fix(select): reposition panel on scroll

Repositions the select panel after the user has scrolled, ensuring that it stays in the right place.

Author: Kristiyan Kostadinov

src/lib/select/select.spec.ts

@@ -19,14 +19,17 @@ import {Dir} from '../core/rtl/dir';
 import {
   ControlValueAccessor, FormControl, FormsModule, NG_VALUE_ACCESSOR, ReactiveFormsModule
 } from '@angular/forms';
+import {Subject} from 'rxjs/Subject';
 import {ViewportRuler} from '../core/overlay/position/viewport-ruler';
 import {dispatchFakeEvent} from '../core/testing/dispatch-events';
 import {wrappedErrorMessage} from '../core/testing/wrapped-error-message';
+import {ScrollDispatcher} from '../core/overlay/scroll/scroll-dispatcher';
 
 
 describe('MdSelect', () => {
   let overlayContainerElement: HTMLElement;
   let dir: {value: string};
+  let scrolledSubject = new Subject();
 
   beforeEach(async(() => {
     TestBed.configureTestingModule({
@@ -64,7 +67,12 @@ describe('MdSelect', () => {
         {provide: Dir, useFactory: () => {
           return dir = { value: 'ltr' };
         }},
-        {provide: ViewportRuler, useClass: FakeViewportRuler}
+        {provide: ViewportRuler, useClass: FakeViewportRuler},
+        {provide: ScrollDispatcher, useFactory: () => {
+          return {scrolled: (delay: number, callback: () => any) => {
+            return scrolledSubject.asObservable().subscribe(callback);
+          }};
+        }}
       ]
     });
 
@@ -918,7 +926,6 @@ describe('MdSelect', () => {
         checkTriggerAlignedWithOption(0);
       });
 
-
       it('should align a centered option properly when scrolled', () => {
         // Give the select enough space to open
         fixture.componentInstance.heightBelow = 400;
@@ -936,6 +943,23 @@ describe('MdSelect', () => {
         checkTriggerAlignedWithOption(4);
       });
 
+      it('should align a centered option properly when scrolling while the panel is open', () => {
+        // Give the select enough space to open
+        fixture.componentInstance.heightBelow = 400;
+        fixture.componentInstance.heightAbove = 400;
+        fixture.componentInstance.control.setValue('chips-4');
+        fixture.detectChanges();
+
+        trigger.click();
+        fixture.detectChanges();
+
+        setScrollTop(100);
+        scrolledSubject.next();
+        fixture.detectChanges();
+
+        checkTriggerAlignedWithOption(4);
+      });
+
       it('should fall back to "above" positioning properly when scrolled', () => {
         // Give the select insufficient space to open below the trigger
         fixture.componentInstance.heightBelow = 100;

src/lib/select/select.ts

@@ -28,6 +28,7 @@ import {coerceBooleanProperty} from '../core/coercion/boolean-property';
 import {ConnectedOverlayDirective} from '../core/overlay/overlay-directives';
 import {ViewportRuler} from '../core/overlay/position/viewport-ruler';
 import {SelectionModel} from '../core/selection/selection';
+import {ScrollDispatcher} from '../core/overlay/scroll/scroll-dispatcher';
 import {MdSelectDynamicMultipleError, MdSelectNonArrayValueError} from './select-errors';
 import 'rxjs/add/observable/merge';
 import 'rxjs/add/operator/startWith';
@@ -131,6 +132,9 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
   /** Subscription to tab events while overlay is focused. */
   private _tabSubscription: Subscription;
 
+  /** Subscription to global scrolled events while the select is open. */
+  private _scrolledSubscription: Subscription;
+
   /** Whether filling out the select is required in the form.  */
   private _required: boolean = false;
 
@@ -295,8 +299,10 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
 
   constructor(private _element: ElementRef, private _renderer: Renderer,
               private _viewportRuler: ViewportRuler, private _changeDetectorRef: ChangeDetectorRef,
-              @Optional() private _dir: Dir, @Self() @Optional() public _control: NgControl,
+              private _scrollDispatcher: ScrollDispatcher, @Optional() private _dir: Dir, 
+              @Self() @Optional() public _control: NgControl,
               @Attribute('tabindex') tabIndex: string) {
+
     if (this._control) {
       this._control.valueAccessor = this;
     }
@@ -344,15 +350,25 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
     this._calculateOverlayPosition();
     this._placeholderState = this._floatPlaceholderState();
     this._panelOpen = true;
+    this._scrolledSubscription = this._scrollDispatcher.scrolled(0, () => {
+      this.overlayDir.overlayRef.updatePosition();
+    });
   }
 
   /** Closes the overlay panel and focuses the host element. */
   close(): void {
     if (this._panelOpen) {
       this._panelOpen = false;
+
       if (this._selectionModel.isEmpty()) {
         this._placeholderState = '';
       }
+
+      if (this._scrolledSubscription) {
+        this._scrolledSubscription.unsubscribe();
+        this._scrolledSubscription = null;
+      }
+
       this._focusHost();
     }
   }