如何根据数组的内容有条件地渲染 React Native FlatList？

Question

I have an array completedTests in my app, with one example of its contents being this (when I use console.log() ):

Array [
  Object {
    "difference": 140,
    "id": "Practice Test 3",
    "targetReached": false,
    "testScore": "1400",
  }
]

To display its contents I would use:

<View>
<FlatList
    data={completedTests}
    keyExtractor={item => item.id}
    renderItem={({ item }) => (
           <View style={[styles.scoreOverview, { backgroundColor: '#596b96' }]}>
                <Text>{item.id}</Text>
                <Text>{item.testScore}</Text>
                <Text>{item.targetReached.toString()}</Text>
                <Text>{item.difference}</Text>
           </View>
         )} />
</View>

If the array is empty, I would set my array to be ["none"] , and trying to display this causes the following error:

undefined is not an object (evaluating 'item.targetReached.toString`)

How do I conditionally render my FlatList in the way I want?

Answer 1

Instead of setting your array to "none" use this approach

<FlatList
    data={completedTests}
    keyExtractor={item => item.id}
    ListEmptyComponent={<Text>None</Text>}
    renderItem={({ item }) => (
           <View style={[styles.scoreOverview, { backgroundColor: '#596b96' }]}>
                <Text>{item.id}</Text>
                <Text>{item.testScore}</Text>
                <Text>{item.targetReached.toString()}</Text>
                <Text>{item.difference}</Text>
           </View>
         )} />

The ListEmptyComponent would render when the array you supply is empty

Answer 2

I think this might work in what you are trying to do there...

       <View>
        {
        completedTests[0] !== "none" ? (<FlatList
            data={completedTests}
            keyExtractor={item => item.id}
            renderItem={({ item }) => (
                   <View style={[styles.scoreOverview, { backgroundColor: '#596b96' }]}>
                        <Text>{item.id}</Text>
                        <Text>{item.testScore}</Text>
                        <Text>{item.targetReached.toString()}</Text>
                        <Text>{item.difference}</Text>
                   </View>
                 )} />) : (
<Text>None</Text>
    )
        }
        </View>

so you check the array content and if it's not the ["none"] then you can render flatList else something else or nothing.