I’m trying to update the notification count in my database.
I’m doing this by creating a set, which I add a UID to when I want to add to the notification count and removes a UID from the set when I want to subtract from the notification count.
I then take the size of the set and update the notification count.
the updateNotificationCount function is triggered by a lower order component.
However I can only get the database to update when isNewMatch is true. Why won’t it update the database when isNewMatch is false?
state = {notificationSet: new Set()}
updateNotificationCount = (uid, isNewMatch) => {
if (isNewMatch) {
this.setState(({ notificationSet }) => ({
notificationSet: new Set(notificationSet).add(uid)
}));
}
else {
this.setState(({ notificationSet }) => {
const newNotificationSet = new Set(notificationSet);
newNotificationSet.delete(uid);
return {
notificationSet: newNotificationSet
};
});
};
}
You don't need to do new Set() every time because you already initialize the state with new Set() so now you just do as follow:
state = {notificationSet: new Set()}
updateNotificationCount = (uid, isNewMatch) => {
let notificationSet;
if (isNewMatch) {
notificationSet=this.state.notificationSet;
notificationSet.add(uid);
this.setState({
notificationSet: notificationSet
});
} else {
notificationSet=this.state.notificationSet;
notificationSet.delete(uid);
this.setState({
notificationSet : notificationSet
});
};
}
Related
This might be a silly question, but how do I get data if I saved the state using prevState.
I am trying to retrieve data from database and send that data through navigation.
const [dataFromDatabase, setDataFromDatabase] = useState('');
const retrieveFromDatabase = () => {
db.transaction(
tx => {
tx.executeSql("SELECT * FROM PreLoveeedTable",
[],
(_, { rows }) => {
console.log("ROWS RETRIEVED");
// clear data currently stored
setDataFromDatabase('');
let entries = rows._array;
entries.forEach((entry) => {
setDataFromDatabase(prev => prev + `${entry.id}, ${entry.image}, ${entry.title}, ${entry.price}, ${entry.description}\n
});
},
(_, result) => {
console.log('SELECT failed!');
console.log(result);
}
)
}
);
}
{dataFromDatabase} will give me the whole entire data in the database.
But wanted to have each entry in the Database. For example entry for title.
I have been stuck on this for a while now and would be appreciated it if i can get a hint.
I'm trying to create an app using shopify graphql api to create an ecommerce app on react native expo.
I have an onPress that calls a setState to change the state of the graphQL variable but the results don't change from the initial state of 'currentSubCategories'
const [currentSubCategories, setSubCategories] = useState(Categories[0].subCategory[0].handle);
let {
collection,
loading,
hasMore,
refetch,
isFetchingMore,
} = useCollectionQuery(currentSubCategories, first, priceRange);
const [currentCategory, setCategory] = useState({categories: Categories[0]});
const onSubCategorySelect = (subCategory) => { setSubCategories(subCategory.handle) }
onPress={() => onSubCategorySelect(item)}
function useCollectionQuery(
collectionHandle: string,
first: number,
priceRange: [number, number],
) {
let [isInitFetching, setInitFetching] = useState<boolean>(true);
let [isReloading, setIsReloading] = useState<boolean>(true);
let [collection, setCollection] = useState<Array<Product>>([]);
let isFetchingMore = useRef<boolean>(false);
let hasMore = useRef<boolean>(true);
let defaultCurrency = useDefaultCurrency().data;
let { data, loading, refetch: refetchQuery } = useQuery<
GetCollection,
GetCollectionVariables
>(GET_COLLECTION, {
variables: {
collectionHandle,
first,
sortKey: ProductCollectionSortKeys.BEST_SELLING,
presentmentCurrencies: [defaultCurrency],
},
notifyOnNetworkStatusChange: true,
fetchPolicy: 'no-cache',
});
let getMoreUntilTarget = async (
targetAmount: number,
cursor: string | null,
handle: string,
filter: [number, number],
) => {
let result: Array<Product> = [];
let moreData: Array<Product> = [];
let { data } = await refetchQuery({
first,
collectionHandle: handle,
after: cursor,
});
...
useEffect(() => {
if (!loading) {
isFetchingMore.current = false;
}
if (isInitFetching && !!data && !!data.collectionByHandle) {
let newCollection = mapToProducts(data.collectionByHandle.products);
hasMore.current = !!data.collectionByHandle?.products.pageInfo
.hasNextPage;
setCollection(newCollection);
setIsReloading(false);
setInitFetching(false);
}
}, [loading, isInitFetching]); // eslint-disable-line react-hooks/exhaustive-deps
return {
collection,
loading: isReloading,
hasMore: hasMore.current,
isFetchingMore: isFetchingMore.current,
refetch,
};
}
I'm using flatList to show the result
<FlatList
data={collection}
renderItem={({ item }) => (
<Text>{item.title}</Text>
)}
/>
According to docs you have to pass new variables to refetch otherwise refetch will use initial values.
In this case (custom hook) you have 2 ways to solvethis problem:
return variables from your custom hook (taken from useQuery),
return some own refetch function.
1st option needs 'manual' variables updating like:
refetch( { ...variablesFromHook, collectionHandle: currentSubCategories } );
In 2nd case you can create myRefetch (and return as refetch) taking collectionHandle parameter to call refetch with updated variables - hiding 'complexity' inside your hook.
Both cases needs refetch call after updating state (setSubCategories) so you should use this refetch inside useEffect with [currentSubCategories] dependency ... or simply don't use state, call refetch directly from event handler (in onSubCategorySelect).
I'm learning vuejs and I'm doing a weather app, the goal is to rank cities with an index (humidex). I fetch weather information by API (axios) in order to collect data from several cities. I want to auto update data every x minutes, problem : some of my results are duplicated (the new data don't replace the old one).
I tried to set an unique key (based on latitude and longitude) for each item, it works for several results but not for all.
data () {
return {
items:[],
show: false,
cities: cities,
newCity:''
}
},
components: {
Item
},
computed: {
sortHumidex() {
return this.items.slice().sort((a,b) => {
return this.getHumidex(b) - this.getHumidex(a) || b.current.temp_c - a.current.temp_c
})
}
},
methods: {
addCity() {
if (this.newCity.trim().length == 0) {
return
}
this.cities.push(this.newCity)
this.newCity = ''
},
getHumidex: (el) => {
const e = 6.112 * Math.pow(10,(7.5*el.current.temp_c/(237.7+el.current.temp_c)))
*(el.current.humidity/100)
return Math.round(el.current.temp_c + 5/9 * (e-10))
},
indexGeo: (e) => {
const lat = Math.round(Math.abs(e.location.lat))
const lon = Math.round(Math.abs(e.location.lon))
return lat.toString() + lon.toString()
},
getApi: function () {
const promises = [];
this.cities.forEach(function(element){
const myUrl = apiUrl+element;
promises.push(axios.get(myUrl))
});
let self = this;
axios
.all(promises)
.then(axios.spread((...responses) => {
responses.forEach(res => self.items.push(res.data))
}))
.catch(error => console.log(error));
}
},
created() {
this.getApi()
this.show = true
}
}
The render when I update API :
By pushing to the existing array of items, you have to deal with the possibility of duplicates. This can be eliminated simply by replacing items every time the API call is made.
Replace:
responses.forEach(res => self.items.push(res.data))
with:
self.items = responses.map(res => res.data)
I followed the example from official docs, here is how to implement multiselection feature:
state = { selected: (new Map(): Map<string, boolean>) };
onPressItem = (id) => {
this.setState((state) => {
const selected = new Map(state.selected);
selected.set(id, !selected.get(id));
return { selected };
});
};
I'm struggling with making it single select though. It's easy to return new Map with false values anytime cell is tapped, but that means the cell cannot be deselected by another tap on it, which is the desired feature in my case.
onPressItem = (id) => {
this.setState((state) => {
const selected = new Map();
selected.set(id, !selected.get(id));
return { selected };
});
};
How would you implement it? Should I use lodash to iterate over the Map to find the one that already is true and change its value (now sure how to iterate over Map though), or maybe there is some better approach I am missing right now?
EDIT
Iterating over elements of the selected Map seems to be a really ugly idea, but it is simple and it actually works. Is there any better way to do it that I am missing out on?
onPressItem = (id: string) => {
this.setState((state) => {
const selected = new Map(state.selected);
selected.set(id, !selected.get(id));
for (const key of selected.keys()) {
if (key !== id) {
selected.set(key, false);
}
}
return { selected };
});
};
Thanks in advance
You can just set only one value instead of a map like this
onPressItem = (id) => {
this.setState((state) => {
const selected = selected === id ? null : id;
return { selected };
});
};
I had the same issue, my solution was:
_onPressItem = (id: string) => {
// updater functions are preferred for transactional updates
this.setState((state) => {
// copy the map rather than modifying state.
const selected = new Map(state.selected);
// save selected value
let isSelected = selected.get(id);
// reset all to false
selected.forEach((value, key) => {
selected.set(key, false);
});
// then only activate the selected
selected.set(id, !isSelected);
return { selected };
});
};
I am trying to implement an infinite scroll in React Native. Below is the source of the component:
var React = require('react-native');
var server = require('../server');
var Post = require('./Post');
var SwipeRefreshLayoutAndroid = require('./SwipeRefreshLayout');
var backEvent = null;
var lastPostId = "";
var isLoadingMore = false;
var isLoadingTop = false;
var onEndReachedActive = false;
var {
StyleSheet,
ListView,
View,
Text,
Image,
ProgressBarAndroid,
BackAndroid
} = React;
class Stream extends React.Component {
constructor(props) {
super(props);
this.ds = new ListView.DataSource({
rowHasChanged: (row1, row2) => {
console.log("rowHasChenged FIRED!!");
return false;
}
});
this.state = {
dataSource: this.ds.cloneWithRows(['loader']),
hasStream: false,
posts: []
};
}
componentDidMount() {
BackAndroid.addEventListener('hardwareBackPress', () => {
this.props.navigator.jumpBack();
return true;
}.bind(this));
server.getStream('', '', 15).then((res) => {
lastPostId = res[res.length-1].m._id;
this.setState({
posts: res,
hasStream: true,
dataSource: this.ds.cloneWithRows(res)
}, () => onEndReachedActive = true);
})
}
onRefresh() {
var posts = this.state.posts;
var firstPost = posts[0].m._id;
console.log(this.state.dataSource._rowHasChanged);
isLoadingTop = true;
server.getStream('', firstPost, 4000)
.then(res => {
console.log(posts.length);
posts = res.concat(posts);
console.log(posts.length);
this.setState({
dataSource: this.ds.cloneWithRows(posts),
posts
}, () => {
this.swipeRefreshLayout && this.swipeRefreshLayout.finishRefresh();
isLoadingTop = false;
});
}).catch((err) => {
isLoadingTop = false;
})
}
onEndReached(event) {
if(!onEndReachedActive) return;
if(this.state.loadingMore || this.state.isLoadingTop)return;
isLoadingMore = true;
var posts = this.state.posts;
server.getStream(posts[posts.length-1].m._id, '', 15)
.then(res => {
console.log('received posts');
posts = posts.concat(res);
lastPostId = posts[posts.length-1].m._id;
this.setState({
dataSource: this.ds.cloneWithRows(posts),
posts
}, ()=>isLoadingMore = false);
})
}
renderHeader() {
return (
<View style={styles.header}>
<Text style={styles.headerText}>Header</Text>
</View>
)
}
renderRow(post) {
if(post === 'loader') {
return (
<ProgressBarAndroid
styleAttr="Large"
style={styles.spinnerBottom}/>
)
}
let hasLoader = post.m._id === lastPostId;
let loader = hasLoader ?
<ProgressBarAndroid
styleAttr="Large"
style={styles.spinnerBottom}/> : null;
return (
<View>
<Post
post={post}/>
{loader}
</View>
)
}
render() {
return (
<ListView
style={styles.mainContainer}
dataSource={this.state.dataSource}
renderRow={this.renderRow.bind(this)}
onEndReached={this.onEndReached.bind(this)}
onEndReachedThreshold={1}
pageSize={15} />
);
}
}
The problem is that whenever I append (or prepend) new data, the rowHasChanged method of the DataSource doesn't fire. It just re-renders every row, even tho nothing has changed (except the new data).
Any idea why the method is bypassed?
Edit: Pass a function to setState to avoid race conditions
I just figured it out. If you are having the same issue, check the point at which you change your state with the new dataSource. Mine was like this:
this.setState({
dataSource: this.ds.cloneWithRows(posts)
});
Instead you should always use the dataSource from the previous state, like this:
this.setState(state => ({
dataSource: state.dataSource.cloneWithRows(posts)
}))
Cheers!
this worked for me, hope this helps. I created a new dataSource and assigned the updated data to it on state change as follows:`
var dataSource = new ListView.DataSource(
{rowHasChanged: (r1, r2) => ( r1 !== r2)});
this.setState({ dataSource : dataSource.cloneWithRows(posts) });
Now, the new data is assigned and the view is rendered correctly. Note that posts array that is assigned now holds the updated data. Still wondering though if it's the best way to do it but it works!
I agree it seems to make sense that you should always use the dataSource from the previous state.
Yet when I setState this way, rowHasChanged gets called for all rows, however, rowHasChanged always returns false and no rows are rendered??? Why?
// This is callback handler that the ListView DetailView will
// call when a ListView item is edited
onChange(waypoint: Object){
console.log('Callback: rowNumber= ', waypoint.rowNumber);
console.log(' length(m)= ', waypoint.distance.meters);
var itemListChanged = this.state.itemList;
itemListChanged[waypoint.rowNumber-1] = waypoint;
this.setState({
dataSource: this.state.dataSource.cloneWithRows(itemListChanged),
});
},
If I setState this way, renderRow is called for all rows unconditionally without rowHasChanged ever being called. Which is correct?
this.setState({
dataSource: ds.cloneWithRows(itemListChanged),
});
ListView, datasource, and react-native are a hard learning curve coming from C#/C/C++.
for anyone still having issue with rowHasChanged called but are still returning false the following snippets might help
the datasource is initialized like usual:
let ds = new ListView.DataSource ({
rowHasChanged: (a, b) => {
const changed = (a !== b)
return changed
}
})
this.data = []
this.state = {
listDataSource: ds.cloneWithRows(this.data)
}
here is the function which will update a row
updateRow = (row, rowId, sectionId) => {
// make a shallow clone from the stored data array
let blob = this.data.concat()
// modify the row, since we are using the triple equal operator, we need to make sure we are giving it a new object (new ref)
blob[rowId] = Object.assign({}, blob[rowId], {label: blob[rowId].label + '..cape..deh'})
// tell react to update the source
this.setState({
listDataSource: this.state.listDataSource.cloneWithRows(blob)
}, () => {
// we need to update our data storage here! after the state is changed
this.data = blob
})
}