I currently dynamically render the same component when clicking a button and the latest component is rendered on the top of the list.
Now, I want to delete the component. Each component has a cancel button to delete the rendered component. So I should be able to delete the component no matter where it is in the list.
Here's what I have so far:
local state:
state = {
formCount: 0
}
add and cancel:
onAddClicked = () => {
this.setState({formCount: this.state.formCount + 1});
}
onCancelButtonClicked = (cancelledFormKey: number) => {
const index = [...Array(this.state.formCount).keys()].indexOf(cancelledFormKey);
if (index > -1) {
const array = [...Array(this.state.formCount).keys()].splice(index, 1);
}
}
Parent component snippet:
{ [...Array(this.state.formCount).keys()].reverse().map(( i) =>
<Form key={i}
onCancelButtonClicked={() => this.onCancelButtonClicked(i)}
/>)
}
The only thing is I'm not sure how to keep track of which form was cancelled/deleted. I think I would need to create a new object in my local state to keep track but how do I know which index of the array I deleted as part of state? I'm not sure how do that? As I am using the count to make an array above.
Usually, this isn't how you'd generate a list of items. You're not storing the form data in the parent, and you're using index based keys which is a no-no when you're modifying the array. For example, I have an array of size 5 [0, 1, 2, 3, 4], when I remove something at position 2, the index of all the items after it changes causing their key to change as well, which will make react re-render them. Since you're not storying the data in the parent component, you will lose them.
Just to humor you, if we want to go with indexed based keys, we may have to maintain a list of removed indexes and filter them out. Something like this should do the trick:
state = {
formCount: 0,
deletedIndex: []
}
onCancelButtonClick = (cancelledIndex: number) => setState((prevState) => ({
deletedIndex: [...prevState.deletedIndex, cancelledIndex]
});
And your render would look like:
{
[...Array(this.state.formCount)].keys()].reverse().map((i) => (
if (deletedIndex.includes(i) {
return null;
} else {
<Form key={i} ... />
}
))
}
As a rule of thumb though, avoid having index based keys even if you don't care about performance. It'll lead to a lot of inconsistent behavior, and may also cause the UI and the state to be inconsistent. And if you absolutely want to for fun, make sure the components that are being rendered using index based keys have their data stored at the parent component level
Related
I'm updating an object within react's state which I use to display a list. The state updates correctly, however the display breaks.
This is the section of the code from inside my render function which produces the list.
this.state.shoppingItems ? this.state.shoppingItems.currentShoppingItems.map((item, index) => {
console.log(item)
return <ItemSummary key={index} onClickHandler={this.selectItem} updateShoppingItem={this.updateCurrentShoppingItem} shoppingItem={item} removeFromCurrentItems={this.removeFromCurrentItems} addToCurrentList={this.addToCurrentList} />
}) : undefined}
Here is the code that produces the previous items list:
this.state.shoppingItems ? this.state.shoppingItems.previousShoppingItems.map((item, index) => {
console.log(item)
return <ItemSummary key={index} onClickHandler={this.selectItem} updateShoppingItem={this.updateCurrentShoppingItem} shoppingItem={item} removeFromCurrentItems={this.removeFromCurrentItems} addToCurrentList={this.addToCurrentList} />
}) : undefined}
This is the method which removes the item from the current list and adds it to the previous list, where the issue occurs.
removeFromCurrentItems(shoppingItem) {
const items = this.state.shoppingItems.currentShoppingItems.filter(item => item._id !== shoppingItem._id);
let shoppingItems = this.state.shoppingItems;
shoppingItems.currentShoppingItems = items;
shoppingItem.number = 0;
shoppingItem.completed = false;
shoppingItems.previousShoppingItems.push(shoppingItem);
this.setState({
shoppingItems: shoppingItems
});
// call to API to update in database
}
Here is the list before I remove the item.
Here is the list after I remove the middle item:
Finally here is the console.log output which shows that the items have updated properly but the display hasn't updated:
I'm entirely new to react coming from angular so I have no idea if this is the correct way to do this or if there is a better way. But could somebody help me figure out why the display isn't updating?
The issue seemed to be the key on the item in the map. I replaced the index with the item's id from the database as below and now it renders properly.
return <ItemSummary key={task._id} updateShoppingItem={this.updateCurrentShoppingItem} shoppingItem={task} removeFromCurrentItems={this.removeFromCurrentItems} addToCurrentList={this.addToCurrentList} />
Similar answer here:
Change to React State doesn't update display in functional component
The issue is the update for shoppingItems. You save a reference to the current state object, mutate it, and store it back in state. Spreading this.state.shoppingItems into a new object first will create a new object reference for react to pick up the change of.
React uses shallow object comparison of previous state and prop values to next state and prop values to compute what needs to be rerendered to the DOM and screen.
removeFromCurrentItems(shoppingItem) {
const items = this.state.shoppingItems.currentShoppingItems.filter(item => item._id !== shoppingItem._id);
const shoppingItems = {...this.state.shoppingItems};
shoppingItems.currentShoppingItems = items;
shoppingItem.number = 0;
shoppingItem.completed = false;
shoppingItems.previousShoppingItems.push(shoppingItem);
this.setState({
shoppingItems: shoppingItems
});
// call to API to update in database
}
I had a similar issue with my application in which I had to delete comments made.
<textarea disabled key={note._id} className="form-control">{note.note}</textarea>
But the issue got resolved when I added the Key attribute to the list item.
this.state = {
myArray = [
{
name:"cat",
expand:false
}
]
}
clickItem(item){
item.expand = true;
this.setState({})
}
this.state.myArray.map((item) =>{
return <div onClick={()=>this.clickItem(item)}>{item.name}</div>
})
In React, i have a simple array of objects,
when i click on one of theses object, i want to change their prop and update the state, what is the proper way of doing this.
i feel like there could be a better way
You need to copy your state, update the copied state and the set the state.
this.state = {
myArray = [
{
name:"cat",
expand:false
}
]
}
clickItem(key){
let items = this.state.myArray;
items[key].expand = true;
this.setState({items})
}
this.state.myArray.map((key, item) =>{
return <div onClick={()=>this.clickItem(key)}>{item.name}</div>
})
Okay, a couple of things.
You're mutating the state directly which is going to fail silently and you're also missing the key prop on your <div.
This is easily resolved though by using the data you have available to you. I don't know whether each name is unique but you can use that as your key. This helps React decide which DOM elements to actually update when state changes.
To update your item in state, you need a way to find it within the state originally, so if name is unique, you can use Array.prototype.find to update it.
clickItem(item) {
const targetIndex = this.state.items.find(stateItem => stateItem.name === item.name)
if (targetIndex === -1)
// Handle not finding the element
const target = this.state.items[targetIndex]
target.expand = !target.expand // Toggle instead of setting so double clicking works as expected.
this.setState({
items: this.state.items.splice(targetIndex, 1, target) // This replaces 1 item in the target array with the new one.
})
}
This will update state and re-render your app. The code is untested but it should work.
I have a React Native form that allows me to add an Input UI in the form, by clicking a button with this function. This allow me to generate it on the fly. The code for that is this.
addClick() {
this.setState(prevState => ({ values: [...prevState.values, ""] }));
console.log(this.values[0].name);
}
That part works well, but I'm having a problem extracting the data from the dynamic inputs, and add it to an array. So far I have tried this
setVal = value => {
const values = this.state.values[0];
if (values[0].name === "" || values[0].description === "") return;
[...this.state.values, value];
this.setState(values);
console.log(values);
};
How do I organize my states properly so that I can add as many inputs I need, and when I'm finished, I can update the state, and access the new data in my list component?
How do I update my state to the new Array? at the moment, this.state only shows the initial state set at the top.
I'm missing a few things
Please take a look at the full code sandbox HERE so you can see:
See...your created isssue is not so obvious we need to see where you call setVal() function but....
i think you will be more comfortable if you render your <input/> s directly from your state array, not from const x = [] variant. because it seems like you want a dynamic view and in such a cases you will need to bind your loop quantity from state. so:
this.state = {
x: [0,1,2,3,4]
}
and inside your render :
{this.state.x.map(x => {
return (
<TextInput
placeholder={`name${x}`}
value={values[x.toString()]}
handleBlur={() => handleBlur(x.toString())}
onChangeText={handleChange(x.toString())}
style={styles.input}
/>
);
})}
Situation 1 - I check my individual checkboxes, my header checkbox gets checked. This is method 1 and works fine.
Code for same
index.vue
<VCheckbox
checked={this.checkSelections[idx]}
nativeOnChange={e => {
this.$set(this.checkSelections, idx, e.target.checked);
let allSelected = true;
for (let i = 0; i < this.checkSelections.length; i++) {
allSelected = this.checkSelections[i];
if (!allSelected) break;
}
this.$root.$emit("checkmarkHead", { allSelected });
}}
/>
Head.vue
mounted() {
this.$nextTick(() => {
this.$root.$on("checkmarkHead", ({ allSelected }) => {
console.log("checkmarkHead", allSelected);
this.allSelected = allSelected;
});
}
},
Situation 2 -
I check my header checkbox and all my checkboxes are checked. Vice-versa is true as well. So method 2 corresponding to this works fine too.
Code for same -
Head.vue
<HeadItem>
<VCheckbox
checked={this.allSelected}
nativeOnChange={e => {
this.allSelected = e.target.checked;
this.$root.$emit("selectAll", {
allSelected: this.allSelected
});
}}
/>
</HeadItem>
index.vue
mounted() {
this.$nextTick(() => {
this.$root.$on("selectAll", ({ allSelected }) => {
this.checkSelections = Array(this.sortedData.length).fill(allSelected);
});
});
}
Problem - When I do situation 2 after Situation 1, the same methods don't work as expected. The view isn't updated. Similarly, executing Situation 1 after Situation 2 won't work either.
Here's the link to
Code Link - https://codesandbox.io/s/vmwy3v4203
I'm clueless now after handling all mutations caveats etc.
I owe you an apology. This is indeed another reactivity issue which could be solved by providing a key attribute ..
The key special attribute is primarily used as a hint for Vue’s
virtual DOM algorithm to identify VNodes when diffing the new list of
nodes against the old list. Without keys, Vue uses an algorithm that
minimizes element movement and tries to patch/reuse elements of the
same type in-place as much as possible. With keys, it will reorder
elements based on the order change of keys, and elements with keys
that are no longer present will always be removed/destroyed.
You can assign a unique key value to an element, which if changed will force Vue to re-render that element. In your case you can assign keys to your VCheckbox elements equal to their checked value, forcing Vue to re-render them when they're checked/unchecked. For example ..
<HeadItem>
<VCheckbox
key={this.allSelected}
checked={this.allSelected}
nativeOnChange={e => {
this.$emit('change', !this.allSelected)
}}
/>
</HeadItem>
I've taken the liberty to re-write your allSelected property as a computed property and removed the event listener you set up on the root instance. I think it's much cleaner this way ..
Assume I have the next piece of code inside the React component
removeItem = (item) => {
this.items.remove(item) // this.items -> mobx array
}
renderItem = (item, index) => {
var _item = undefined
switch (item.type) {
case "header":
_item = <Header key={item.id} onRemove={() => this.removeItem(item)} />
// a few more cases
// note that item.id is unique and static
}
// return _item -> works fine
return [
_item,
this.state.suggested
? <Placeholder key={-item.id} />
: null
]
}
render() {
return (
<div>
{this.items.map((item, i) => renderItem(item))}
</div>
)
}
Also assume that inside each of item I have a button that triggers onRemove handler with click. And each component has textarea where user can enter his text.
Obviously, when user enters text inside item's textarea, it should be saved until item will be removed.
The problem is when I remove some item, each item that goes after the removed one is being remounted (edited for Vlad Zhukov). It happens only when I return an array from renderItem(...) (I mean, when I return only item, this problem doesn't happen).
My question: is this a bug, or it's a feature? And how can I avoid it (desirable without wrapping item and Placeholder with another React child)?
UPDATED
I tried rewrite renderItem(...) the next way:
renderItem = (item, index) => {
var Item = undefined
switch (item.type) {
case "header":
Item = Header
// a few more cases
// note that item.id is unique and static
}
// return _item -> works fine
return [
<Item key={item.id} onRemove={() => this.removeItem(item)} />,
this.state.suggested
? <Placeholder key={-item.id} />
: null
]
}
And it still causes the problem.
Rerendering is absolutely fine in React and can be considered the main feature. What happens in your case is components remount when you make changes to an array of elements when these elements have no key props.
Have a look at this simple example. As you can see rerendering components has no difference but removing the first element will clear values of inputs below.
You've got 2 options:
Use a component instead of an array and set key to it (see an example). There is really no reason not to.
Remove all keys. The reason why it works is because React internally already uses keys for elements. However I wouldn't suggest this as it doesn't look reliable enough to me, I'd prefer to control it explicitly.