From 39543a3bf23b96f95677a3c0bde80d048ef1f854 Mon Sep 17 00:00:00 2001
From: Paul Gschwendtner <paulgschwendtner@gmail.com>
Date: Fri, 29 Sep 2017 22:05:08 +0200
Subject: [PATCH] fix(slider): change event is not being emitted (#7278)

* In some situations, the change event of the `<mat-slider>` is not being emitted if the user drags the thumb of the slider. This is because the `slidestart` event fires a second time before the sliding ends. This causes the slider to think that there was no value change.

Fixes #7207
---
 src/lib/slider/slider.spec.ts | 27 +++++++++++++++++++++++++++
 src/lib/slider/slider.ts      |  2 +-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/src/lib/slider/slider.spec.ts b/src/lib/slider/slider.spec.ts
index c8afaa626383..4846abddebe9 100644
--- a/src/lib/slider/slider.spec.ts
+++ b/src/lib/slider/slider.spec.ts
@@ -142,6 +142,33 @@ describe('MatSlider without forms', () => {
       expect(sliderNativeElement.classList).not.toContain('mat-slider-sliding');
     });
 
+    it('should not change value without emitting a change event', () => {
+      const onChangeSpy = jasmine.createSpy('slider onChange');
+
+      sliderInstance.change.subscribe(onChangeSpy);
+      sliderInstance.value = 50;
+      fixture.detectChanges();
+
+      dispatchSlideStartEvent(sliderNativeElement, 0, gestureConfig);
+      fixture.detectChanges();
+
+      dispatchSlideEvent(sliderNativeElement, 10, gestureConfig);
+      fixture.detectChanges();
+
+      // In some situations, HammerJS will fire a second "slidestart" event because the user
+      // holds the thumb and drags it around. This would mean that the `_valueOnSlideStart`
+      // value will be updated to the actual end value. Causing the slider to think that the value
+      // didn't change at all.
+      dispatchSlideStartEvent(sliderNativeElement, 10, gestureConfig);
+      fixture.detectChanges();
+
+      dispatchSlideEndEvent(sliderNativeElement, 10, gestureConfig);
+      fixture.detectChanges();
+
+      expect(sliderNativeElement.classList).not.toContain('mat-slider-sliding');
+      expect(onChangeSpy).toHaveBeenCalledTimes(1);
+    });
+
     it('should reset active state upon blur', () => {
       sliderInstance._isActive = true;
 
diff --git a/src/lib/slider/slider.ts b/src/lib/slider/slider.ts
index e3d2a838327a..d9cf7dadac61 100644
--- a/src/lib/slider/slider.ts
+++ b/src/lib/slider/slider.ts
@@ -492,7 +492,7 @@ export class MatSlider extends _MatSliderMixinBase
   }
 
   _onSlideStart(event: HammerInput | null) {
-    if (this.disabled) {
+    if (this.disabled || this._isSliding) {
       return;
     }