Flatlist renders mapped data thrice in React Native

user_9343113 0
Viewed 69

I have been using map function to render data with Flatlist in my React Native application. But the same data is being rendered thrice for some reason. Here's what I have right now:

    renderItem = ({ item, index }) => {
        if (item === null) return <View key="post_" />;
        const imageURI = this.props.categories;
        const mainCategories = imageURI.filter(
            category => category.parent === 0
        );
        return mainCategories.map((data) => {
            return (
                <TouchableOpacity
                  activeOpacity={0.9}
                  style={[styles.panelTwo]}
                  onPress={() => this.onRowClickHandle(item)}
                >
                 <ImageCache uri={data.image === null ? Images.defaultPayment : data.image.src} key={data.id} style={styles.imagePanelTwo} />
                 <Text numberOfLines={1} style={styles.nameTwo}>
                  {data.name}
                 </Text>
                </TouchableOpacity>
            );
        })
    };
  
    render() {
        const {categories,showSorting} = this.props;
        const mainCategories = this.props.categories.filter(
            category => category.parent === 0
        );
        return (
          <View>
           <View style={[styles.flatWrap]}>
            <FlatList
              contentContainerStyle={styles.flatlist}
              data={mainCategories}
              keyExtractor={item => `post__${item.id}`}
              renderItem={this.renderItem}
              showsHorizontalScrollIndicator={false}
              horizontal
            />
          </View>
        </View>
        );
    }
}

I can't figure out why the same data is rendering thrice in this situation. Also the mainCategories is like this:

enter image description here

except that it's showing three times.

flatlist react-native javascript
2 Answers

Let's say your data array is [1, 2, 3]. In this case, FlatList will loop over it and renders them one by one and will look like:

<Text>1</Text>
<Text>2</Text>
<Text>3</Text>

But in renderItem you do the loop again and say, render the whole array for every row and your result is:

<Text>1</Text>
<Text>2</Text>
<Text>3</Text>

<Text>1</Text>
<Text>2</Text>
<Text>3</Text>

<Text>1</Text>
<Text>2</Text>
<Text>3</Text>
user_84540550

Change

    renderItem = ({ item, index }) => {
        if (item === null) return <View key="post_" />;
        const imageURI = this.props.categories;
        const mainCategories = imageURI.filter(
            category => category.parent === 0
        );
        return mainCategories.map((data) => {
            return (
                <TouchableOpacity
                  activeOpacity={0.9}
                  style={[styles.panelTwo]}
                  onPress={() => this.onRowClickHandle(item)}
                >
                 <ImageCache uri={data.image === null ? Images.defaultPayment : data.image.src} key={data.id} style={styles.imagePanelTwo} />
                 <Text numberOfLines={1} style={styles.nameTwo}>
                  {data.name}
                 </Text>
                </TouchableOpacity>
            );
        })
    };

To

    renderItem = ({ item }) => {
        if (item === null) return <View key="post_" />;
        const onPressItem = () => this.onRowClickHandle(item)
        return (
            <TouchableOpacity
              activeOpacity={0.9}
              style={styles.panelTwo}
              onPress={onPressItem}
            >
             <ImageCache uri={data.image?.src || Images.defaultPayment} key={data.id} style={styles.imagePanelTwo} />
             <Text numberOfLines={1} style={styles.nameTwo}>{data.name}</Text>
           </TouchableOpacity>
        );
    };
user_61345670
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