feat(tabs): add input to opt out of pagination

Currently the tabs pagination works automatically by measuring the size of the tab header to figure out whether to show pagination. This measuring can be expensive because it triggers a page layout and might not necessarily be required if the page won't have enough tabs to paginate through.

These changes add an input and an option to the injection token to allow consumers to opt out of the pagination, if they know that they won't need it.

Fixes #17317.

Author: crisbeto

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

@@ -523,6 +523,40 @@ describe('MatTabHeader', () => {
 
     });
 
+    describe('disabling pagination', () => {
+      it('should not show the pagination controls if pagination is disabled', () => {
+        fixture = TestBed.createComponent(SimpleTabHeaderApp);
+        appComponent = fixture.componentInstance;
+        appComponent.disablePagination = true;
+        fixture.detectChanges();
+        expect(appComponent.tabHeader._showPaginationControls).toBe(false);
+
+        // Add enough tabs that it will obviously exceed the width
+        appComponent.addTabsForScrolling();
+        fixture.detectChanges();
+
+        expect(appComponent.tabHeader._showPaginationControls).toBe(false);
+      });
+
+      it('should not change the scroll position if pagination is disabled', () => {
+        fixture = TestBed.createComponent(SimpleTabHeaderApp);
+        appComponent = fixture.componentInstance;
+        appComponent.disablePagination = true;
+        fixture.detectChanges();
+        appComponent.addTabsForScrolling();
+        fixture.detectChanges();
+        expect(appComponent.tabHeader.scrollDistance).toBe(0);
+
+        appComponent.tabHeader.focusIndex = appComponent.tabs.length - 1;
+        fixture.detectChanges();
+        expect(appComponent.tabHeader.scrollDistance).toBe(0);
+
+        appComponent.tabHeader.focusIndex = 0;
+        fixture.detectChanges();
+        expect(appComponent.tabHeader.scrollDistance).toBe(0);
+      });
+    });
+
     it('should re-align the ink bar when the direction changes', fakeAsync(() => {
       fixture = TestBed.createComponent(SimpleTabHeaderApp);
       fixture.detectChanges();
@@ -618,7 +652,8 @@ interface Tab {
   <div [dir]="dir">
     <mat-tab-header [selectedIndex]="selectedIndex" [disableRipple]="disableRipple"
                (indexFocused)="focusedIndex = $event"
-               (selectFocusedIndex)="selectedIndex = $event">
+               (selectFocusedIndex)="selectedIndex = $event"
+               [disablePagination]="disablePagination">
       <div matTabLabelWrapper class="label-content" style="min-width: 30px; width: 30px"
            *ngFor="let tab of tabs; let i = index"
            [disabled]="!!tab.disabled"
@@ -641,6 +676,7 @@ class SimpleTabHeaderApp {
   disabledTabIndex = 1;
   tabs: Tab[] = [{label: 'tab one'}, {label: 'tab one'}, {label: 'tab one'}, {label: 'tab one'}];
   dir: Direction = 'ltr';
+  disablePagination: boolean;
 
   @ViewChild(MatTabHeader, {static: true}) tabHeader: MatTabHeader;
 

src/material/tabs/paginated-tab-header.ts

@@ -19,6 +19,7 @@ import {
   OnDestroy,
   Directive,
   Inject,
+  Input,
 } from '@angular/core';
 import {Direction, Directionality} from '@angular/cdk/bidi';
 import {coerceNumberProperty} from '@angular/cdk/coercion';
@@ -116,6 +117,13 @@ export abstract class MatPaginatedTabHeader implements AfterContentChecked, Afte
   /** Stream that will stop the automated scrolling. */
   private _stopScrolling = new Subject<void>();
 
+  /**
+   * Whether pagination should be disabled. This can be used to avoid unnecessary
+   * layout recalculations if it's known that pagination won't be required.
+   */
+  @Input()
+  disablePagination: boolean = false;
+
   /** The index of the active tab. */
   get selectedIndex(): number { return this._selectedIndex; }
   set selectedIndex(value: number) {
@@ -364,6 +372,10 @@ export abstract class MatPaginatedTabHeader implements AfterContentChecked, Afte
 
   /** Performs the CSS transformation on the tab list that will cause the list to scroll. */
   _updateTabScrollPosition() {
+    if (this.disablePagination) {
+      return;
+    }
+
     const scrollDistance = this.scrollDistance;
     const platform = this._platform;
     const translateX = this._getLayoutDirection() === 'ltr' ? -scrollDistance : scrollDistance;
@@ -422,9 +434,15 @@ export abstract class MatPaginatedTabHeader implements AfterContentChecked, Afte
    * should be called sparingly.
    */
   _scrollToLabel(labelIndex: number) {
+    if (this.disablePagination) {
+      return;
+    }
+
     const selectedLabel = this._items ? this._items.toArray()[labelIndex] : null;
 
-    if (!selectedLabel) { return; }
+    if (!selectedLabel) {
+      return;
+    }
 
     // The view length is the visible width of the tab labels.
     const viewLength = this._tabListContainer.nativeElement.offsetWidth;
@@ -460,18 +478,22 @@ export abstract class MatPaginatedTabHeader implements AfterContentChecked, Afte
    * should be called sparingly.
    */
   _checkPaginationEnabled() {
-    const isEnabled =
-        this._tabList.nativeElement.scrollWidth > this._elementRef.nativeElement.offsetWidth;
+    if (this.disablePagination) {
+      this._showPaginationControls = false;
+    } else {
+      const isEnabled =
+          this._tabList.nativeElement.scrollWidth > this._elementRef.nativeElement.offsetWidth;
 
-    if (!isEnabled) {
-      this.scrollDistance = 0;
-    }
+      if (!isEnabled) {
+        this.scrollDistance = 0;
+      }
 
-    if (isEnabled !== this._showPaginationControls) {
-      this._changeDetectorRef.markForCheck();
-    }
+      if (isEnabled !== this._showPaginationControls) {
+        this._changeDetectorRef.markForCheck();
+      }
 
-    this._showPaginationControls = isEnabled;
+      this._showPaginationControls = isEnabled;
+    }
   }
 
   /**
@@ -484,10 +506,14 @@ export abstract class MatPaginatedTabHeader implements AfterContentChecked, Afte
    * should be called sparingly.
    */
   _checkScrollingControls() {
-    // Check if the pagination arrows should be activated.
-    this._disableScrollBefore = this.scrollDistance == 0;
-    this._disableScrollAfter = this.scrollDistance == this._getMaxScrollDistance();
-    this._changeDetectorRef.markForCheck();
+    if (this.disablePagination) {
+      this._disableScrollAfter = this._disableScrollBefore = true;
+    } else {
+      // Check if the pagination arrows should be activated.
+      this._disableScrollBefore = this.scrollDistance == 0;
+      this._disableScrollAfter = this.scrollDistance == this._getMaxScrollDistance();
+      this._changeDetectorRef.markForCheck();
+    }
   }
 
   /**
@@ -550,6 +576,10 @@ export abstract class MatPaginatedTabHeader implements AfterContentChecked, Afte
    * @returns Information on the current scroll distance and the maximum.
    */
   private _scrollTo(position: number) {
+    if (this.disablePagination) {
+      return {maxScrollDistance: 0, distance: 0};
+    }
+
     const maxScrollDistance = this._getMaxScrollDistance();
     this._scrollDistance = Math.max(0, Math.min(maxScrollDistance, position));
 

src/material/tabs/tab-group.html

@@ -1,6 +1,7 @@
 <mat-tab-header #tabHeader
                [selectedIndex]="selectedIndex"
                [disableRipple]="disableRipple"
+               [disablePagination]="disablePagination"
                (indexFocused)="_focusChanged($event)"
                (selectFocusedIndex)="selectedIndex = $event">
   <div class="mat-tab-label" role="tab" matTabLabelWrapper mat-ripple cdkMonitorElementFocus

src/material/tabs/tab-group.ts

@@ -59,6 +59,12 @@ export type MatTabHeaderPosition = 'above' | 'below';
 export interface MatTabsConfig {
   /** Duration for the tab animation. Must be a valid CSS value (e.g. 600ms). */
   animationDuration?: string;
+
+  /**
+   * Whether pagination should be disabled. This can be used to avoid unnecessary
+   * layout recalculations if it's known that pagination won't be required.
+   */
+  disablePagination?: boolean;
 }
 
 /** Injection token that can be used to provide the default options the tabs module. */
@@ -129,6 +135,13 @@ export abstract class _MatTabGroupBase extends _MatTabGroupMixinBase implements
   }
   private _animationDuration: string;
 
+  /**
+   * Whether pagination should be disabled. This can be used to avoid unnecessary
+   * layout recalculations if it's known that pagination won't be required.
+   */
+  @Input()
+  disablePagination: boolean;
+
   /** Background color of the tab group. */
   @Input()
   get backgroundColor(): ThemePalette { return this._backgroundColor; }
@@ -169,6 +182,8 @@ export abstract class _MatTabGroupBase extends _MatTabGroupMixinBase implements
     this._groupId = nextId++;
     this.animationDuration = defaultConfig && defaultConfig.animationDuration ?
         defaultConfig.animationDuration : '500ms';
+    this.disablePagination = defaultConfig && defaultConfig.disablePagination != null ?
+        defaultConfig.disablePagination : false;
   }
 
   /**

src/material/tabs/tab-header.spec.ts

@@ -523,6 +523,40 @@ describe('MatTabHeader', () => {
 
     });
 
+    describe('disabling pagination', () => {
+      it('should not show the pagination controls if pagination is disabled', () => {
+        fixture = TestBed.createComponent(SimpleTabHeaderApp);
+        appComponent = fixture.componentInstance;
+        appComponent.disablePagination = true;
+        fixture.detectChanges();
+        expect(appComponent.tabHeader._showPaginationControls).toBe(false);
+
+        // Add enough tabs that it will obviously exceed the width
+        appComponent.addTabsForScrolling();
+        fixture.detectChanges();
+
+        expect(appComponent.tabHeader._showPaginationControls).toBe(false);
+      });
+
+      it('should not change the scroll position if pagination is disabled', () => {
+        fixture = TestBed.createComponent(SimpleTabHeaderApp);
+        appComponent = fixture.componentInstance;
+        appComponent.disablePagination = true;
+        fixture.detectChanges();
+        appComponent.addTabsForScrolling();
+        fixture.detectChanges();
+        expect(appComponent.tabHeader.scrollDistance).toBe(0);
+
+        appComponent.tabHeader.focusIndex = appComponent.tabs.length - 1;
+        fixture.detectChanges();
+        expect(appComponent.tabHeader.scrollDistance).toBe(0);
+
+        appComponent.tabHeader.focusIndex = 0;
+        fixture.detectChanges();
+        expect(appComponent.tabHeader.scrollDistance).toBe(0);
+      });
+    });
+
     it('should re-align the ink bar when the direction changes', fakeAsync(() => {
       fixture = TestBed.createComponent(SimpleTabHeaderApp);
 
@@ -617,7 +651,8 @@ interface Tab {
   <div [dir]="dir">
     <mat-tab-header [selectedIndex]="selectedIndex" [disableRipple]="disableRipple"
                (indexFocused)="focusedIndex = $event"
-               (selectFocusedIndex)="selectedIndex = $event">
+               (selectFocusedIndex)="selectedIndex = $event"
+               [disablePagination]="disablePagination">
       <div matTabLabelWrapper class="label-content" style="min-width: 30px; width: 30px"
            *ngFor="let tab of tabs; let i = index"
            [disabled]="!!tab.disabled"
@@ -637,6 +672,7 @@ class SimpleTabHeaderApp {
   disableRipple: boolean = false;
   selectedIndex: number = 0;
   focusedIndex: number;
+  disablePagination: boolean;
   disabledTabIndex = 1;
   tabs: Tab[] = [{label: 'tab one'}, {label: 'tab one'}, {label: 'tab one'}, {label: 'tab one'}];
   dir: Direction = 'ltr';

tools/public_api_guard/material/tabs.d.ts

@@ -35,6 +35,7 @@ export declare abstract class _MatTabGroupBase extends _MatTabGroupMixinBase imp
     readonly animationDone: EventEmitter<void>;
     animationDuration: string;
     backgroundColor: ThemePalette;
+    disablePagination: boolean;
     dynamicHeight: boolean;
     readonly focusChange: EventEmitter<MatTabChangeEvent>;
     headerPosition: MatTabHeaderPosition;
@@ -191,6 +192,7 @@ export declare const matTabsAnimations: {
 
 export interface MatTabsConfig {
     animationDuration?: string;
+    disablePagination?: boolean;
 }
 
 export declare class MatTabsModule {