fix(tabs): observing tab header label changes to recalculate width

- Uses observe-changes directive that emit an event when the mutation observer notifies a change

fixes angular#2155

src/lib/core/core.ts

@@ -1,6 +1,7 @@
 import {NgModule, ModuleWithProviders} from '@angular/core';
 import {MdLineModule} from './line/line';
 import {RtlModule} from './rtl/dir';
+import {ObserveContentModule} from './observe-content/observe-content';
 import {MdRippleModule} from './ripple/ripple';
 import {PortalModule} from './portal/portal-directives';
 import {OverlayModule} from './overlay/overlay-directives';
@@ -11,6 +12,9 @@ import {OVERLAY_PROVIDERS} from './overlay/overlay';
 // RTL
 export {Dir, LayoutDirection, RtlModule} from './rtl/dir';
 
+// Mutation Observer
+export {ObserveContentModule, ObserveContent} from './observe-content/observe-content';
+
 // Portals
 export {
   Portal,
@@ -99,8 +103,10 @@ export {NoConflictStyleCompatibilityMode} from './compatibility/no-conflict-mode
 
 
 @NgModule({
-  imports: [MdLineModule, RtlModule, MdRippleModule, PortalModule, OverlayModule, A11yModule],
-  exports: [MdLineModule, RtlModule, MdRippleModule, PortalModule, OverlayModule, A11yModule],
+  imports: [MdLineModule, RtlModule, ObserveContentModule,
+            MdRippleModule, PortalModule, OverlayModule, A11yModule],
+  exports: [MdLineModule, RtlModule, ObserveContentModule,
+            MdRippleModule, PortalModule, OverlayModule, A11yModule],
 })
 export class MdCoreModule {
   static forRoot(): ModuleWithProviders {

src/lib/core/observe-content/observe-content.spec.ts

@@ -0,0 +1,65 @@
+import {Component} from '@angular/core';
+import {async, TestBed} from '@angular/core/testing';
+import {ObserveContentModule} from './observe-content';
+
+// TODO(elad): `ProxyZone` doesn't seem to capture the events raised by `MutationObserver` and needs to be investigated
+
+describe('Observe content', () => {
+  beforeEach(async(() => {
+    TestBed.configureTestingModule({
+      imports: [ObserveContentModule],
+      declarations: [ComponentWithTextContent, ComponentWithChildTextContent],
+    });
+
+    TestBed.compileComponents();
+  }));
+
+  describe('text content change', () => {
+    it('should call the registered for changes function', done => {
+      let fixture = TestBed.createComponent(ComponentWithTextContent);
+      fixture.detectChanges();
+
+      // If the hint label is empty, expect no label.
+      const spy = spyOn(fixture.componentInstance, 'doSomething').and.callFake(() => {
+        expect(spy.calls.any()).toBe(true);
+        done();
+      });
+
+      expect(spy.calls.any()).toBe(false);
+
+      fixture.componentInstance.text = 'text';
+      fixture.detectChanges();
+    });
+  });
+
+  describe('child text content change', () => {
+    it('should call the registered for changes function', done => {
+      let fixture = TestBed.createComponent(ComponentWithChildTextContent);
+      fixture.detectChanges();
+
+      // If the hint label is empty, expect no label.
+      const spy = spyOn(fixture.componentInstance, 'doSomething').and.callFake(() => {
+        expect(spy.calls.any()).toBe(true);
+        done();
+      });
+
+      expect(spy.calls.any()).toBe(false);
+
+      fixture.componentInstance.text = 'text';
+      fixture.detectChanges();
+    });
+  });
+});
+
+
+@Component({ template: `<div (cdk-observe-content)="doSomething()">{{text}}</div>` })
+class ComponentWithTextContent {
+  text = '';
+  doSomething() {}
+}
+
+@Component({ template: `<div (cdk-observe-content)="doSomething()"><div>{{text}}<div></div>` })
+class ComponentWithChildTextContent {
+  text = '';
+  doSomething() {}
+}

src/lib/core/observe-content/observe-content.ts

@@ -0,0 +1,48 @@
+import {
+  Directive,
+  ElementRef,
+  NgModule,
+  ModuleWithProviders,
+  Output,
+  EventEmitter,
+  OnDestroy,
+  AfterContentInit
+} from '@angular/core';
+
+@Directive({
+  selector: '[cdk-observe-content]'
+})
+export class ObserveContent implements AfterContentInit, OnDestroy {
+  private _observer: MutationObserver;
+
+  @Output('cdk-observe-content') event = new EventEmitter<void>();
+
+  constructor(private _elementRef: ElementRef) {}
+
+  ngAfterContentInit() {
+    this._observer = new MutationObserver(mutations => mutations.forEach(() => this.event.emit()));
+
+    this._observer.observe(this._elementRef.nativeElement, {
+      characterData: true,
+      childList: true,
+      subtree: true
+    });
+  }
+
+  ngOnDestroy() {
+    this._observer.disconnect();
+  }
+}
+
+@NgModule({
+  exports: [ObserveContent],
+  declarations: [ObserveContent]
+})
+export class ObserveContentModule {
+  static forRoot(): ModuleWithProviders {
+    return {
+      ngModule: ObserveContentModule,
+      providers: []
+    };
+  }
+}

src/lib/module.ts

@@ -3,6 +3,7 @@ import {NgModule, ModuleWithProviders} from '@angular/core';
 import {
   MdRippleModule,
   RtlModule,
+  ObserveContentModule,
   PortalModule,
   OverlayModule,
   A11yModule,
@@ -67,6 +68,7 @@ const MATERIAL_MODULES = [
   PlatformModule,
   ProjectionModule,
   DefaultStyleCompatibilityModeModule,
+  ObserveContentModule
 ];
 
 @NgModule({
@@ -89,6 +91,7 @@ const MATERIAL_MODULES = [
     PortalModule.forRoot(),
     ProjectionModule.forRoot(),
     RtlModule.forRoot(),
+    ObserveContentModule.forRoot(),
 
     // These modules include providers.
     A11yModule.forRoot(),

src/lib/tabs/tab-group.ts

@@ -23,6 +23,7 @@ import {MdInkBar} from './ink-bar';
 import {Observable} from 'rxjs/Observable';
 import 'rxjs/add/operator/map';
 import {MdRippleModule} from '../core/ripple/ripple';
+import {ObserveContentModule} from '../core/observe-content/observe-content';
 import {MdTab} from './tab';
 import {MdTabBody} from './tab-body';
 import {ViewportRuler} from '../core/overlay/position/viewport-ruler';
@@ -188,7 +189,7 @@ export class MdTabGroup {
 }
 
 @NgModule({
-  imports: [CommonModule, PortalModule, MdRippleModule],
+  imports: [CommonModule, PortalModule, MdRippleModule, ObserveContentModule],
   // Don't export all components because some are only to be used internally.
   exports: [MdTabGroup, MdTabLabel, MdTab, MdTabNavBar, MdTabLink, MdTabLinkRipple],
   declarations: [MdTabGroup, MdTabLabel, MdTab, MdInkBar, MdTabLabelWrapper,

src/lib/tabs/tab-header.html

@@ -8,7 +8,7 @@
 
 <div class="md-tab-label-container" #tabListContainer
      (keydown)="_handleKeydown($event)">
-  <div class="md-tab-list" #tabList role="tablist">
+  <div class="md-tab-list" #tabList role="tablist" (cdk-observe-content)="_updatePagination()">
     <ng-content></ng-content>
     <md-ink-bar></md-ink-bar>
   </div>

src/lib/tabs/tab-header.ts

@@ -101,9 +101,7 @@ export class MdTabHeader {
   ngAfterContentChecked(): void {
     // If the number of tab labels have changed, check if scrolling should be enabled
     if (this._tabLabelCount != this._labelWrappers.length) {
-      this._checkPaginationEnabled();
-      this._checkScrollingControls();
-      this._updateTabScrollPosition();
+      this._updatePagination();
       this._tabLabelCount = this._labelWrappers.length;
     }
 
@@ -150,6 +148,16 @@ export class MdTabHeader {
     }
   }
 
+  /**
+   * Updating the view whether pagination should be enabled or not
+   * @private
+   */
+  _updatePagination() {
+    this._checkPaginationEnabled();
+    this._checkScrollingControls();
+    this._updateTabScrollPosition();
+  }
+
   /** When the focus index is set, we must manually send focus to the correct label */
   set focusIndex(value: number) {
     if (!this._isValidIndex(value) || this._focusIndex == value) { return; }