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Thomas Burleson edited this page Dec 15, 2016 · 49 revisions

Flex Layout

Angular Flex Layout provides a sophisticated layout API using FlexBox CSS + mediaQuery. This module provides Angular developers with component layout features using a custom Layout API, mediaQuery observables,and injected DOM flexbox-2016 css stylings.

The Layout engine intelligently automates the process of applying appropriate FlexBox CSS to browser view hierarchies. This automation also addresses many of the complexities and workarounds encountered with the traditional, manual, CSS-only application of Flexbox CSS.

css3-flexbox-model

The Angular Flexbox Layout features enable developers to organize UI page elements in row and column structures with alignments, resizing, and padding. These layouts can be nested and easily used with hierarchical DOM structures. Since the Layout applies/injects Flexbox CSS, DOM elements will fluidly update their positioning and sizes as the viewport size changes.

<div class="flex-container" fx-layout="row" fx-layout-align="center center">
  <div class="flex-item"></div>
  <div class="flex-item"></div>
  <div class="flex-item"></div>
</div>

The above Flex Layout usages do not require any external stylesheets nor any custom CSS programming. The Angular directives do all the work of magically setting the flexbox css.

Integrating mediaQuery features into the Layout engine enables the API to be Responsive: DOM elements can adjust layout-directions, visibility, and sizing constraints based on specific viewport sizes such as desktop or mobile devices.

Angular Flex Layout is a pure-Typescript Layout engine; unlike the pure CSS-only implementations published in other Flexbox libraries and the JS+CSS implementation of Angular Material v1.x Layouts.

  • This implementation of Flex Layouts is independent of Angular Material (v1 or v2).
  • This implementation is currently only available for Angular applications.

Useful Resources

  • Getting Started
  • Fast Start with Builds
  • Using Flex-Layout with Angular CLI

API Overview

The Flex Layout features provide smart, syntactic directives to allow developers to easily and intuitively create responsive and adaptive layouts using Flexbox CSS. The public Layout API is a simply list of HTML attributes that can be used on HTML containers and elements:

HTML Markup API Allowed values (raw or interpolated)
fx-layout `row
fx-layout-wrap `""
fx-layout-align `start
fx-flex "" , px , %
fx-flex-fill
fx-flex-order int
fx-flex-offset %, px
fx-flex-align `start

Static Markup Example:

<div fx-layout='column' class="zero">

  <div fx-flex="33"                          class="one" ></div>
  <div fx-flex="33%" [fx-layout]="direction" class="two">

    <div fx-flex="22%"    class="two_one"></div>
    <div fx-flex="205px"  class="two_two"></div>
    <div fx-flex="30"     class="two_three"></div>

  </div>
  <div fx-flex class="three"></div>

</div>

Flex Layout directives assign CSS styles directly in-line to the host element. These in-line styles override inherited styles, ShadowDOM styles and even ShadowDOM tree stylings on the element :host

Responsive Features

To extend the static API with responsive features, we first associate specific breakpoint aliases with mediaQuery values. And if we use Breakpoints as specified by Material Design:


We can associate breakpoints with mediaQuery definitions using breakpoint alias(es):

breakpoint mediaQuery
"" 'screen'
xs 'screen and (max-width: 599px)'
gt-xs 'screen and (min-width: 600px)'
sm 'screen and (min-width: 600px) and (max-width: 959px)'
gt-sm 'screen and (min-width: 960px)'
md 'screen and (min-width: 960px) and (max-width: 1279px)'
gt-md 'screen and (min-width: 1280px)'
lg 'screen and (min-width: 1280px) and (max-width: 1919px)'
gt-lg 'screen and (min-width: 1920px)'
xl 'screen and (min-width: 1920px)'

If we combine the breakpoint alias with the Layout API we can easily support Responsive breakpoints with a simple markup convention: the alias is used as suffix extensions to the Layout API:

<api>.<breakpoint alias>='<value>'

Below is an example usage of the Responsive Layout API:

<div fx-layout='column' class="zero">

  <div fx-flex="33" [fx-flex.md]="box1Width" class="one" ></div>
  <div fx-flex="33" [fx-layout]="direction" layout.md="row" class="two">

    <div fx-flex="22"    fx-flex.md="10px" fx-hide.lg                       class="two_one"></div>
    <div fx-flex="205"   fx-flex.md="65"                                    class="two_two"></div>
    <div fx-flex="30px"  fx-flex.md="25"   fx-show [fx-hide.md]="hideBox"   class="two_three"></div>

  </div>
  <div fx-flex class="three"></div>

</div>

In the markup above the layout directives use both static values and expression bindings; where the values are expressed as raw, percentage, or pixel values.

Implementation

The Angular 2 architecture for Layouts eliminates all external Flexbox stylesheets and SCSS files formerly used in the Angular Material 1 Layout implementations. This is pure typescript- Angular Layout engine that is independent of Angular Material yet can be used easily within any Material 2 application.

The Layout API directives are used to create DOM element style injectors which inject specific, custom Flexbox CSS directly as inline styles onto the DOM element.

For example, consider the use of the fx-layout="row" and fx-layout-align="center center" directives.

Static Markup:

<div [fx-layout]="direction" fx-layout-align="center center">
  <div>one</div>
  <div>two</div>
  <div>three</div>
</div>

is transformed with inline, injected styles:

<div fx-layout="row" fx-layout-align="center center"
      style="display: flex; flex-direction: row; max-width: 100%; box-sizing: border-box; justify-content: center; align-content: center; align-items: center;">
  <div>one</div>
  <div>two</div>
  <div>three</div>
</div>

ng2layouts_classdiagram

Adaptive Layouts (future)

Different from responsive layouts where components change sizes and positions, the concepts of Adaptive layouts provide for UX where different components may be used for different breakpoints.

Animations can also be extended to support MediaQuery activations: different animations will run for different viewport sizes.

Developers can use the following:

  • fx-hide
  • fx-show
  • ngIf

This will be documented more before release 1.

Summary

Compared to the Layout API in Angular Material v1.x, this codebase easier to maintain and debug, other more important benefits have been realized:

  • Independent of Angular Material
  • No external CSS requirements
  • Use provider to supply custom breakpoints
  • Notifications for breakpoints changes
  • Includes workaround for MediaQuery issues with overlapping breakpoints
  • Support (future) for Handset/Tablet and Orientation breakpoints
  • Support for ANY Layout injector value (instead of increments for 5)
  • Change detection for Layout injector values
  • MediaQuery Activation detection
  • Support for raw values or interpolated values
  • Support for raw, percentage or px-suffix values

Use Cases

Below are the use cases address by this Layout library. These will be detailed in a separate design doc (pending). The current implementation, however, provides features/solutions for all listed user cases.

Non-responsive Use Cases:
  • Layout elements in rows
  • Layout elements in columns
  • Nested containers should have isolated layout constraints
  • Adjust container children sizes (flex) based on static percentages
  • Adjust container children sizes (flex) based on static pixel values
  • Adjust container children sizes (flex) based on expressions
  • Adjust alignment of container children based on static/dynamic values
  • Adjust offset of container children based on static/dynamic values
  • Adjust ordering of container children based on static/dynamic values
  • Container children resizing (flex) is dependent upon container layout directions (layout)
  • Changes in Layout directives will update nested Flex children
Responsive API Use Cases:
  • Change Detection: ngOnChanges due to Layout attribute expressions only trigger for defined activated breakpoints or used as fallback
    • Input changes are filtered so the default input key is used if the activation key is not defined
    • Input changes are filtered so only the current activated input change will trigger an update
  • Activations: when the mediaQuery becomes active
    • mq Activation only uses expressions for the activated breakpoint
    • mq Activation fallback to use to non-responsive expressions (fallback) if no breakpoint defined
  • Subscription notifications: using OnMediaQueryChanges
    • Components implementing OnMediaQueryChanges will be notified for each activation (pending)
    • ngOnMediaQueryChanges() uses MediaQueryChanges event arguments
    • MediaQueryChanges will contain the previous activation (and expression value) and the current
  • Querying: for imperative or template logic
    • Components can use MediaQueries::observe() to subscribe to all activations [for imperative actions]
    • Component templates can use $mdMedia.isActive(<query_alias>)
  • Breakpoint Customization:
    • Custom set of breakpoints can be defined as a Provider
    • Custom breakpoints will override ALL default breakpoints (no merging)

                   -   API Documentation   -   StackBlitz Template   -   Live Demos

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