feat(material-experimental/mdc-tabs): add option to fit ink bar to content

src/dev-app/mdc-tabs/mdc-tabs-demo.html

@@ -91,6 +91,23 @@ <h2>Template labels</h2>
     </mat-tab>
   </mat-tab-group>
 
+  <h2>Ink bar fit to content</h2>
+  <button (click)="fitInkBarToContent = !fitInkBarToContent"> Toggle Fit To Content </button>
+  <mat-tab-group [fitInkBarToContent]="fitInkBarToContent">
+    <mat-tab label="First">Content 1</mat-tab>
+    <mat-tab label="Second">Content 2</mat-tab>
+    <mat-tab label="Third">Content 3</mat-tab>
+    <mat-tab label="Fourth" disabled>Content 4</mat-tab>
+  </mat-tab-group>
+
+  <h2>Ink bar fit to content</h2>
+  <nav mat-tab-nav-bar [fitInkBarToContent]="fitInkBarToContent">
+    <a mat-tab-link *ngFor="let link of links"
+       (click)="activeLink = link"
+       [active]="activeLink == link">{{link}}</a>
+    <a mat-tab-link disabled>Disabled Link</a>
+  </nav>
+
   <h2>Lazy tabs</h2>
   <mat-tab-group>
     <mat-tab label="One">

src/dev-app/mdc-tabs/mdc-tabs-demo.ts

@@ -15,6 +15,7 @@ import {Component} from '@angular/core';
   styleUrls: ['mdc-tabs-demo.css'],
 })
 export class MdcTabsDemo {
+  fitInkBarToContent = true;
   links = ['First', 'Second', 'Third'];
   lotsOfTabs = new Array(30).fill(0).map((_, index) => `Tab ${index}`);
   activeLink = this.links[0];

src/material-experimental/mdc-tabs/ink-bar.ts

@@ -8,9 +8,9 @@
 
 import {ElementRef, QueryList} from '@angular/core';
 import {
-  MDCTabIndicatorFoundation,
   MDCSlidingTabIndicatorFoundation,
-  MDCTabIndicatorAdapter
+  MDCTabIndicatorAdapter,
+  MDCTabIndicatorFoundation
 } from '@material/tab-indicator';
 
 /**
@@ -23,7 +23,7 @@ export interface MatInkBarItem {
 }
 
 /**
- * Abstraction around the MDC tab indicator that manages the ink bar of a tab header.
+ * Abstraction around the MDC tab indicator that acts as the tab header's ink bar.
  * @docs-private
  */
 export class MatInkBar {
@@ -50,49 +50,47 @@ export class MatInkBar {
       const clientRect = currentItem ?
           currentItem._foundation.computeContentClientRect() : undefined;
 
-      // The MDC indicator won't animate unless we give it the `ClientRect` of the previous item.
+      // The ink bar won't animate unless we give it the `ClientRect` of the previous item.
       correspondingItem._foundation.activate(clientRect);
       this._currentItem = correspondingItem;
     }
   }
 }
 
 /**
- * Implementation of MDC's sliding tab indicator foundation.
+ * Implementation of MDC's sliding tab indicator (ink bar) foundation.
  * @docs-private
  */
 export class MatInkBarFoundation {
   private _destroyed: boolean;
   private _foundation: MDCTabIndicatorFoundation;
-  private _element: HTMLElement;
-  private _indicator: HTMLElement;
-  private _indicatorContent: HTMLElement;
+  private _inkBarElement: HTMLElement;
+  private _inkBarContentElement: HTMLElement;
+  private _fitToContent = false;
   private _adapter: MDCTabIndicatorAdapter = {
     addClass: className => {
       if (!this._destroyed) {
-        this._element.classList.add(className);
+        this._hostElement.classList.add(className);
       }
     },
     removeClass: className => {
       if (!this._destroyed) {
-        this._element.classList.remove(className);
+        this._hostElement.classList.remove(className);
       }
     },
     setContentStyleProperty: (propName, value) => {
-      this._indicatorContent.style.setProperty(propName, value);
+      this._inkBarContentElement.style.setProperty(propName, value);
     },
     computeContentClientRect: () => {
       // `getBoundingClientRect` isn't available on the server.
-      return this._destroyed || !this._indicatorContent.getBoundingClientRect ? {
+      return this._destroyed || !this._inkBarContentElement.getBoundingClientRect ? {
         width: 0, height: 0, top: 0, left: 0, right: 0, bottom: 0
-      } : this._indicatorContent.getBoundingClientRect();
+      } : this._inkBarContentElement.getBoundingClientRect();
     }
   };
 
-  constructor(elementRef: ElementRef<HTMLElement>, document: Document) {
-    this._element = elementRef.nativeElement;
+  constructor(private _hostElement: HTMLElement, private _document: Document) {
     this._foundation = new MDCSlidingTabIndicatorFoundation(this._adapter);
-    this._createIndicator(document);
   }
 
   /** Aligns the ink bar to the current item. */
@@ -105,39 +103,78 @@ export class MatInkBarFoundation {
     this._foundation.deactivate();
   }
 
-  /** Gets the ClientRect of the indicator. */
+  /** Gets the ClientRect of the ink bar. */
   computeContentClientRect() {
     return this._foundation.computeContentClientRect();
   }
 
   /** Initializes the foundation. */
   init() {
+    this._createInkBarElement();
     this._foundation.init();
   }
 
   /** Destroys the foundation. */
   destroy() {
-    const indicator = this._indicator;
-
-    if (indicator.parentNode) {
-      indicator.parentNode.removeChild(indicator);
+    if (this._inkBarElement.parentNode) {
+      this._inkBarElement.parentNode.removeChild(this._inkBarElement);
     }
 
-    this._element = this._indicator = this._indicatorContent = null!;
+    this._hostElement = this._inkBarElement = this._inkBarContentElement = null!;
     this._foundation.destroy();
     this._destroyed = true;
   }
 
-  private _createIndicator(document: Document) {
-    if (!this._indicator) {
-      const indicator = this._indicator = document.createElement('span');
-      const content = this._indicatorContent = document.createElement('span');
+  /**
+   * Sets whether the ink bar should be appended to the content, which will cause the ink bar
+   * to match the width of the content rather than the tab host element.
+   */
+  setFitToContent(fitToContent: boolean) {
+    if (this._fitToContent !== fitToContent) {
+      this._fitToContent = fitToContent;
+      if (this._inkBarElement) {
+        this._appendInkBarElement();
+      }
+    }
+  }
+
+
+  /**
+   * Gets whether the ink bar should be appended to the content, which will cause the ink bar
+   * to match the width of the content rather than the tab host element.
+   */
+  getFitToContent(): boolean { return this._fitToContent; }
+
+  /** Creates and appends the ink bar element. */
+  private _createInkBarElement() {
+    this._inkBarElement = this._document.createElement('span');
+    this._inkBarContentElement = this._document.createElement('span');
 
-      indicator.className = 'mdc-tab-indicator';
-      content.className = 'mdc-tab-indicator__content mdc-tab-indicator__content--underline';
+    this._inkBarElement.className = 'mdc-tab-indicator';
+    this._inkBarContentElement.className = 'mdc-tab-indicator__content' +
+        ' mdc-tab-indicator__content--underline';
 
-      indicator.appendChild(content);
-      this._element.appendChild(indicator);
+    this._inkBarElement.appendChild(this._inkBarContentElement);
+    this._appendInkBarElement();
+  }
+
+  /**
+   * Appends the ink bar to the tab host element or content, depending on whether
+   * the ink bar should fit to content.
+   */
+  private _appendInkBarElement() {
+    if (!this._inkBarElement) {
+      throw Error('Ink bar element has not been created and cannot be appended');
+    }
+
+    const parentElement = this._fitToContent ?
+        this._hostElement.querySelector('.mdc-tab__content') :
+        this._hostElement;
+
+    if (!parentElement) {
+      throw Error('Missing element to host the ink bar');
     }
+
+    parentElement.appendChild(this._inkBarElement);
   }
 }

src/material-experimental/mdc-tabs/tab-group.html

@@ -20,6 +20,7 @@
        [attr.aria-labelledby]="(!tab.ariaLabel && tab.ariaLabelledby) ? tab.ariaLabelledby : null"
        [class.mdc-tab--active]="selectedIndex == i"
        [disabled]="tab.disabled"
+       [fitInkBarToContent]="fitInkBarToContent"
        (click)="_handleClick(tab, tabHeader, i)">
     <span class="mdc-tab__ripple"></span>
 

src/material-experimental/mdc-tabs/tab-group.spec.ts

@@ -677,6 +677,47 @@ describe('nested MatTabGroup with enabled animations', () => {
 });
 
 
+describe('MatTabGroup with ink bar fit to content', () => {
+  let fixture: ComponentFixture<TabGroupWithInkBarFitToContent>;
+
+  beforeEach(fakeAsync(() => {
+    TestBed.configureTestingModule({
+      imports: [MatTabsModule, BrowserAnimationsModule],
+      declarations: [TabGroupWithInkBarFitToContent]
+    });
+
+    TestBed.compileComponents();
+  }));
+
+  beforeEach(() => {
+    fixture = TestBed.createComponent(TabGroupWithInkBarFitToContent);
+    fixture.detectChanges();
+  });
+
+  it('should properly nest the ink bar when fit to content', () => {
+    const tabElement = fixture.nativeElement.querySelector('.mdc-tab');
+    const contentElement = tabElement.querySelector('.mdc-tab__content');
+    const indicatorElement = tabElement.querySelector('.mdc-tab-indicator');
+    expect(indicatorElement.parentElement).toBe(contentElement);
+  });
+
+  it('should be able to move the ink bar between content and full', () => {
+    fixture.componentInstance.fitInkBarToContent = false;
+    fixture.detectChanges();
+
+    const tabElement = fixture.nativeElement.querySelector('.mdc-tab');
+    const indicatorElement = tabElement.querySelector('.mdc-tab-indicator');
+    expect(indicatorElement.parentElement).toBe(tabElement);
+
+    fixture.componentInstance.fitInkBarToContent = true;
+    fixture.detectChanges();
+
+    const contentElement = tabElement.querySelector('.mdc-tab__content');
+    expect(indicatorElement.parentElement).toBe(contentElement);
+  });
+});
+
+
 @Component({
   template: `
     <mat-tab-group class="tab-group"
@@ -928,3 +969,16 @@ class TabsWithCustomAnimationDuration {}
 class TabGroupWithIndirectDescendantTabs {
   @ViewChild(MatTabGroup) tabGroup: MatTabGroup;
 }
+
+
+@Component({
+  template: `
+    <mat-tab-group [fitInkBarToContent]="fitInkBarToContent">
+      <mat-tab label="One">Tab one content</mat-tab>
+      <mat-tab label="Two">Tab two content</mat-tab>
+    </mat-tab-group>
+  `,
+})
+class TabGroupWithInkBarFitToContent {
+  fitInkBarToContent = true;
+}

src/material-experimental/mdc-tabs/tab-group.ts

@@ -8,25 +8,27 @@
 
 import {
   ChangeDetectionStrategy,
+  ChangeDetectorRef,
   Component,
   ContentChildren,
   ElementRef,
+  Inject,
+  Input,
+  Optional,
   QueryList,
   ViewChild,
   ViewEncapsulation,
-  ChangeDetectorRef,
-  Inject,
-  Optional,
 } from '@angular/core';
 import {
   _MatTabGroupBase,
+  MAT_TAB_GROUP,
   MAT_TABS_CONFIG,
   MatTabsConfig,
-  MAT_TAB_GROUP,
 } from '@angular/material/tabs';
 import {ANIMATION_MODULE_TYPE} from '@angular/platform-browser/animations';
 import {MatTab} from './tab';
 import {MatTabHeader} from './tab-header';
+import {coerceBooleanProperty} from '@angular/cdk/coercion';
 
 /**
  * Material design tab-group component. Supports basic tab pairs (label + content) and includes
@@ -57,6 +59,12 @@ export class MatTabGroup extends _MatTabGroupBase {
   @ViewChild('tabBodyWrapper') _tabBodyWrapper: ElementRef;
   @ViewChild('tabHeader') _tabHeader: MatTabHeader;
 
+  /** Whether the ink bar should fit its width to the size of the tab label content. */
+  @Input()
+  get fitInkBarToContent(): boolean { return this._fitInkBarToContent; }
+  set fitInkBarToContent(v: boolean) { this._fitInkBarToContent = coerceBooleanProperty(v); }
+  private _fitInkBarToContent = false;
+
   constructor(elementRef: ElementRef,
               changeDetectorRef: ChangeDetectorRef,
               @Inject(MAT_TABS_CONFIG) @Optional() defaultConfig?: MatTabsConfig,

src/material-experimental/mdc-tabs/tab-label-wrapper.ts

@@ -6,10 +6,11 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {Directive, ElementRef, Inject, OnDestroy} from '@angular/core';
+import {Directive, ElementRef, Inject, Input, OnDestroy, OnInit} from '@angular/core';
 import {DOCUMENT} from '@angular/common';
 import {MatTabLabelWrapper as BaseMatTabLabelWrapper} from '@angular/material/tabs';
 import {MatInkBarFoundation, MatInkBarItem} from './ink-bar';
+import {coerceBooleanProperty} from '@angular/cdk/coercion';
 
 /**
  * Used in the `mat-tab-group` view to display tab labels.
@@ -23,12 +24,24 @@ import {MatInkBarFoundation, MatInkBarItem} from './ink-bar';
     '[attr.aria-disabled]': '!!disabled',
   }
 })
-export class MatTabLabelWrapper extends BaseMatTabLabelWrapper implements MatInkBarItem, OnDestroy {
+export class MatTabLabelWrapper extends BaseMatTabLabelWrapper
+    implements MatInkBarItem, OnInit, OnDestroy {
+  private _document: Document;
+
   _foundation: MatInkBarFoundation;
 
+  /** Whether the ink bar should fit its width to the size of the tab label content. */
+  @Input()
+  get fitInkBarToContent(): boolean { return this._foundation.getFitToContent(); }
+  set fitInkBarToContent(v: boolean) { this._foundation.setFitToContent(coerceBooleanProperty(v)); }
+
   constructor(public elementRef: ElementRef, @Inject(DOCUMENT) _document: any) {
     super(elementRef);
-    this._foundation = new MatInkBarFoundation(elementRef, _document);
+    this._document = _document;
+    this._foundation = new MatInkBarFoundation(this.elementRef.nativeElement, this._document);
+  }
+
+  ngOnInit() {
     this._foundation.init();
   }