fix(radio): Uncheck radio group if uncheck radio button programmatically (#1561)

* added test cases for uncheck
* notify all radio buttons after status change and radio group value change to avoid notify radio group twice

Fixes #609

Author: tinayuangao

src/lib/radio/radio.spec.ts

@@ -233,6 +233,44 @@ describe('MdRadio', () => {
           .toBe(0, 'Expect no [md-ripple] in radio buttons');
       }
     }));
+
+    it('should update the group\'s selected radio to null when unchecking that radio '
+        + 'programmatically', () => {
+      let changeSpy = jasmine.createSpy('radio-group change listener');
+      groupInstance.change.subscribe(changeSpy);
+      radioInstances[0].checked = true;
+
+      fixture.detectChanges();
+
+      expect(changeSpy).toHaveBeenCalled();
+      expect(groupInstance.value).toBeTruthy();
+
+      radioInstances[0].checked = false;
+
+      fixture.detectChanges();
+
+      expect(changeSpy).toHaveBeenCalledTimes(2);
+      expect(groupInstance.value).toBeFalsy();
+      expect(radioInstances.every(radio => !radio.checked)).toBe(true);
+      expect(groupInstance.selected).toBeNull();
+    });
+
+    it('should fire a change event from the group whenever a radio checked state changes', () => {
+      let changeSpy = jasmine.createSpy('radio-group change listener');
+      groupInstance.change.subscribe(changeSpy);
+      radioInstances[0].checked = true;
+
+      fixture.detectChanges();
+
+      expect(changeSpy).toHaveBeenCalled();
+      expect(groupInstance.value).toBeTruthy();
+
+      radioInstances[1].checked = true;
+
+      fixture.detectChanges();
+
+      expect(changeSpy).toHaveBeenCalledTimes(2);
+    });
   });
 
   describe('group with ngModel', () => {

src/lib/radio/radio.ts

@@ -306,15 +306,19 @@ export class MdRadioButton implements OnInit {
   }
 
   set checked(newCheckedState: boolean) {
-    if (newCheckedState) {
-      // Notify all radio buttons with the same name to un-check.
-      this.radioDispatcher.notify(this.id, this.name);
-    }
-
     this._checked = newCheckedState;
 
     if (newCheckedState && this.radioGroup && this.radioGroup.value != this.value) {
       this.radioGroup.selected = this;
+    } else if (!newCheckedState && this.radioGroup && this.radioGroup.value == this.value) {
+      // When unchecking the selected radio button, update the selected radio
+      // property on the group.
+      this.radioGroup.selected = null;
+    }
+
+    if (newCheckedState) {
+      // Notify all radio buttons with the same name to un-check.
+      this.radioDispatcher.notify(this.id, this.name);
     }
   }