fix(select): selected option not being highlighted when options are added asynchronously (#2499)

* fix(select): selected option not being highlighted when options are added asynchronously

Fixes the select component not highlighting the model value when the options get added after initialization.

Fixes #2497.

* Address the feedback.

* Fix linter errors.

src/lib/select/select.spec.ts

@@ -16,7 +16,14 @@ describe('MdSelect', () => {
   beforeEach(async(() => {
     TestBed.configureTestingModule({
       imports: [MdSelectModule.forRoot(), ReactiveFormsModule, FormsModule],
-      declarations: [BasicSelect, NgModelSelect, ManySelects, NgIfSelect, SelectWithChangeEvent],
+      declarations: [
+        BasicSelect,
+        NgModelSelect,
+        ManySelects,
+        NgIfSelect,
+        SelectInitWithoutOptions,
+        SelectWithChangeEvent
+      ],
       providers: [
         {provide: OverlayContainer, useFactory: () => {
           overlayContainerElement = document.createElement('div') as HTMLElement;
@@ -239,6 +246,27 @@ describe('MdSelect', () => {
 
   });
 
+  it('should select the proper option when the list of options is initialized at a later point',
+    async(() => {
+      let fixture = TestBed.createComponent(SelectInitWithoutOptions);
+      let instance = fixture.componentInstance;
+
+      fixture.detectChanges();
+
+      // Wait for the initial writeValue promise.
+      fixture.whenStable().then(() => {
+        expect(instance.select.selected).toBeFalsy();
+
+        instance.addOptions();
+        fixture.detectChanges();
+
+        // Wait for the next writeValue promise.
+        fixture.whenStable().then(() => {
+          expect(instance.select.selected).toBe(instance.options.toArray()[1]);
+        });
+      });
+    }));
+
   describe('forms integration', () => {
     let fixture: ComponentFixture<BasicSelect>;
     let trigger: HTMLElement;
@@ -1267,7 +1295,6 @@ class ManySelects {}
       </md-select>
     </div>
   `,
-
 })
 class NgIfSelect {
   isShowing = false;
@@ -1304,6 +1331,32 @@ class SelectWithChangeEvent {
   changeListener = jasmine.createSpy('MdSelect change listener');
 }
 
+@Component({
+  selector: 'select-init-without-options',
+  template: `
+    <md-select placeholder="Food I want to eat right now" [formControl]="control">
+      <md-option *ngFor="let food of foods" [value]="food.value">
+        {{ food.viewValue }}
+      </md-option>
+    </md-select>
+  `
+})
+class SelectInitWithoutOptions {
+  foods: any[];
+  control = new FormControl('pizza-1');
+
+  @ViewChild(MdSelect) select: MdSelect;
+  @ViewChildren(MdOption) options: QueryList<MdOption>;
+
+  addOptions() {
+    this.foods = [
+      { value: 'steak-0', viewValue: 'Steak' },
+      { value: 'pizza-1', viewValue: 'Pizza' },
+      { value: 'tacos-2', viewValue: 'Tacos'}
+    ];
+  }
+}
+
 /**
  * TODO: Move this to core testing utility until Angular has event faking
  * support.

src/lib/select/select.ts

@@ -241,7 +241,15 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
   ngAfterContentInit() {
     this._initKeyManager();
     this._resetOptions();
-    this._changeSubscription = this.options.changes.subscribe(() => this._resetOptions());
+    this._changeSubscription = this.options.changes.subscribe(() => {
+      this._resetOptions();
+
+      if (this._control) {
+        // Defer setting the value in order to avoid the "Expression
+        // has changed after it was checked" errors from Angular.
+        Promise.resolve(null).then(() => this._setSelectionByValue(this._control.value));
+      }
+    });
   }
 
   ngOnDestroy() {