BreakPoints

The token BREAKPOINTS is an injection token in @angular/flex-layout that is used to build a Provider for a raw list of breakpoints.

import {InjectionToken, NgModule} from '@angular/core';
import {BREAKPOINTS, DEFAULT_BREAKPOINTS} from '@angular/flex-layout';

export const BreakPointsProvider = { 
  provide: BREAKPOINTS,
  useValue: DEFAULT_BREAKPOINTS
};

@NgModule({
  providers: [
    BreakPointsProvider,     // Supports developer overrides of list of known breakpoints
 // BreakPointRegistry,      // Registry of known/used BreakPoint(s)
 // MatchMedia,              // Low-level service to publish observables w/ window.matchMedia()
 // MediaMonitor,            // MediaQuery monitor service observes all known breakpoints
 // ObservableMediaProvider  // easy subscription injectable `media$` matchMedia observable
  ]
})
export class CoreModule {
}

This provider is used to return a list to all known BreakPoint(s)... and, in turn, this list is used internally to register mediaQueries and announce mediaQuery activations.

Custom BreakPoints

Using the BREAKPOINTS InjectionToken, developers can add custom breakpoints or easily override existing breakpoints.

For example to add mediaQueries that activate when printing:

custom-breakpoints.ts

import {BREAKPOINTS, DEFAULT_BREAKPOINTS} from '@angular/flex-layout';

const PRINT_BREAKPOINTS = [{
  alias: 'xs.print',
  suffix: 'XsPrint',
  mediaQuery: 'print and (max-width: 297px)',
  overlapping: false
}];

export const CustomBreakPointsProvider = { 
  provide: BREAKPOINTS,
  useValue: [...DEFAULT_BREAKPOINTS, ...PRINT_BREAKPOINTS]
};

my-app-module.ts

import {CommonModule, NgModule} from '@angular/core';
import {FlexLayoutModule} from '@angular/flex-layout';
import {CustomBreakPointsProvider} from 'custom-breakpoints.ts';

@NgModule({
  imports : [
    CommonModule,
    FlexLayoutModule,
  ],
  providers: [
    CustomBreakPointsProvider,     // Adds breakpoints for 'print' mediaQueries
  ]
})
export class MyAppModule {
}

With the above changes, when printing on mobile-sized viewports the xs.print mediaQuery will activate.

Custom Breakpoints and Directives

It must be noted that simply registering custom breakpoints will not automatically mean that Flex-Layout API will support those as selectors.

In the above example the custom Breakpoint has been registered, but HTML selectors for xs.print will not work automatically. Consider the scenario below where some content should be hidden while printing and other content has different layouts while printing:

<section 
    class="main" 
    fxShow 
    fxHide.xs.print="true"> 
 ... 
</section>

<footer 
    fxLayout="row" 
    fxLayout.xs.print="column"> 
 ... 
</section>

Notice the use of 'xs.print' alias in the selectors above

To enable these custom, responsive selectors, developers must extend the ShowHideDirective and the LayoutDirective as follows.

import {Directive, ElementRef, Input, Renderer2} from '@angular/core';
import {ShowHideDirective, MediaMonitor, negativeOf} from '@angular/flex-layout';

@Directive({
  selector: `[fxHide.xs.print]`
})
export class CustomShowHideDirective extends ShowHideDirective {
  constructor(monitor: MediaMonitor, elRef: ElementRef, renderer: Renderer2) {
    super(monitor, elRef, renderer);
  }

  @Input('fxHide.xs.print')
  set hideXs(val) {
    this._cacheInput("showXsPrint", negativeOf(val));
  }
}