here is my problem.
I am using react-window to render large tables. Each row has its own local state. After I delete a row, the next row moves up and gains the state of the deleted row (this how it looks in my app).
Is there a workaround for this problem? Can i have local state for each row with react-window?
codesandbox example | gif how it works
There is a fundamental issue here - react-window will dynamically render, unmount and rerender components. So if you want data persisted across re-renders - you must pass the count via props and a function to change it. Store the data with the item data itself.
I will try and show a working demo of that soon ,but look at this to understand yet another problem happening with this code: https://codesandbox.io/s/react-window-row-state-problem-mmukt
I have edited the size to be 150 instead of 50, this leads to the window getting a scrollbar. Now, try and click on "two" multiple times. This will increase the count. Next, scroll to bottom and go back up. You'll see that the count is lost.
This is because of the way react-window mounts and unmounts components.
To fix this in your original code, I made the following modifications:
1. Move count/active state to parent.
2. Pass the updateCount function to TableRow.
Essentially, the TableRow is now a pure component :)
Here is the link: https://codesandbox.io/s/react-window-row-state-problem-uzsdl
Hope this helps.
In a nutshell, you can't. The issue is that, when you delete an item, the same component that was used previously for it will be used to render the item after it (so if you delete the 2nd item, the 3rd item will use the Row from the old 2nd element). It will maintain that item's state. If you add a useEffect to detect that the item changed, then you break everything after it (since everything is bumped up one, all of the items after the deleted item will reset their state. You don't have access to the sibling component's state, so you have no way to propagate the state.
You have a few options here:
Add the selection to the properties of the item, and provide a way to update the item.
Make the selection state part of the App component's state, and pass it down to the component so it can render appropriately.
I'll also add that you probably don't want to map over your presumably large list of items every render like you are now. It looks like you are doing this to expose deleteItems. I would recommend something more like this:
<FixedSizeList
height={500}
width={300}
itemCount={items.length}
itemSize={50}
itemData={{items, deleteItem}}
>
{Row}
</FixedSizeList>
Then your Row component's data will have both the items array and the deleteItem function. If you maintain your selected rows state in App, you easily extend this to pass the selected state and modification functions down to your Row component.
Related
I want to build a simple app like in picture attached with react js, I just cannot find the right idea of:
How to "select" photos(or item) in an application and have the "cart"-like component appear at the bottom when at least one photo/item is selected(and close and deselect all already selected photo/items) and expand the cart-like component at the bottom when clicked to show what's been already selected.
What is the best approach to this?
P.S I'm new to react with a big idea in mind xD
app's view
This question definitely needs more information, but I will try to point you in the right direction. There are hundred of ways to create the UI/functionality you are describing but here is a very generic overview;
The "items" (Img1-6) looks like a grid of ShopItem components, possibly in a CSS Grid / flexbox. Each ShopItem would probably make use of an onClick method to "do something" when it is clicked - this may involve updating a state (using the useState react hook) somewhere which tells you if a ShopItem is checked or not. It could also potentially use a callback method to do something in the parent when the items are checked.
I imagine that each ShopItem may own its own "checked" state or may update a global state (Such as Zustand or Redux) or a Context (React) when it is toggled on and off. The checked state of a ShopItem would also inform the UI of the component.
The "cart-like" component could be looking at the global state/context/callback from the item component, and could change based on its value and how many checked items there are. (Eg/ checkedItems !== 0 ? show : don't show)
This is just one way in which this UI can be built, if you would like a more specific solution, please edit your question to include code snippets and what you've already tried.
I have adapted this example from the material-ui table component example from the docs. In the provided example, rows can be selected, in which case the checkbox for that row will be checked. The problem with the example implementation is that when a change is made to any row, all of the rows will be re-rendered, even though only one of them has changed. This works fine as long as the number of rows is quite small but quickly degrades when rendering more rows.
As an attempted fix for this, I tried to implement shouldComponentUpdate in my Row components, to check if the row data (via the 'name' property), or the isItemSelected prop has changed (I ignored the other props as the callback function props will always be considered to have changed on each render). For some reason, this totally breaks my selected state in the parent Table component.
Here is my example, highlighting the issue: table-bug-example. As is, this reflects the example provided in the docs. You can see the lag issues if you set the rows per page drop down to a higher number. You can uncomment my shouldComponentUpdate implementation in the Row Component, to see how the state breaks in the Table component, when using shouldComponentUpdate in the children.
Expected Flow:
parent state keeps track of selected rows
clicking on row updates parent state
parent passes isSelected prop to child rows
row component checks to see if isSelected has changed, and re-renders only if this prop has changed
I have been struggling with this for several hours and can't for the life of me figure out what is wrong. I've also tried using React.memo, as well as different implementations of the setSelected state in the table component (I was previously using a dictionary to keep track of the selected rows, but for now I've left the default implementation provided in the material-ui docs, to minimize any issues introduced in my code).
Might anyone happen to know what is going on here?
When you used your custom shouldComponentUpdate what happened you "saved" the old version of handleClick inside of your custom MyRow, and since handleClick is not a pure function(it is using previous selection to determine prev selection state) it was always reading the wrong state.
For example you have 2 rows (row1 and row2). On initial render selection is : [], and the both render with the version of handleClick that has captured selection as []. You click on row1, it will rerender since its isItemSelected prop has changed, but row2 will not since your shouldComponentUpdate returned false. That means when you click on row2 it will use the handleClick from the first render wich had the selection as [] and it will uncheck row1 selection. There is no magic mechanism that binds selection, it all uses javascript context capturing.
Thats why custom shouldComponent is very dangerous. I would recommend using MyRow as a PureComponent (no need to use React.memo, you can just extend PureComponent) and transform handleClick inside table so it doesnt change (doesnt depend on current selection). Something like this: https://codesandbox.io/embed/material-demo-i0yp2?fontsize=14&hidenavigation=1&theme=dark
Hope this helps.
I've got an app that shows a list of items in a grid. Some of the items have an embedded video which flashes or stops playing (if it's already playing) when it's rerendered.
The list is maintained in Redux. When the user scrolls to the bottom of the page it loads more results which causes the Redux state to update which, in turn, causes the grid to rerender all of the items plus the new items.
I'm looking for a solution that will just add more items to the end of the grid instead of rerendering everything.
I've got a component that holds the entire grid. It renders a component for each item in the grid. In each item I have a component that holds the embedded video.
Any ideas?
If each item in the grid is a component, like you said, you should use React.memo (for functional compoents) or Reat.PureComponent (for class components). It will prevent the component from rerendering if the props have not changed. I can't guarantee your videos will keep playing, but if the only reason they stop playing or flash is because the component is being rerendered then it should fix the problem.
Maybe this can help: when passing information from redux to your component, try to update the list of the objects instead of sending a new one
It's redux UpdateObject method.
I have dropdown list with a lot of checkboxes, so this container has scroll. But when i click on any checkbox - it selects\deselects itself and then state changes.
So the problem is that after rerendering this container is back to the top. Is it possible to keep container's scroll after rendering without saving it to the state?
You can save the "snapshot" of the scroll position before the commit phase.
getSnapshotBeforeUpdate() shows kind of what you are looking for.
The documentation example saves the current scroll position within getSnapshotBeforeUpdate lifecycle method and then use the snapshot value passed to componentDidUpdate(prevProps, prevState, snapshot) as the last argument to restore the scroll position.
It doesn't require creating a state to save the scroll position as you requested.
It's happening because you are re-rendering the complete list of the checkboxes.
There are 2 possible approaches:
Re-render only relevant checkbox
Save the scroll position of the container and update it once component is re-rendered.
Unfortunately, you haven't added any code examples, so can't share the code changes.
With react-virtualized, when you scroll the list and set the same scrollToIndex, it doesn't scroll back to the same index.
Is there a way to reset the list back to the position?
That's because the prop hasn't changed. You can use the scrollToCell or scrollToRow method (depending on whether you're using Grid or List/Table) to re-scroll to the same index.
As #brianvaughn also said, you List doesn't scroll to the index back again because to the props to the react-virtualized list component haven't changed.
Since, By default all react-virtualized components use shallowCompare to avoid re-rendering unless props or state has changed. The components won't re-render until an update has happened.
The solution to this is to let react-virtualized know that something external has changed. This can be done a couple of different ways.
Also its mentioned in the documentation that you have two ways to let react-virtualized know that something has changed
Pass-thru props
The shallowCompare method will detect changes to any props, even if they aren't declared as propTypes. This means you can also pass through additional properties that affect cell rendering to ensure changes are detected. So you could pass additional props that change when you fire an event that for the virtualized list doesn't change anything.
<List
{...listProps}
sortBy={sortBy}
/>
Public methods
Grid and Collection components can be forcefully re-rendered using forceUpdate. For Table and List, you'll need to call forceUpdateGrid to ensure that the inner Grid is also updated.
So whenever you wish to update the scrollToIndex if, its value hasn't changed from the previous value you could call forceUpdateGrid on the List. This method can come in handy in a lot of other situations as well
Having said that, it may not be the best option always as there is another option to force scroll event if the scrollToIndex hasn't changed, which is the scrollToRow option. However it requires the row you want to scroll to be visible. Its its not, you won't be able to use it.
scrollToRow (index: number)
Ensure row is visible. This method can be used to safely scroll back
to a cell that a user has scrolled away from even if it was previously
scrolled to.