fix(button-toggle): changed after checked error for repeated toggles with a preselected value

src/lib/button-toggle/button-toggle.spec.ts

@@ -1,7 +1,7 @@
 import {fakeAsync, tick, ComponentFixture, TestBed} from '@angular/core/testing';
 import {dispatchMouseEvent} from '@angular/cdk/testing';
 import {NgModel, FormsModule, ReactiveFormsModule, FormControl} from '@angular/forms';
-import {Component, DebugElement} from '@angular/core';
+import {Component, DebugElement, ViewChild, ViewChildren, QueryList} from '@angular/core';
 import {By} from '@angular/platform-browser';
 import {
   MatButtonToggleGroup,
@@ -209,6 +209,7 @@ describe('MatButtonToggle without forms', () => {
         StandaloneButtonToggle,
         ButtonToggleWithAriaLabel,
         ButtonToggleWithAriaLabelledby,
+        RepeatedButtonTogglesWithPreselectedValue,
       ],
     });
 
@@ -662,6 +663,14 @@ describe('MatButtonToggle without forms', () => {
       expect(inputElement.getAttribute('aria-labelledby')).toBe(null);
     });
   });
+
+  it('should not throw on init when toggles are repeated and there is an initial value', () => {
+    const fixture = TestBed.createComponent(RepeatedButtonTogglesWithPreselectedValue);
+
+    expect(() => fixture.detectChanges()).not.toThrow();
+    expect(fixture.componentInstance.toggleGroup.value).toBe('Two');
+    expect(fixture.componentInstance.toggles.toArray()[1].checked).toBe(true);
+  });
 });
 
 @Component({
@@ -759,3 +768,21 @@ class ButtonToggleWithAriaLabel { }
   template: `<mat-button-toggle aria-labelledby="some-id"></mat-button-toggle>`
 })
 class ButtonToggleWithAriaLabelledby {}
+
+
+@Component({
+  template: `
+    <mat-button-toggle-group [(value)]="value">
+      <mat-button-toggle *ngFor="let toggle of possibleValues" [value]="toggle">
+        {{toggle}}
+      </mat-button-toggle>
+    </mat-button-toggle-group>
+  `
+})
+class RepeatedButtonTogglesWithPreselectedValue {
+  @ViewChild(MatButtonToggleGroup) toggleGroup: MatButtonToggleGroup;
+  @ViewChildren(MatButtonToggle) toggles: QueryList<MatButtonToggle>;
+
+  possibleValues = ['One', 'Two', 'Three'];
+  value = 'Two';
+}

src/lib/button-toggle/button-toggle.ts

@@ -180,14 +180,8 @@ export class MatButtonToggleGroup extends _MatButtonToggleGroupMixinBase impleme
   }
 
   ngAfterContentInit() {
-    // If there was an attempt to assign a value before init, use it to set the
-    // initial selection, otherwise check the `checked` state of the toggles.
-    if (typeof this._tempValue !== 'undefined') {
-      this._setSelectionByValue(this._tempValue);
-      this._tempValue = undefined;
-    } else {
-      this._selectionModel.select(...this._buttonToggles.filter(toggle => toggle.checked));
-    }
+    this._selectionModel.select(...this._buttonToggles.filter(toggle => toggle.checked));
+    this._tempValue = undefined;
   }
 
   /**
@@ -261,6 +255,19 @@ export class MatButtonToggleGroup extends _MatButtonToggleGroupMixinBase impleme
     return this._selectionModel.isSelected(toggle);
   }
 
+  /** Determines whether a button toggle should be checked on init. */
+  _isPrechecked(toggle: MatButtonToggle) {
+    if (typeof this._tempValue === 'undefined') {
+      return false;
+    }
+
+    if (this.multiple && Array.isArray(this._tempValue)) {
+      return !!this._tempValue.find(value => toggle.value != null && value === toggle.value);
+    }
+
+    return toggle.value === this._tempValue;
+  }
+
   /** Updates the selection state of the toggles in the group based on a value. */
   private _setSelectionByValue(value: any|any[]) {
     // If the toggles haven't been initialized yet, save the value for later.
@@ -409,6 +416,10 @@ export class MatButtonToggle extends _MatButtonToggleMixinBase implements OnInit
       this.name = this.buttonToggleGroup.name;
     }
 
+    if (this.buttonToggleGroup && this.buttonToggleGroup._isPrechecked(this)) {
+      this.checked = true;
+    }
+
     this._focusMonitor.monitor(this._elementRef.nativeElement, true);
   }
 
@@ -449,8 +460,8 @@ export class MatButtonToggle extends _MatButtonToggleMixinBase implements OnInit
    * update bound properties of the radio button.
    */
   _markForCheck() {
-    // When group value changes, the button will not be notified. Use `markForCheck` to explicit
-    // update button toggle's status
+    // When the group value changes, the button will not be notified.
+    // Use `markForCheck` to explicit update button toggle's status.
     this._changeDetectorRef.markForCheck();
   }
 }