FlatList onScroll corner case bug: contentOffset undefined #15725
Description
Environment
react-native -v: 0.45.1node -v: 7.0npm -v: 3.10
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Target Platform: iOS 10.2
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Development Operating System: OSX 10.12
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Build tools: react-native & Xcode
Steps to Reproduce
This is a corner case bug that happens sporadically in a production build. It hasn't happened yet in a debug build. In the onScroll callback for FlatList, the argument passed in is incomplete. event.nativeEvent.contentOffset is undefined. The crash report came from NewRelic:
RCTFatalException: Unhandled JS Exception: undefined is not an object (evaluating 'e.y')
in 0x1000f3ea0 0 + 4295966368
Unhandled JS Exception: undefined is not an object (evaluating 'e.y'), stack: value@304:8561 value@304:6956 u@94:142 invokeGuardedCallbackAndCatchFirstError@94:580 c@110:365 a@110:567 v@154:502 i@157:95 processEventQueue@154:1433 s@165:88 handleTopLevel@165:174 <unknown>@164:574 perform@185:596 u@108:150 _receiveRootNodeIDEvent@164:546 receiveEvent@164:656 value@22:2893 <unknown>@22:832 value@22:2294 value@22:804
There is only one line in our app that references a .y key:
onScroll(event) {
let newScrollOffset = event.nativeEvent.contentOffset.y;
// ...
}
FlatList is instantiated as:
<FlatList
keyboardShouldPersistTaps={'handled'}
removeClippedSubviews={true}
data={this.state.listData}
extraData={this.state.dataFilter}
renderItem={this.renderSomething}
keyExtractor={(item, index) => item.id}
ListHeaderComponent={this.renderHeader(this.state.headerState)}
onScroll={this.onScroll.bind(this)}
scrollEventThrottle={100}
onRefresh={this.renderRefresh}
refreshing={this.state.refreshing}
/>
Expected Behavior
contentOffset should be a valid object.
Actual Behavior
contentOffset is undefined. Is it possible for contentOffset to be undefined in the event parameter?
Reproducible Demo
Won't reproduce in a debugger.