From e9f95c1a7d08d34640625e4db362f73e29385cb3 Mon Sep 17 00:00:00 2001
From: Brent Vatne <brentvatne@gmail.com>
Date: Thu, 28 Jan 2016 15:10:59 -0800
Subject: [PATCH] Check for contentView before emitting scroll event

Summary:
I've found that when switching between tabs that each have ScrollViews, sometimes `emitScrollEvent` fires without a `contentView`, which causes the following crash:

```
`D/AndroidRuntime(24496): Shutting down VM
E/AndroidRuntime(24496): FATAL EXCEPTION: main
E/AndroidRuntime(24496): Process: com.listexp, PID: 24496
E/AndroidRuntime(24496): java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getWidth()' on a null object reference
E/AndroidRuntime(24496):        at com.facebook.react.views.scroll.ReactScrollViewHelper.emitScrollEvent(ReactScrollViewHelper.java:59)
E/AndroidRuntime(24496):        at com.facebook.react.views.scroll.ReactScrollViewHelper.emitScrollMomentumEndEvent(ReactScrollViewHelper.java:46)
E/AndroidRuntime(24496):        at com.facebook.react.views.scroll.ReactScrollView$1.run(ReactScrollView.java:159)
E/AndroidRuntime(24496):        at android.os.Handler.handleCallback(Handler.java:739)
E/AndroidRuntime(24496):        at android.os.Handler.disp
Closes https://github.com/facebook/react-native/pull/5561

Reviewed By: svcscm

Differential Revision: D2876385

Pulled By: androidtrunkagent

fb-gh-sync-id: 33406eaa96352d5adae857088da09fb446b68440
---
 .../facebook/react/views/scroll/ReactScrollViewHelper.java   | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewHelper.java b/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewHelper.java
index 1b9c3eb7d..3ee46350d 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewHelper.java
+++ b/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewHelper.java
@@ -48,6 +48,11 @@ public class ReactScrollViewHelper {
 
   private static void emitScrollEvent(ViewGroup scrollView, ScrollEventType scrollEventType) {
     View contentView = scrollView.getChildAt(0);
+
+    if (contentView == null) {
+      return;
+    }
+
     ReactContext reactContext = (ReactContext) scrollView.getContext();
     reactContext.getNativeModule(UIManagerModule.class).getEventDispatcher().dispatchEvent(
         ScrollEvent.obtain(