feat(expansion): add animation events for expansion panels (#12412)

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

@@ -1,6 +1,8 @@
 <h1>Single Expansion Panel</h1>
 
-<mat-expansion-panel class="demo-expansion-width" #myPanel>
+<mat-expansion-panel class="demo-expansion-width" #myPanel
+                     (afterExpand)="addEvent('afterExpand')"
+                     (afterCollapse)="addEvent('afterCollapse')">
   <mat-expansion-panel-header [expandedHeight]="expandedHeight" [collapsedHeight]="collapsedHeight">
     <mat-panel-description>This is a panel description.</mat-panel-description>
     <mat-panel-title>Panel Title</mat-panel-title>
@@ -29,6 +31,11 @@ <h1>Single Expansion Panel</h1>
 </mat-form-field>
 <br>
 
+<p>Expansion Panel Animation Events</p>
+<code class="demo-expansion-code">
+  <pre *ngFor="let event of events">{{event}}</pre>
+</code>
+
 <h1>matAccordion</h1>
 <div>
   <p>Accordion Options</p>
@@ -56,7 +63,7 @@ <h1>matAccordion</h1>
 </div>
 <br>
 <mat-accordion [displayMode]="displayMode" [multi]="multi"
-              class="demo-expansion-width">
+               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>

src/demo-app/expansion/expansion-demo.scss

@@ -2,3 +2,16 @@
   width: 600px;
   display: block;
 }
+
+.demo-expansion-code {
+  background: #d3d3d3;
+  display: block;
+  height: 10em;
+  overflow: auto;
+  padding: 0 5px;
+  width: 400px;
+
+  pre {
+    margin: 0.25em 0;
+  }
+}

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

@@ -26,4 +26,9 @@ export class ExpansionDemo {
   showPanel3 = true;
   expandedHeight: string;
   collapsedHeight: string;
+  events: string[] = [];
+
+  addEvent(eventName: string) {
+    this.events.push(`${eventName} - ${new Date().toISOString()}`);
+  }
 }

src/lib/expansion/expansion-panel.ts

@@ -18,10 +18,12 @@ import {
   Component,
   ContentChild,
   Directive,
+  EventEmitter,
   Input,
   OnChanges,
   OnDestroy,
   Optional,
+  Output,
   SimpleChanges,
   SkipSelf,
   ViewContainerRef,
@@ -69,7 +71,7 @@ let uniqueId = 0;
   }
 })
 export class MatExpansionPanel extends CdkAccordionItem
-    implements AfterContentInit, OnChanges, OnDestroy {
+  implements AfterContentInit, OnChanges, OnDestroy {
   /** Whether the toggle indicator should be hidden. */
   @Input()
   get hideToggle(): boolean { return this._hideToggle; }
@@ -78,6 +80,12 @@ export class MatExpansionPanel extends CdkAccordionItem
   }
   private _hideToggle = false;
 
+  /** An event emitted after the body's expansion animation happens. */
+  @Output() afterExpand = new EventEmitter<void>();
+
+  /** An event emitted after the body's collapse animation happens. */
+  @Output() afterCollapse = new EventEmitter<void>();
+
   /** Stream that emits for changes in `@Input` properties. */
   readonly _inputChanges = new Subject<SimpleChanges>();
 
@@ -147,17 +155,25 @@ export class MatExpansionPanel extends CdkAccordionItem
   _bodyAnimation(event: AnimationEvent) {
     const classList = event.element.classList;
     const cssClass = 'mat-expanded';
-    const {phaseName, toState} = event;
+    const {phaseName, toState, fromState} = event;
 
     // Toggle the body's `overflow: hidden` class when closing starts or when expansion ends in
     // order to prevent the cases where switching too early would cause the animation to jump.
     // Note that we do it directly on the DOM element to avoid the slight delay that comes
     // with doing it via change detection.
     if (phaseName === 'done' && toState === 'expanded') {
       classList.add(cssClass);
-    } else if (phaseName === 'start' && toState === 'collapsed') {
+    }
+    if (phaseName === 'start' && toState === 'collapsed') {
       classList.remove(cssClass);
     }
+
+    if (phaseName === 'done' && toState === 'expanded' && fromState !== 'void') {
+      this.afterExpand.emit();
+    }
+    if (phaseName === 'done' && toState === 'collapsed' && fromState !== 'void') {
+      this.afterCollapse.emit();
+    }
   }
 }
 

src/lib/expansion/expansion.spec.ts

@@ -11,8 +11,8 @@ describe('MatExpansionPanel', () => {
   beforeEach(async(() => {
     TestBed.configureTestingModule({
       imports: [
+        MatExpansionModule,
         NoopAnimationsModule,
-        MatExpansionModule
       ],
       declarations: [
         PanelWithContent,
@@ -44,8 +44,9 @@ describe('MatExpansionPanel', () => {
   }));
 
   it('should be able to render panel content lazily', fakeAsync(() => {
-    let fixture = TestBed.createComponent(LazyPanelWithContent);
-    let content = fixture.debugElement.query(By.css('.mat-expansion-panel-content')).nativeElement;
+    const fixture = TestBed.createComponent(LazyPanelWithContent);
+    const content = fixture.debugElement.query(
+      By.css('.mat-expansion-panel-content')).nativeElement;
     fixture.detectChanges();
 
     expect(content.textContent.trim()).toBe('', 'Expected content element to be empty.');
@@ -58,8 +59,9 @@ describe('MatExpansionPanel', () => {
   }));
 
   it('should render the content for a lazy-loaded panel that is opened on init', fakeAsync(() => {
-    let fixture = TestBed.createComponent(LazyPanelOpenOnLoad);
-    let content = fixture.debugElement.query(By.css('.mat-expansion-panel-content')).nativeElement;
+    const fixture = TestBed.createComponent(LazyPanelOpenOnLoad);
+    const content = fixture.debugElement.query(
+      By.css('.mat-expansion-panel-content')).nativeElement;
     fixture.detectChanges();
 
     expect(content.textContent.trim())
@@ -161,10 +163,10 @@ describe('MatExpansionPanel', () => {
   }));
 
   it('should not override the panel margin if it is not inside an accordion', fakeAsync(() => {
-    let fixture = TestBed.createComponent(PanelWithCustomMargin);
+    const fixture = TestBed.createComponent(PanelWithCustomMargin);
     fixture.detectChanges();
 
-    let panel = fixture.debugElement.query(By.css('mat-expansion-panel'));
+    const panel = fixture.debugElement.query(By.css('mat-expansion-panel'));
     let styles = getComputedStyle(panel.nativeElement);
 
     expect(panel.componentInstance._hasSpacing()).toBe(false);
@@ -221,7 +223,7 @@ describe('MatExpansionPanel', () => {
     }));
 
   it('should make sure accordion item runs ngOnDestroy when expansion panel is destroyed', () => {
-    let fixture = TestBed.createComponent(PanelWithContentInNgIf);
+    const fixture = TestBed.createComponent(PanelWithContentInNgIf);
     fixture.detectChanges();
     let destroyedOk = false;
     fixture.componentInstance.panel.destroyed.subscribe(() => destroyedOk = true);
@@ -264,6 +266,27 @@ describe('MatExpansionPanel', () => {
         'Expected class to be added after the animation has finished');
   }));
 
+  it('should emit events for body expanding and collapsing animations', fakeAsync(() => {
+    const fixture = TestBed.createComponent(PanelWithContent);
+    fixture.detectChanges();
+    let afterExpand = 0;
+    let afterCollapse = 0;
+    fixture.componentInstance.panel.afterExpand.subscribe(() => afterExpand++);
+    fixture.componentInstance.panel.afterCollapse.subscribe(() => afterCollapse++);
+
+    fixture.componentInstance.expanded = true;
+    fixture.detectChanges();
+    flush();
+    expect(afterExpand).toBe(1);
+    expect(afterCollapse).toBe(0);
+
+    fixture.componentInstance.expanded = false;
+    fixture.detectChanges();
+    flush();
+    expect(afterExpand).toBe(1);
+    expect(afterCollapse).toBe(1);
+  }));
+
   describe('disabled state', () => {
     let fixture: ComponentFixture<PanelWithContent>;
     let panel: HTMLElement;
@@ -373,7 +396,7 @@ class PanelWithContentInNgIf {
   </mat-expansion-panel>`
 })
 class PanelWithCustomMargin {
-  expanded: boolean = false;
+  expanded = false;
 }
 
 @Component({