feat(expansion): allow expansion indicator positioning.

src/demo-app/expansion/expansion-demo.html

@@ -43,6 +43,11 @@ <h1>matAccordion</h1>
     <mat-radio-button value="default">Default</mat-radio-button>
     <mat-radio-button value="flat">Flat</mat-radio-button>
   </mat-radio-group>
+  <p>Toggle Position</p>
+  <mat-radio-group [(ngModel)]="togglePosition">
+    <mat-radio-button value="before">Before</mat-radio-button>
+    <mat-radio-button value="after">After</mat-radio-button>
+  </mat-radio-group>
   <p>Accordion Actions <sup>('Multi Expansion' mode only)</sup></p>
   <div>
     <button mat-button (click)="accordion.openAll()" [disabled]="!multi">Expand All</button>
@@ -55,8 +60,8 @@ <h1>matAccordion</h1>
   </div>
 </div>
 <br>
-<mat-accordion [displayMode]="displayMode" [multi]="multi"
-              class="demo-expansion-width">
+<mat-accordion [displayMode]="displayMode" [multi]="multi" [togglePosition]="togglePosition"
+               class="demo-expansion-width">
   <mat-expansion-panel #panel1  [hideToggle]="hideToggle">
     <mat-expansion-panel-header>Section 1</mat-expansion-panel-header>
     <p>This is the content text that makes sense here.</p>
@@ -75,7 +80,7 @@ <h1>matAccordion</h1>
   </mat-expansion-panel>
 </mat-accordion>
 
-<h1>cdkAccordion</h1>
+<h1>CdkAccordion</h1>
 <div>
   <p>Accordion Options</p>
   <div>
@@ -108,4 +113,3 @@ <h1>cdkAccordion</h1>
     <p *ngIf="item3.expanded">I only show if item 3 is expanded</p>
   </cdk-accordion-item>
 </cdk-accordion>
-

src/demo-app/expansion/expansion-demo.ts

@@ -20,6 +20,7 @@ export class ExpansionDemo {
   @ViewChild(MatAccordion) accordion: MatAccordion;
 
   displayMode = 'default';
+  togglePosition = 'after';
   multi = false;
   hideToggle = false;
   disabled = false;

src/lib/expansion/_expansion-theme.scss

@@ -30,7 +30,7 @@
   }
 
   .mat-expansion-panel-header-description,
-  .mat-expansion-indicator::after {
+  .mat-expansion-indicator {
     color: mat-color($foreground, secondary-text);
   }
 

src/lib/expansion/accordion.spec.ts

@@ -5,7 +5,7 @@ import {BrowserAnimationsModule} from '@angular/platform-browser/animations';
 import {MatExpansionModule, MatAccordion} from './index';
 
 
-describe('CdkAccordion', () => {
+describe('MatAccordion', () => {
   beforeEach(async(() => {
     TestBed.configureTestingModule({
       imports: [
@@ -83,12 +83,39 @@ describe('CdkAccordion', () => {
     fixture.detectChanges();
     expect(panels[0].classes['mat-expanded']).toBeFalsy();
     expect(panels[1].classes['mat-expanded']).toBeFalsy();
+
+  });
+
+  it('should correctly apply the displayMode provided', () => {
+    const fixture = TestBed.createComponent(SetOfItems);
+    const firstPanel = fixture.debugElement.queryAll(By.css('.mat-expansion-panel'))[0];
+
+    fixture.componentInstance.firstPanelExpanded = true;
+    fixture.detectChanges();
+    expect(firstPanel.classes['mat-expansion-panel-spacing']).toBeTruthy();
+
+    fixture.componentInstance.displayMode = 'flat';
+    fixture.detectChanges();
+    expect(firstPanel.classes['mat-expansion-panel-spacing']).toBeFalsy();
+  });
+
+  it('should correctly apply the togglePosition provided', () => {
+    const fixture = TestBed.createComponent(SetOfItems);
+    fixture.detectChanges();
+    const firstPanelHeader =
+        fixture.debugElement.queryAll(By.css('.mat-expansion-indicator-container'))[0];
+
+    expect(firstPanelHeader.classes['mat-expansion-indicator-container-before']).toBeFalsy();
+
+    fixture.componentInstance.togglePosition = 'before';
+    fixture.detectChanges();
+    expect(firstPanelHeader.classes['mat-expansion-indicator-container-before']).toBeTruthy();
   });
 });
 
 
 @Component({template: `
-  <mat-accordion [multi]="multi">
+  <mat-accordion [multi]="multi" [displayMode]="displayMode" [togglePosition]="togglePosition">
     <mat-expansion-panel [expanded]="firstPanelExpanded">
       <mat-expansion-panel-header>Summary</mat-expansion-panel-header>
       <p>Content</p>
@@ -102,6 +129,8 @@ class SetOfItems {
   @ViewChild(MatAccordion) accordion: MatAccordion;
 
   multi: boolean = false;
+  displayMode = 'default';
+  togglePosition = 'after';
   firstPanelExpanded: boolean = false;
   secondPanelExpanded: boolean = false;
   secondPanelDisabled: boolean = false;

src/lib/expansion/accordion.ts

@@ -6,13 +6,18 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {Directive, Input} from '@angular/core';
+import {Directive, Input, SimpleChanges} from '@angular/core';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
 import {CdkAccordion} from '@angular/cdk/accordion';
+import {Subject} from 'rxjs';
 
 /** MatAccordion's display modes. */
 export type MatAccordionDisplayMode = 'default' | 'flat';
 
+
+ /** MatAccordion's toggle positions. */
+ export type MatAccordionTogglePosition = 'before' | 'after';
+
 /**
  * Directive for a Material Design Accordion.
  */
@@ -24,6 +29,9 @@ export type MatAccordionDisplayMode = 'default' | 'flat';
   }
 })
 export class MatAccordion extends CdkAccordion {
+  /** Stream that emits for changes in `@Input` properties. */
+  _inputChanges = new Subject<SimpleChanges>();
+
   /** Whether the expansion indicator should be hidden. */
   @Input()
   get hideToggle(): boolean { return this._hideToggle; }
@@ -39,4 +47,15 @@ export class MatAccordion extends CdkAccordion {
    *     elevation.
    */
   @Input() displayMode: MatAccordionDisplayMode = 'default';
+
+  /** The positioning of the expansion indicator. */
+  @Input() togglePosition: MatAccordionTogglePosition = 'after';
+
+  ngOnChanges(changes: SimpleChanges) {
+    this._inputChanges.next(changes);
+  }
+
+  ngOnDestroy() {
+    this._inputChanges.complete();
+  }
 }

src/lib/expansion/expansion-animations.ts

@@ -28,8 +28,8 @@ export const matExpansionAnimations: {
 } = {
   /** Animation that rotates the indicator arrow. */
   indicatorRotate: trigger('indicatorRotate', [
-    state('collapsed', style({transform: 'rotate(0deg)'})),
-    state('expanded', style({transform: 'rotate(180deg)'})),
+    state('collapsed', style({transform: 'rotate(45deg)'})),
+    state('expanded', style({transform: 'rotate(225deg)'})),
     transition('expanded <=> collapsed', animate(EXPANSION_PANEL_ANIMATION_TIMING)),
   ]),
 

src/lib/expansion/expansion-panel-header.html

@@ -3,5 +3,8 @@
   <ng-content select="mat-panel-description"></ng-content>
   <ng-content></ng-content>
 </span>
-<span [@indicatorRotate]="_getExpandedState()" *ngIf="_showToggle()"
-      class="mat-expansion-indicator"></span>
+<div class="mat-expansion-indicator-container"
+     [class.mat-expansion-indicator-container-before]="_placeToggleBefore()">
+     <span *ngIf="_isToggleVisible()" class="mat-expansion-indicator"
+           [@indicatorRotate]="_getExpandedState()"></span>
+</div>

src/lib/expansion/expansion-panel-header.scss

@@ -1,9 +1,8 @@
-
 .mat-expansion-panel-header {
   display: flex;
   flex-direction: row;
   align-items: center;
-  padding: 0 24px;
+  padding: 0 16px;
 
   &:focus,
   &:hover {
@@ -25,12 +24,13 @@
   flex: 1;
   flex-direction: row;
   overflow: hidden;
+  padding-left: 8px;
 }
 
 .mat-expansion-panel-header-title,
 .mat-expansion-panel-header-description {
   display: flex;
-  flex-grow: 1;
+  flex: 1;
   margin-right: 16px;
 
   [dir='rtl'] & {
@@ -40,19 +40,37 @@
 }
 
 .mat-expansion-panel-header-description {
-  flex-grow: 2;
+  flex: 2;
+}
+
+.mat-expansion-indicator-container {
+  // A margin is required to offset the entire expansion indicator against the space the arrow
+  // takes up.  It is calculated as sqrt(2 * border-width ^ 2) / 2.
+  margin-bottom: 1.41px;
+  padding: 0 8px 0 0;
+  width: 8px;
+  order: 1;
+
+  &.mat-expansion-indicator-container-before {
+    order: -1;
+    padding: 0 8px;
+  }
 }
 
-/**
- * Creates the expansion indicator arrow. Done using ::after rather than having
- * additional nodes in the template.
- */
-.mat-expansion-indicator::after {
+.mat-expansion-indicator {
   border-style: solid;
   border-width: 0 2px 2px 0;
-  content: '';
-  display: inline-block;
-  padding: 3px;
+  display: block;
+  height: 6px;
   transform: rotate(45deg);
-  vertical-align: middle;
+  // The transform origin is set by determining the center pointer of the arrow created. It is
+  // calculated as by calculating the length of the line between the top left corner of the div,
+  // and the centroid of the triangle created in the bottom right half of the div.  This centroid
+  // is calculated for both X and Y (as the indicator is a square) as 
+  // (indicator-width + indicator-height + 0) / 3
+  // The length between the resulting coordinates and the top left (0, 0) of the div are 
+  // calculated sqrt((centroids-x-coord ^ 2) + (centroids-y-coord ^ 2))
+  // This value is used to transform the origin on both the X and Y axes.
+  transform-origin: 5.65px 5.65px;
+  width: 6px;
 }

src/lib/expansion/expansion-panel-header.ts

@@ -16,13 +16,15 @@ import {
   ElementRef,
   Host,
   Input,
+  Optional,
   OnDestroy,
   ViewEncapsulation,
 } from '@angular/core';
 import {merge, Subscription} from 'rxjs';
 import {filter} from 'rxjs/operators';
 import {matExpansionAnimations} from './expansion-animations';
 import {MatExpansionPanel} from './expansion-panel';
+import {MatAccordion} from './accordion';
 
 
 /**
@@ -65,17 +67,24 @@ export class MatExpansionPanelHeader implements OnDestroy {
   private _parentChangeSubscription = Subscription.EMPTY;
 
   constructor(
+    @Optional() accordion: MatAccordion,
     @Host() public panel: MatExpansionPanel,
     private _element: ElementRef,
     private _focusMonitor: FocusMonitor,
     private _changeDetectorRef: ChangeDetectorRef) {
 
+    let changeStreams = [panel._inputChanges];
+    if (accordion) {
+      changeStreams.push(accordion._inputChanges);
+    }
+
     // Since the toggle state depends on an @Input on the panel, we
-    // need to  subscribe and trigger change detection manually.
+    // need to subscribe and trigger change detection manually.
     this._parentChangeSubscription = merge(
       panel.opened,
       panel.closed,
-      panel._inputChanges.pipe(filter(changes => !!(changes.hideToggle || changes.disabled)))
+      merge(...changeStreams).pipe(
+        filter(changes => !!(changes.hideToggle || changes.disabled || changes.togglePosition)))
     )
     .subscribe(() => this._changeDetectorRef.markForCheck());
 
@@ -109,10 +118,15 @@ export class MatExpansionPanelHeader implements OnDestroy {
   }
 
   /** Gets whether the expand indicator should be shown. */
-  _showToggle(): boolean {
+  _isToggleVisible(): boolean {
     return !this.panel.hideToggle && !this.panel.disabled;
   }
 
+  /** Whether the expand indicator should be shown before the header content */
+  _placeToggleBefore(): boolean {
+    return this.panel.togglePosition === 'before';
+  }
+
   /** Handle keydown event calling to toggle() if appropriate. */
   _keydown(event: KeyboardEvent) {
     switch (event.keyCode) {

src/lib/expansion/expansion-panel.ts

@@ -28,9 +28,9 @@ import {
 } from '@angular/core';
 import {Subject} from 'rxjs';
 import {filter, startWith, take} from 'rxjs/operators';
-import {MatAccordion} from './accordion';
-import {matExpansionAnimations} from './expansion-animations';
+import {MatAccordion, MatAccordionTogglePosition} from './accordion';
 import {MatExpansionPanelContent} from './expansion-panel-content';
+import {matExpansionAnimations} from './expansion-animations';
 
 
 /** MatExpansionPanel's states. */
@@ -72,6 +72,16 @@ export class MatExpansionPanel extends CdkAccordionItem
   }
   private _hideToggle = false;
 
+  /** The positioning of the expansion indicator. */
+  @Input()
+  get togglePosition(): MatAccordionTogglePosition {
+    return this.accordion ? this.accordion.togglePosition : this._togglePosition;
+  }
+  set togglePosition(position: MatAccordionTogglePosition) {
+    this._togglePosition = position;
+  }
+  private _togglePosition: MatAccordionTogglePosition = 'after';
+
   /** Stream that emits for changes in `@Input` properties. */
   readonly _inputChanges = new Subject<SimpleChanges>();
 

src/lib/expansion/expansion.md

@@ -15,7 +15,8 @@ header to align with Material Design specifications.
 
 By default, the expansion-panel header includes a toggle icon at the end of the
 header to indicate the expansion state. This icon can be hidden via the
-`hideToggle` property.
+`hideToggle` property.  The icon's position can also be configured with the `togglePosition`
+property.
 
 ```html
 <mat-expansion-panel>