default.

{% prettify css %}

Lorem ipsum

.greybox { background-color: #e0e0e0; /* grey 300 */ width: 320px; height: 240px; [[highlight]] font: 900 24px Georgia;[[/highlight]] } {% endprettify %}

{% prettify dart %} var container = new Container( // grey box child: new Text( "Lorem ipsum", style: [[highlight]]new TextStyle( fontSize: 24.0 fontWeight: FontWeight.w900, fontFamily: "Georgia", ),[[/highlight]] ), width: 320.0, height: 240.0, color: Colors.grey[300], ); {% endprettify %}

Setting background color

In Flutter, you set the background color using a Container’s decoration property.

The CSS examples use the hex color equivalents to the Material color palette.

{% prettify css %}

Lorem ipsum

.greybox { [[highlight]] background-color: #e0e0e0; [[/highlight]] /* grey 300 */ width: 320px; height: 240px; font: 900 24px Roboto; } {% endprettify %}

{% prettify dart %} var container = new Container( // grey box child: new Text( "Lorem ipsum", style: bold24Roboto, ), width: 320.0, height: 240.0, [[highlight]] color: Colors.grey[300],[[/highlight]] ); {% endprettify %}

Centering components

A Center widget centers its child both horizontally and vertically.

To accomplish a similar effect in CSS, the parent element uses either a flex or table-cell display behavior. The examples on this page show the flex behavior.

{% prettify css %}

Lorem ipsum

.greybox { background-color: #e0e0e0; /* grey 300 */ width: 320px; height: 240px; font: 900 24px Roboto; [[highlight]] display: flex; align-items: center; justify-content: center; [[/highlight]] } {% endprettify %}

{% prettify dart %} var container = new Container( // grey box child: [[highlight]] new Center( child: [[/highlight]] new Text( "Lorem ipsum", style: bold24Roboto, ), ), width: 320.0, height: 240.0, color: Colors.grey[300], ); {% endprettify %}

Setting container width

To specify the width of a Container widget, its width property. This is a fixed width, unlike the CSS max-width property that adjusts the container width up to a maximum value. To mimic that effect in Flutter, use the constraints property of the Container. Create a new BoxConstraints widget with a minWidth or maxWidth.

For nested Containers, if the parent’s width is less than the child’s width, the child Container sizes itself to match the parent.

{% prettify css %}

Lorem ipsum

.greybox { background-color: #e0e0e0; /* grey 300 / [[highlight]] width: 320px; [[/highlight]] height: 240px; font: 900 24px Roboto; display: flex; align-items: center; justify-content: center; } .redbox { background-color: #ef5350; / red 400 */ padding: 16px; color: #ffffff; [[highlight]] width: 100%; max-width: 240px; [[/highlight]] } {% endprettify %}

{% prettify dart %} var container = new Container( // grey box child: new Center( child: new Container( // red box child: new Text( "Lorem ipsum", style: bold24Roboto, ), decoration: new BoxDecoration( color: Colors.red[400], ), padding: new EdgeInsets.all(16.0), [[highlight]] width: 240.0, [[/highlight]]//max-width is 240.0 ), ), [[highlight]] width: 320.0, [[/highlight]] height: 240.0, color: Colors.grey[300], ); {% endprettify %}

Manipulating position and size

The following examples show how to perform more complex operations on widget position, size, and background.

Setting absolute position

By default, widgets are positioned relative to their parent.

To specify an absolute position for a widget as x-y coordinates, nest it in a Positioned widget that is, in turn, nested in a Stack widget.

{% prettify css %}

Lorem ipsum

.greybox { background-color: #e0e0e0; /* grey 300 / width: 320px; height: 240px; font: 900 24px Roboto; [[highlight]] position: relative; [[/highlight]] } .redbox { background-color: #ef5350; / red 400 */ padding: 16px; color: #ffffff; [[highlight]] position: absolute; top: 24px; left: 24px; [[/highlight]] } {% endprettify %}

{% prettify dart %} var container = new Container( // grey box [[highlight]] child: new Stack( children: [ new Positioned( // red box child: [[/highlight]] new Container( child: new Text( "Lorem ipsum", style: bold24Roboto, ), decoration: new BoxDecoration( color: Colors.red[400], ), padding: new EdgeInsets.all(16.0), ), [[highlight]] left: 24.0, top: 24.0, ), ], ), [[/highlight]] width: 320.0, height: 240.0, color: Colors.grey[300], ); {% endprettify %}

Rotating components

To rotate a widget, nest it in a Transform widget. Use the Transform widget’s alignment and origin properties to specify the transform origin (fulcrum) in relative and absolute terms, respectively.

For a simple 2D rotation, the widget is rotated on the Z axis using radians. (degrees × π / 180)

{% prettify css %}

Lorem ipsum

.greybox { background-color: #e0e0e0; /* grey 300 / width: 320px; height: 240px; font: 900 24px Roboto; display: flex; align-items: center; justify-content: center; } .redbox { background-color: #ef5350; / red 400 */ padding: 16px; color: #ffffff; [[highlight]] transform: rotate(15deg); [[/highlight]] } {% endprettify %}

{% prettify dart %} var container = new Container( // gray box child: new Center( child: [[highlight]] new Transform( child: [[/highlight]] new Container( // red box child: new Text( "Lorem ipsum", style: bold24Roboto, textAlign: TextAlign.center, ), decoration: new BoxDecoration( color: Colors.red[400], ), padding: new EdgeInsets.all(16.0), ), [[highlight]] alignment: Alignment.center, transform: new Matrix4.identity() ..rotateZ(15 * 3.1415927 / 180), ), [[/highlight]] ), width: 320.0, height: 240.0, color: Colors.grey[300], ); {% endprettify %}

Scaling components

To scale a widget up or down, nest it in a Transform widget. Use the Transform widget’s alignment and origin properties to specify the transform origin (fulcrum) in relative or absolute terms, respectively.

For a simple scaling operation along the x-axis, create a new Matrix4 identity object and use its scale() method to specify the scaling factor.

When you scale a parent widget, its child widgets are scaled accordingly.

{% prettify css %}

Lorem ipsum

.greybox { background-color: #e0e0e0; /* grey 300 / width: 320px; height: 240px; font: 900 24px Roboto; display: flex; align-items: center; justify-content: center; } .redbox { background-color: #ef5350; / red 400 */ padding: 16px; color: #ffffff; [[highlight]] transform: scale(1.5); [[/highlight]] } {% endprettify %}

{% prettify dart %} var container = new Container( // gray box child: new Center( child: [[highlight]] new Transform( child: [[/highlight]] new Container( // red box child: new Text( "Lorem ipsum", style: bold24Roboto, textAlign: TextAlign.center, ), decoration: new BoxDecoration( color: Colors.red[400], ), padding: new EdgeInsets.all(16.0), ), [[highlight]] alignment: Alignment.center, transform: new Matrix4.identity() ..scale(1.5), ), [[/highlight]] width: 320.0, height: 240.0, color: Colors.grey[300], ); {% endprettify %}

Applying a linear gradient

To apply a linear gradient to a widget's background, nest it in a Container widget. Then use the Container widget’s decoration property to create a BoxDecoration object, and use BoxDecoration's gradient property to transform the background fill.

The gradient “angle” is based on the Alignment (x, y) values:

• If the beginning and ending x values are equal, the gradient is vertical (0° | 180°).
• If the beginning and ending y values are equal, the gradient is horizontal (90° | 270°).

Vertical Gradient

{% prettify css %}

Lorem ipsum

.greybox { background-color: #e0e0e0; /* grey 300 */ width: 320px; height: 240px; font: 900 24px Roboto; display: flex; align-items: center; justify-content: center; } .redbox { padding: 16px; color: #ffffff; [[highlight]] background: linear-gradient(180deg, #ef5350, rgba(0, 0, 0, 0) 80%); [[/highlight]] } {% endprettify %}

{% prettify dart %} var container = new Container( // grey box child: new Center( child: new Container( // red box child: new Text( "Lorem ipsum", style: bold24Roboto, ), [[highlight]] decoration: new BoxDecoration( gradient: new LinearGradient( begin: const Alignment(0.0, -1.0), end: const Alignment(0.0, 0.6), colors: [ const Color(0xffef5350), const Color(0x00ef5350) ], ), ), [[/highlight]] padding: new EdgeInsets.all(16.0), ), ), width: 320.0, height: 240.0, color: Colors.grey[300], ); {% endprettify %}

Horizontal gradient

{% prettify css %}

Lorem ipsum

.greybox { background-color: #e0e0e0; /* grey 300 */ width: 320px; height: 240px; font: 900 24px Roboto; display: flex; align-items: center; justify-content: center; } .redbox { padding: 16px; color: #ffffff; [[highlight]] background: linear-gradient(90deg, #ef5350, rgba(0, 0, 0, 0) 80%); [[/highlight]] } {% endprettify %}

{% prettify dart %} var container = new Container( // grey box child: new Center( child: new Container( // red box child: new Text( "Lorem ipsum", style: bold24Roboto, ), [[highlight]] decoration: new BoxDecoration( gradient: new LinearGradient( begin: const Alignment(-1.0, 0.0), end: const Alignment(0.6, 0.0), colors: [ const Color(0xffef5350), const Color(0x00ef5350) ], ), ), [[/highlight]] padding: new EdgeInsets.all(16.0), ), ), width: 320.0, height: 240.0, color: Colors.grey[300], ); {% endprettify %}

Manipulating shapes

The following examples show how to make and customize shapes.

Rounding corners

To round the corners of a rectangular shape, use the borderRadius property of a BoxDecoration object. Create a new BorderRadius object that specifies the radii for rounding each corner.

{% prettify css %}

Lorem ipsum

.greybox { background-color: #e0e0e0; /* gray 300 / width: 320px; height: 240px; font: 900 24px Roboto; display: flex; align-items: center; justify-content: center; } .redbox { background-color: #ef5350; / red 400 */ padding: 16px; color: #ffffff; [[highlight]] border-radius: 8px; [[/highlight]] } {% endprettify %}

{% prettify dart %} var container = new Container( // grey box child: new Center( child: new Container( // red circle child: new Text( "Lorem ipsum", style: bold24Roboto, ), decoration: new BoxDecoration( color: Colors.red[400], [[highlight]] borderRadius: new BorderRadius.all( const Radius.circular(8.0), ), [[/highlight]] ), padding: new EdgeInsets.all(16.0), ), ), width: 320.0, height: 240.0, color: Colors.grey[300], ); {% endprettify %}

Adding box shadows

In CSS you can specify shadow offset and blur in shorthand, using the box-shadow property. This example shows two box shadows, with properties:

• xOffset: 0px, yOffset: 2px, blur: 4px, color: black @80% alpha
• xOffset: 0px, yOffset: 06x, blur: 20px, color: black @50% alpha

In Flutter, each property and value is specified separately. Use the boxShadow property of BoxDecoration to create a list of BoxShadow widgets. You can define one or multiple BoxShadow widgets, which can be stacked to customize the shadow depth, color, etc.

{% prettify css %}

Lorem ipsum

.greybox { background-color: #e0e0e0; /* grey 300 / width: 320px; height: 240px; font: 900 24px Roboto; display: flex; align-items: center; justify-content: center; } .redbox { background-color: #ef5350; / red 400 */ padding: 16px; color: #ffffff; [[highlight]] box-shadow: 0 2px 4px rgba(0, 0, 0, 0.8), 0 6px 20px rgba(0, 0, 0, 0.5);[[/highlight]] } {% endprettify %}

{% prettify dart %} var container = new Container( // grey box child: new Center( child: new Container( // red box child: new Text( "Lorem ipsum", style: bold24Roboto, ), decoration: new BoxDecoration( color: Colors.red[400], [[highlight]] boxShadow: [ new BoxShadow ( color: const Color(0xcc000000), offset: new Offset(0.0, 2.0), blurRadius: 4.0, ), new BoxShadow ( color: const Color(0x80000000), offset: new Offset(0.0, 6.0), blurRadius: 20.0, ), ], [[/highlight]] ), padding: new EdgeInsets.all(16.0), ), ), width: 320.0, height: 240.0, decoration: new BoxDecoration( color: Colors.grey[300], ), margin: new EdgeInsets.only(bottom: 16.0), ); {% endprettify %}

Making circles and ellipses

Making a circle in CSS requires a workaround of applying a border-radius of 50% to all four sides of a rectangle, though there are basic shapes.

While this approach is supported with the borderRadius property of BoxDecoration, Flutter provides a shape property with BoxShape enum for this purpose.

{% prettify css %}

Lorem ipsum

.greybox { background-color: #e0e0e0; /* gray 300 / width: 320px; height: 240px; font: 900 24px Roboto; display: flex; align-items: center; justify-content: center; } .redcircle { background-color: #ef5350; / red 400 */ padding: 16px; color: #ffffff; [[highlight]] text-align: center; width: 160px; height: 160px; border-radius: 50%; [[/highlight]] } {% endprettify %}

{% prettify dart %} var container = new Container( // grey box child: new Center( child: new Container( // red circle child: new Text( "Lorem ipsum", style: bold24Roboto, [[highlight]] textAlign: TextAlign.center, [[/highlight]] ), decoration: new BoxDecoration( color: Colors.red[400], [[highlight]] shape: BoxShape.circle, [[/highlight]] ), padding: new EdgeInsets.all(16.0), [[highlight]] width: 160.0, height: 160.0, [[/highlight]] ), ), width: 320.0, height: 240.0, color: Colors.grey[300], ); {% endprettify %}

Manipulating text

The following examples show how to specify fonts and other text attributes. They also show how to transform text strings, customize spacing, and create excerpts.

Adjusting text spacing

In CSS you specify the amount of white space between each letter or word by giving a length value for the letter-spacing and word-spacing properties, respectively. The amount of space can be in px, pt, cm, em, etc.

In Flutter, you specify white space as logical pixels (negative values are allowed) for the letterSpacing and wordSpacing properties of a TextStyle child of a Text widget.

{% prettify css %}

Lorem ipsum

.greybox { background-color: #e0e0e0; /* grey 300 / width: 320px; height: 240px; font: 900 24px Roboto; display: flex; align-items: center; justify-content: center; } .redbox { background-color: #ef5350; / red 400 */ padding: 16px; color: #ffffff; [[highlight]] letter-spacing: 4px; [[/highlight]] } {% endprettify %}

{% prettify dart %} var container = new Container( // grey box child: new Center( child: new Container( // red box child: new Text( "Lorem ipsum", style: new TextStyle( color: Colors.white, fontSize: 24.0, fontWeight: FontWeight.w900, [[highlight]] letterSpacing: 4.0, [[/highlight]] ), ), decoration: new BoxDecoration( color: Colors.red[400], ), padding: new EdgeInsets.all(16.0), ), ), width: 320.0, height: 240.0, color: Colors.grey[300], ); {% endprettify %}

Making inline formatting changes

A Text widget lets you display text with the same formatting characteristics. To display text that uses multiple styles (in this example, a single word with emphasis), use a RichText widget instead. Its text property can specify one or more TextSpan widgets that can be individually styled.

In the following example, "Lorem" is in a TextSpan widget with the default (inherited) text styling, and "ipsum" is in a separate TextSpan with custom styling.

{% prettify css %}

[[highlight]] Lorem ipsum [[/highlight]]

.greybox { background-color: #e0e0e0; /* grey 300 / width: 320px; height: 240px; [[highlight]] font: 900 24px Roboto; [[/highlight]] display: flex; align-items: center; justify-content: center; } .redbox { background-color: #ef5350; / red 400 */ padding: 16px; color: #ffffff; } [[highlight]] .redbox em { font: 300 48px Roboto; font-style: italic; } [[/highlight]] {% endprettify %}

{% prettify dart %} var container = new Container( // grey box child: new Center( child: new Container( // red box child: [[highlight]] new RichText( text: new TextSpan( style: bold24Roboto, children: [ new TextSpan(text: "Lorem "), new TextSpan( text: "ipsum", style: new TextStyle( fontWeight: FontWeight.w300, fontStyle: FontStyle.italic, fontSize: 48.0, ), ), ], ), ), [[/highlight]] decoration: new BoxDecoration( backgroundColor: Colors.red[400], ), padding: new EdgeInsets.all(16.0), ), ), width: 320.0, height: 240.0, color: Colors.grey[300], ); {% endprettify %}

Creating text excerpts

An excerpt displays the initial line(s) of text in a paragraph, and handles the overflow text, often using an ellipsis. In HTML/CSS an excerpt can be no longer than one line. Truncating after multiple lines requires some JavaScript code.

In Flutter, use the maxLines property of a Text widget to specify the number of lines to include in the excerpt, and the overflow property for handling overflow text.

{% prettify css %}

Lorem ipsum dolor sit amet, consec etur

.greybox { background-color: #e0e0e0; /* grey 300 / width: 320px; height: 240px; font: 900 24px Roboto; display: flex; align-items: center; justify-content: center; } .redbox { background-color: #ef5350; / red 400 */ padding: 16px; color: #ffffff; [[highlight]] overflow: hidden; text-overflow: ellipsis; white-space: nowrap; [[/highlight]] } {% endprettify %}

{% prettify dart %} var container = new Container( // grey box child: new Center( child: new Container( // red box child: new Text( "Lorem ipsum dolor sit amet, consec etur", style: bold24Roboto, [[highlight]] overflow: TextOverflow.ellipsis, maxLines: 1, [[/highlight]] ), decoration: new BoxDecoration( backgroundColor: Colors.red[400], ), padding: new EdgeInsets.all(16.0), ), ), width: 320.0, height: 240.0, color: Colors.grey[300], ); {% endprettify %}