如何显示 activity 指示器，直到使用 redux 从 firestore 中获取并显示在反应本机中的所有数据

Question

我在使用 Redux 的反应本机应用程序中使用 FireBase 作为数据库。在获取数据之前，我想显示一个 Activity 指示器。我的 Redux 操作是：

export const fetchproducts=()=>{
    return  async dispatch=>{
       const items = []
       const db = firebase.firestore();
       db.collection("Shops").collection('products').get().then((querySnapshot)=> {
           querySnapshot.forEach((doc,i)=> {  
              items.push(new Product(
                  doc.id, 
                  doc.data().name, 
                  doc.data().description, 
                  doc.data().price, 
               ))
           });   
           dispatch({
              type:SET_PRODUCTS,
              products:items
           })
   }).catch((err)=>{
         throw err
      })
  }
 }

我的 React Native js 代码是：

const ProductsOverviewScreen = props => {
      const [isLoading,setIsLoading]=useState(false)
      const [isRefreshing,setIsRefreshing]=useState(false)
      const allshops = useSelector(state => state.shops.allshops);
      const [error,setError]=useState()
      const products = useSelector(state => state.products.availableProducts);
      const dispatch = useDispatch();

      const loadProducts=useCallback( async ()=>{
            setError(null)
            setIsLoading(true)
            try{
                await dispatch(productActons.fetchproducts())
            }catch(err){
                setError(err.message)
            }
            setIsLoading(false)
      },[dispatch,setIsLoading,setError])

      useEffect(()=>{
          const willFocusSub=props.navigation.addListener('willFocus',()=>{
          loadProducts()
      })
       return ()=>{
         willFocusSub.remove()
       }
       },[loadProducts])


      useEffect(()=>{
         loadProducts()
      },[dispatch,loadProducts])

    if(error)
      {
       return <View style={{flex:1,alignItems:'center',justifyContent:'center'}}>
                 <Text>An error Occured </Text>
                 <Button title="Try Again" onPress={loadProducts} color={Colors.primary}></Button>
              </View>
      }  

     if(isLoading){
         return <View style={{flex:1,alignItems:'center',justifyContent:'center'}}>
                    <ActivityIndicator size="large" color={Colors.primary}/>
                </View>
      }

     if(!isLoading&&products.length===0)
         {
          return <View style={{flex:1,alignItems:'center',justifyContent:'center'}}>
                     <Text>No Products</Text></View>
         }

      return (
              <View>
                   <FlatList
                    horizontal={true}   
                    data={products}
                    keyExtractor={item => item.id}
                    renderItem={itemData => (
                                   <ProductItem
                                       image={itemData.item.id}
                                       title={itemData.item.name}
                                       price={itemData.item.price}
                                       onSelect={() => {
                                      selectItemHandler(itemData.item.id, itemData.item.title);
                                       }}
                                       >
                                      </ProductItem>
                )}
                />
          </View>

输出先显示'No Products'再显示产品，而不是先显示activity指标再显示产品

Answer 1

改变

if(isLoading){
     return <View style={{flex:1,alignItems:'center',justifyContent:'center'}}>
                <ActivityIndicator size="large" color={Colors.primary}/>
            </View>
  }

 if(!isLoading&&products.length===0)
     {
      return <View style={{flex:1,alignItems:'center',justifyContent:'center'}}>
                 <Text>No Products</Text></View>
     }

至

if(!isLoading && products.length===0){
         return <View style={{flex:1,alignItems:'center',justifyContent:'center'}}>
                    <ActivityIndicator size="large" color={Colors.primary}/>
                </View>
      }

     if(isLoading&&products.length===0)
         {
          return <View style={{flex:1,alignItems:'center',justifyContent:'center'}}>
                     <Text>No Products</Text></View>
         }

希望对您有所帮助！

如何显示 activity 指示器，直到使用 redux 从 firestore 中获取并显示在反应本机中的所有数据

How to show activity indicator until all data from firestore are fetched and displayed in react native using redux

firebase

reactjs

react-native

redux

redux-actions