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[FlatList] shouldItemUpdate called with incorrect {item,index} #13503

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john-cfng opened this issue Apr 14, 2017 · 1 comment
Closed

[FlatList] shouldItemUpdate called with incorrect {item,index} #13503

john-cfng opened this issue Apr 14, 2017 · 1 comment
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Resolution: Locked This issue was locked by the bot.

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@john-cfng
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john-cfng commented Apr 14, 2017

Description

symptom:
supply shouldItemUpdate() and data=[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 7, 8, 9, 10, 11, ...] to a FlatList with 3 columns
shouldItemUpdate() is called with incorrect data {index: 6, item: 9}
expect {index: 6, item:7} or {index: 8, item 9}

further investigation:
seems that in FlatList.js, _shouldItemUpdate() does not take numColumns into account when calling shouldItemUpdate()

Reproduction Steps and Sample Code

obverse the values received in shouldItemUpdate()

class AppClass extends React.Component {
    constructor(props) {
        super(props)
        this.data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 7, 8, 9, 10, 11, ] ;
   }
   shouldItemUpdate(props, nextProps) {
        // some code
    }
    render() {
        return (
            <FlatList
                {...(this.modifiedProps)}
                data={this.data}
                numColumns={3}
                shouldItemUpdate={this.shouldItemUpdate}
                renderItem={this.renderItem}>
            </FlatList>
        );
    }
}

Solution

add *numColumns in _shouldItemUpdate function seems to have solved the problem

_shouldItemUpdate = (prev, next) => {  
    const {numColumns, shouldItemUpdate} = this.props;  
    if (numColumns > 1) {  
      return prev.item.length !== next.item.length ||  
        prev.item.some((prevItem, ii) => shouldItemUpdate(  
          {item: prevItem, index: prev.index*numColumns + ii},  
          {item: next.item[ii], index: next.index*numColumns + ii},  
        ));  
    } else {  
      return shouldItemUpdate(prev, next);  
    }  
  };

Additional Information

  • React Native version: 0.43.2
  • Platform: Android 4.1.2 & 7.1.1
  • Development Operating System: Win10
  • Dev tools: Android SDK Tools 26.0.1
@hramos hramos changed the title FlatList: shouldItemUpdate called with incorrect {item,index} [FlatList] shouldItemUpdate called with incorrect {item,index} Apr 25, 2017
@hramos hramos added the Icebox label Jul 25, 2017
@hramos
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hramos commented Jul 25, 2017

Hi there! This issue is being closed because it has been inactive for a while. Maybe the issue has been fixed in a recent release, or perhaps it is not affecting a lot of people. Either way, we're automatically closing issues after a period of inactivity. Please do not take it personally!

If you think this issue should definitely remain open, please let us know. The following information is helpful when it comes to determining if the issue should be re-opened:

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@hramos hramos closed this as completed Jul 25, 2017
@facebook facebook locked as resolved and limited conversation to collaborators Jul 25, 2018
@react-native-bot react-native-bot added the Resolution: Locked This issue was locked by the bot. label Jul 25, 2018
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