fix(datepicker): prevent matInput from clobbering date value

src/demo-app/datepicker/datepicker-demo.html

@@ -121,3 +121,15 @@ <h2>Input disabled, datepicker popup enabled</h2>
                    [startView]="yearView ? 'year' : 'month'"></mat-datepicker>
   </mat-form-field>
 </p>
+
+<h2>Datepicker with value property binding</h2>
+<p>
+  <mat-datepicker-toggle [for]="datePicker4"></mat-datepicker-toggle>
+  <mat-form-field>
+    <input matInput [matDatepicker]="datePicker4" [value]="date" [min]="minDate"
+           [max]="maxDate" [matDatepickerFilter]="filterOdd ? dateFilter : null"
+           placeholder="Value binding">
+    <mat-datepicker #datePicker4 [touchUi]="touch" [startAt]="startAt"
+                    [startView]="yearView ? 'year' : 'month'"></mat-datepicker>
+  </mat-form-field>
+</p>

src/lib/datepicker/datepicker-input.ts

@@ -19,7 +19,7 @@ import {
   OnDestroy,
   Optional,
   Output,
-  Renderer2,
+  Renderer2
 } from '@angular/core';
 import {
   AbstractControl,
@@ -29,10 +29,11 @@ import {
   ValidationErrors,
   Validator,
   ValidatorFn,
-  Validators,
+  Validators
 } from '@angular/forms';
 import {DateAdapter, MAT_DATE_FORMATS, MatDateFormats} from '@angular/material/core';
 import {MatFormField} from '@angular/material/form-field';
+import {MAT_INPUT_VALUE_ACCESSOR} from '@angular/material/input';
 import {Subscription} from 'rxjs/Subscription';
 import {coerceDateProperty} from './coerce-date-property';
 import {MatDatepicker} from './datepicker';
@@ -71,7 +72,11 @@ export class MatDatepickerInputEvent<D> {
 /** Directive used to connect an input to a MatDatepicker. */
 @Directive({
   selector: 'input[matDatepicker]',
-  providers: [MAT_DATEPICKER_VALUE_ACCESSOR, MAT_DATEPICKER_VALIDATORS],
+  providers: [
+    MAT_DATEPICKER_VALUE_ACCESSOR,
+    MAT_DATEPICKER_VALIDATORS,
+    {provide: MAT_INPUT_VALUE_ACCESSOR, useExisting: MatDatepickerInput},
+  ],
   host: {
     '[attr.aria-haspopup]': 'true',
     '[attr.aria-owns]': '(_datepicker?.opened && _datepicker.id) || null',

src/lib/datepicker/datepicker.spec.ts

@@ -30,6 +30,8 @@ import {MatDatepickerIntl, MatDatepickerModule} from './index';
 
 
 describe('MatDatepicker', () => {
+  const SUPPORTS_INTL = typeof Intl != 'undefined';
+
   afterEach(inject([OverlayContainer], (container: OverlayContainer) => {
     container.getContainerElement().parentNode!.removeChild(container.getContainerElement());
   }));
@@ -82,6 +84,12 @@ describe('MatDatepicker', () => {
         fixture.detectChanges();
       }));
 
+      it('should initialize with correct value shown in input', () => {
+        if (SUPPORTS_INTL) {
+          expect(fixture.nativeElement.querySelector('input').value).toBe('1/1/2020');
+        }
+      });
+
       it('open non-touch should open popup', () => {
         expect(document.querySelector('.cdk-overlay-pane.mat-datepicker-popup')).toBeNull();
 

src/lib/input/input-value-accessor.ts

@@ -0,0 +1,19 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {InjectionToken} from '@angular/core';
+
+
+/**
+ * This token is used to inject the object whose value should be set into `MatInput`. If none is
+ * provided, the native `HTMLInputElement` is used. Directives like `MatDatepickerInput` can provide
+ * themselves for this token, in order to make `MatInput` delegate the getting and setting of the
+ * value to them.
+ */
+export const MAT_INPUT_VALUE_ACCESSOR =
+    new InjectionToken<{value: any}>('MAT_INPUT_VALUE_ACCESSOR');

src/lib/input/input.ts

@@ -6,24 +6,26 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import {coerceBooleanProperty} from '@angular/cdk/coercion';
+import {getSupportedInputTypes, Platform} from '@angular/cdk/platform';
 import {
   Directive,
   DoCheck,
   ElementRef,
+  Inject,
   Input,
   OnChanges,
   OnDestroy,
   Optional,
   Renderer2,
-  Self,
+  Self
 } from '@angular/core';
-import {coerceBooleanProperty} from '@angular/cdk/coercion';
-import {FormGroupDirective, NgControl, NgForm, FormControl} from '@angular/forms';
-import {Platform, getSupportedInputTypes} from '@angular/cdk/platform';
-import {getMatInputUnsupportedTypeError} from './input-errors';
+import {FormControl, FormGroupDirective, NgControl, NgForm} from '@angular/forms';
 import {ErrorStateMatcher} from '@angular/material/core';
-import {Subject} from 'rxjs/Subject';
 import {MatFormFieldControl} from '@angular/material/form-field';
+import {Subject} from 'rxjs/Subject';
+import {getMatInputUnsupportedTypeError} from './input-errors';
+import {MAT_INPUT_VALUE_ACCESSOR} from './input-value-accessor';
 
 // Invalid input type. Using one of these will throw an MatInputUnsupportedTypeError.
 const MAT_INPUT_INVALID_TYPES = [
@@ -70,7 +72,7 @@ export class MatInput implements MatFormFieldControl<any>, OnChanges, OnDestroy,
   protected _required = false;
   protected _id: string;
   protected _uid = `mat-input-${nextUniqueId++}`;
-  protected _previousNativeValue = this.value;
+  protected _previousNativeValue: any;
   private _readonly = false;
 
   /** Whether the input is focused. */
@@ -129,10 +131,10 @@ export class MatInput implements MatFormFieldControl<any>, OnChanges, OnDestroy,
 
   /** The input element's value. */
   @Input()
-  get value() { return this._elementRef.nativeElement.value; }
-  set value(value: string) {
+  get value(): any { return this._inputValueAccessor.value; }
+  set value(value: any) {
     if (value !== this.value) {
-      this._elementRef.nativeElement.value = value;
+      this._inputValueAccessor.value = value;
       this.stateChanges.next();
     }
   }
@@ -157,7 +159,14 @@ export class MatInput implements MatFormFieldControl<any>, OnChanges, OnDestroy,
               @Optional() @Self() public ngControl: NgControl,
               @Optional() protected _parentForm: NgForm,
               @Optional() protected _parentFormGroup: FormGroupDirective,
-              private _defaultErrorStateMatcher: ErrorStateMatcher) {
+              private _defaultErrorStateMatcher: ErrorStateMatcher,
+              @Optional() @Self() @Inject(MAT_INPUT_VALUE_ACCESSOR)
+                  private _inputValueAccessor: {value: any}) {
+    // If no input value accessor was explicitly specified, use the element as the input value
+    // accessor.
+    this._inputValueAccessor = this._inputValueAccessor || this._elementRef.nativeElement;
+
+    this._previousNativeValue = this.value;
 
     // Force setter to be called in case id was not specified.
     this.id = this.id;

src/lib/input/public-api.ts

@@ -11,5 +11,5 @@ export * from './input-module';
 export * from './autosize';
 export * from './input';
 export * from './input-errors';
-
+export * from './input-value-accessor';