fix(list): selection list always firing change event for selectAll and deselectAll (#11029)

src/lib/list/selection-list.spec.ts

@@ -751,6 +751,30 @@ describe('MatSelectionList with forms', () => {
       expect(fixture.componentInstance.selectedOptions).toEqual(['opt1']);
     }));
 
+    it('should not dispatch the model change event if nothing changed using selectAll', () => {
+      expect(fixture.componentInstance.modelChangeSpy).not.toHaveBeenCalled();
+
+      selectionListDebug.componentInstance.selectAll();
+      fixture.detectChanges();
+
+      expect(fixture.componentInstance.modelChangeSpy).toHaveBeenCalledTimes(1);
+
+      selectionListDebug.componentInstance.selectAll();
+      fixture.detectChanges();
+
+      expect(fixture.componentInstance.modelChangeSpy).toHaveBeenCalledTimes(1);
+    });
+
+    it('should not dispatch the model change event if nothing changed using selectAll', () => {
+      expect(fixture.componentInstance.modelChangeSpy).not.toHaveBeenCalled();
+
+      selectionListDebug.componentInstance.deselectAll();
+      fixture.detectChanges();
+
+      expect(fixture.componentInstance.modelChangeSpy).not.toHaveBeenCalled();
+    });
+
+
   });
 
   describe('and formControl', () => {
@@ -968,13 +992,14 @@ class SelectionListWithTabindexBinding {
 
 @Component({
   template: `
-    <mat-selection-list [(ngModel)]="selectedOptions">
+    <mat-selection-list [(ngModel)]="selectedOptions" (ngModelChange)="modelChangeSpy()">
       <mat-list-option value="opt1">Option 1</mat-list-option>
       <mat-list-option value="opt2">Option 2</mat-list-option>
       <mat-list-option value="opt3" *ngIf="renderLastOption">Option 3</mat-list-option>
     </mat-selection-list>`
 })
 class SelectionListWithModel {
+  modelChangeSpy = jasmine.createSpy('model change spy');
   selectedOptions: string[] = [];
   renderLastOption = true;
 }

src/lib/list/selection-list.ts

@@ -221,10 +221,10 @@ export class MatListOption extends _MatListOptionMixinBase
     return this._element.nativeElement;
   }
 
-  /** Sets the selected state of the option. */
-  _setSelected(selected: boolean) {
+  /** Sets the selected state of the option. Returns whether the value has changed. */
+  _setSelected(selected: boolean): boolean {
     if (selected === this._selected) {
-      return;
+      return false;
     }
 
     this._selected = selected;
@@ -236,6 +236,7 @@ export class MatListOption extends _MatListOptionMixinBase
     }
 
     this._changeDetector.markForCheck();
+    return true;
   }
 }
 
@@ -302,7 +303,6 @@ export class MatSelectionList extends _MatSelectionListMixinBase implements Focu
 
   constructor(private _element: ElementRef, @Attribute('tabindex') tabIndex: string) {
     super();
-
     this.tabIndex = parseInt(tabIndex) || 0;
   }
 
@@ -346,14 +346,12 @@ export class MatSelectionList extends _MatSelectionListMixinBase implements Focu
 
   /** Selects all of the options. */
   selectAll() {
-    this.options.forEach(option => option._setSelected(true));
-    this._reportValueChange();
+    this._setAllOptionsSelected(true);
   }
 
   /** Deselects all of the options. */
   deselectAll() {
-    this.options.forEach(option => option._setSelected(false));
-    this._reportValueChange();
+    this._setAllOptionsSelected(false);
   }
 
   /** Sets the focused option of the selection-list. */
@@ -479,6 +477,26 @@ export class MatSelectionList extends _MatSelectionListMixinBase implements Focu
     }
   }
 
+  /**
+   * Sets the selected state on all of the options
+   * and emits an event if anything changed.
+   */
+  private _setAllOptionsSelected(isSelected: boolean) {
+    // Keep track of whether anything changed, because we only want to
+    // emit the changed event when something actually changed.
+    let hasChanged = false;
+
+    this.options.forEach(option => {
+      if (option._setSelected(isSelected)) {
+        hasChanged = true;
+      }
+    });
+
+    if (hasChanged) {
+      this._reportValueChange();
+    }
+  }
+
   /**
    * Utility to ensure all indexes are valid.
    * @param index The index to be checked.