fix(checkbox): Emit event when checkbox's indeterminate value changes (#2130)

* Emit event when checkbox indeterminate value changes

* Add test

* Use boolean and emit indeterminate only if value changed

src/lib/checkbox/checkbox.spec.ts

@@ -104,6 +104,39 @@ describe('MdCheckbox', () => {
       expect(inputElement.indeterminate).toBe(false);
     });
 
+    it('should set indeterminate to false when set checked', () => {
+      testComponent.isIndeterminate = true;
+      fixture.detectChanges();
+
+      expect(checkboxInstance.indeterminate).toBe(true);
+      expect(inputElement.indeterminate).toBe(true);
+      expect(testComponent.isIndeterminate).toBe(true);
+
+      testComponent.isChecked = true;
+      fixture.detectChanges();
+
+      expect(checkboxInstance.checked).toBe(true);
+      expect(inputElement.indeterminate).toBe(false);
+      expect(inputElement.checked).toBe(true);
+      expect(testComponent.isIndeterminate).toBe(false);
+
+      testComponent.isIndeterminate = true;
+      fixture.detectChanges();
+
+      expect(checkboxInstance.indeterminate).toBe(true);
+      expect(inputElement.indeterminate).toBe(true);
+      expect(inputElement.checked).toBe(true);
+      expect(testComponent.isIndeterminate).toBe(true);
+
+      testComponent.isChecked = false;
+      fixture.detectChanges();
+
+      expect(checkboxInstance.checked).toBe(false);
+      expect(inputElement.indeterminate).toBe(false);
+      expect(inputElement.checked).toBe(false);
+      expect(testComponent.isIndeterminate).toBe(false);
+    });
+
     it('should change native element checked when check programmatically', () => {
       expect(inputElement.checked).toBe(false);
 
@@ -627,7 +660,7 @@ describe('MdCheckbox', () => {
         [required]="isRequired"
         [labelPosition]="labelPos"
         [checked]="isChecked"
-        [indeterminate]="isIndeterminate"
+        [(indeterminate)]="isIndeterminate"
         [disabled]="isDisabled"
         [color]="checkboxColor"
         (change)="changeCount = changeCount + 1"

src/lib/checkbox/checkbox.ts

@@ -147,6 +147,9 @@ export class MdCheckbox implements ControlValueAccessor {
   /** Event emitted when the checkbox's `checked` value changes. */
   @Output() change: EventEmitter<MdCheckboxChange> = new EventEmitter<MdCheckboxChange>();
 
+  /** Event emitted when the checkbox's `indeterminate` value changes. */
+  @Output() indeterminateChange: EventEmitter<boolean> = new EventEmitter<boolean>();
+
   /** The native `<input type="checkbox"> element */
   @ViewChild('input') _inputElement: ElementRef;
 
@@ -186,7 +189,10 @@ export class MdCheckbox implements ControlValueAccessor {
 
   set checked(checked: boolean) {
     if (checked != this.checked) {
-      this._indeterminate = false;
+      if (this._indeterminate) {
+        this._indeterminate = false;
+        this.indeterminateChange.emit(this._indeterminate);
+      }
       this._checked = checked;
       this._transitionCheckState(
           this._checked ? TransitionCheckState.Checked : TransitionCheckState.Unchecked);
@@ -208,6 +214,7 @@ export class MdCheckbox implements ControlValueAccessor {
   }
 
   set indeterminate(indeterminate: boolean) {
+    let changed =  indeterminate != this._indeterminate;
     this._indeterminate = indeterminate;
     if (this._indeterminate) {
       this._transitionCheckState(TransitionCheckState.Indeterminate);
@@ -215,6 +222,9 @@ export class MdCheckbox implements ControlValueAccessor {
       this._transitionCheckState(
           this.checked ? TransitionCheckState.Checked : TransitionCheckState.Unchecked);
     }
+    if (changed) {
+      this.indeterminateChange.emit(this._indeterminate);
+    }
   }
 
   /** The color of the button. Can be `primary`, `accent`, or `warn`. */