i currently have an object and inside this object i have multiple objects and Arrays. I want replace an Array inside this object with a new Array, so i thought of making a copy of the entire object and simple replace the Array i wan to change with the updated Array. My problem is i couldnt complete my code, i have the idea of how to do it but cant execute it.
setListings(listings=>
listings.map(item =>{
if(item.id === msg.id){
//console.log(item)
//console.log(item.Message)
const newMessages = [msg,...item.Messages]
//console.log(newMessages)
return console.log([msg,...item.Messages],{...item}) // just for testing purpose i
am returning a console log
to see what it will get me. Not correct.
}
return item;
})
);
So basically listings is my state variable, here console.log(item) prints out the entire object, console.log(item.Messages) prints out the current Messages Array which i want to replace, console.log(newMessages) prints out the new Messages Array which i want to replace the current Messages array with.
cartItem.map((food,index)=> {
if(food.food_id == newFoodItem.food_id && food.id == newFoodItem.id){
const AllFoodData = cartItem
AllFoodData[index] = newFoodItem
AsyncStorage.setItem('#Add_cart_Item', JSON.stringify(AllFoodData))
.then(() => {})
.catch(err => console.log(err))
ToastAndroid.showWithGravityAndOffset('Cart Replace Successfully',ToastAndroid.LONG,ToastAndroid.BOTTOM,25,50 )
}
})
So basically what i want to achieve here is to add the msg object to the existing Messages Array.
Since lsitings is an Array of objects using the .map i can spread through each object and check if the id of that object is each to my msg.id. if that is true then i want to return a copy the that specific listing and edit the Messages Array within [msg, ...item.Messages] otherwise return the existing item.
setListings(listings=> listings.map(item => {
if(item.id === msg.id) {
return {
...item,
Messages: [msg, ...item.Messages]
}
}
return item;
}));
});
Related
After executing the newData[0].id = newValue I am actually updating the react initialData state. How is that possible?
Is my understanding that filter should return a new array different than the original one, also I am not ussing the setState feature so I don't understand why the state is changing.
Because arrays are mutable. it will keep the reference to the original array even after filtering.
use the spread operator to avoid mutating the original array
const data = [...newData]
data[0].id = newValue
As per the new beta docs on updating items in array
setInitialData(prev => {
// create a new array
const withReplaced = prev.map(elem => {
if (elem.id === id) {
const newVal = //set new value
// create a new updated element
return {
...elem,
id: newVal
}
} else {
// The rest haven't changed
return elem;
}
});
return withReplaced;
})
Hope it helps
you can't update the initialData,but the you can update the son of the array.And if you don't use "setData".The views won't change.
setListOfPosts(curPosts => {
let newPosts = [...curPosts];
newPosts[newPosts.findIndex(p => p.id === postId)].alert = response.data;
}
});
//is curPosts an instance of array or complete array?? my listofPosts is an array of objects
Your setState call needs to return newPosts, and you're creating an array using the spread operator which is why it's coming back as an array of objects.
I'm not sure what your desired output is, but by adding a return function it will set the state:
setListOfPosts(curPosts => {
let newPosts = [...curPosts];
newPosts[newPosts.findIndex(p => p.id === postId)].alert = response.data;
return newPosts
}
});
This is untested but if your logic is correct should return an array of objects with the objects alert value updated.
Another option would be to do your logic before your setState call, by creating a a newState array and then simply updating the state with that new array without the use of the callback.
The callback function is useful if you want to add a new object to state array or do something that preserves the initial state, in your example you could do it without the callback like this:
// Create a copy of the state array that you can manipulate
const newPosts = [...newPosts]
if (data.response) {
// Add your logic to the state copy
newPosts[newPosts.findIndex(p => p.id === postId)].alert = response.data;
// Replace state with state copy
setListOfPosts(newPosts)
}
Again untested but hopefully this should help you understand the use of the callback function and the right way to use it.
My issue is that when i call the function getAllFlashCardsFromQuest(), its call all flash cards ever created in all the pages, i wanna only the objects that comes from a specific pathname, or a way to filter the cards array.
async function getCards() {
let cardsValues = await getAllFlashCardsFromQuest() as FlashCard[]
let cardsFiltered = cardsValues.filter(()=>{
return history.location.pathname === 'CriarAlternativaQuest'
})
console.log(cardsFiltered)
setCards(cardsFiltered)
}
the object look like this:
There's not much context with your code, so I can only help so much, but one thing's for sure, and that is history.location.pathname isn't changing and you're comparing it with another constant. So cardsFiltered will be either a list of true or a list of false.
Whenever you're filtering a list, you need to take each item or a property of each item and use that in your comparison.
Ex.
async function getCards() {
let cardsValues = await getAllFlashCardsFromQuest() as FlashCard[]
let cardsFiltered = cardsValues.filter((cardValueItem) => {
return cardValueItem.pathname === 'CriarAlternativaQuest'
})
}
The thing is that you need to figure out what value or property inside of your cardsValues list that you need to compare it with 'CriarAlternativaQuest'
I have two collections: users_unprocessed and users_processed. When a user is new, he will be added to the users_unprocessed collection. If he is processed, he will be deleted and added to the users_processed.
I want to create a list with all users. Therefore I need to find a user in users_processed or users_unprocessed. The list should be reactively and show live updates, therefor I need to use .onSnapshot().
database.collection("users_unprocessed").doc(id).onSnapshot((snapshot) => {
if (snapshot.numChildren > 0) {
setFetchedUser(snapshot.data());
} else {
database.collection('users_unprocessed').doc(id).onSnapshot((snap) => {
if (snapshot.numChildren > 0) {
assignUser(snap)
} else {
// Error Handling
}
})
}
This code is not giving my any result no matter of the doc exists in the users_unprocessed or users_processed.
If both collections are correctly set you just need to use the forEach function on each of them and put them on an array or list or whatever you want. Something like that:
const allUsers = [];
database.collection("users_unprocessed").onSnapshot((querySnapshot) => {
querySnapshot.forEach((doc) => {
allUsers.push(doc.data().name);
});
});
And then you can do the same with the other collection in the same list. If you don't want to put them on an Array but you have any other method or function you just need to change the last part.
createNewList = (id, input) => {
const foundCard = {...this.state.cards.find(card => id === card.id)};
this.setState(foundCard.list = [...foundCard.list, input]);
};
Hello everyone
There is an array of data (list), which is stored in the state for each object (card).
Problem: I can’t seem to add a new element to this array.
The way it is set up creates only one element and change it every time. But I need to create a new one every time. I tried to create a separate array, add to it using newArray.push (input) and then do this.setState (foundCard.list = [... foundCard.list, ... newArray])`, but have the same result.
I don’t use Redux, because I just started to learn React and I store everything in state yet.
Thanks in advance for your reply.
createNewList = (id, input) => {
const newCards = this.state.cards.map(card => {
if (card.id === id) card.list = [...card.list, input];
return card;
});
this.setState({
cards: newCards
});
};