I am building a react-native app, in which all screens share the same generic functionality like
1. Making ajax requests
2. convert snake_case keys to camelCase
3. show loading indicator while fetching data
4. subscribe to redux store and expose store as props
here are the tools I am using
react-native
expo
redux
react-redux
react-navigation
My container has no idea what urls to fetch because it is used with all the components. I am calling the container component in this way
const fetchUrls = store => return [url, url];
return MycontainerComponent(WrapperComponent)(fetchUrls);
this seems to work fine on initial load, but didn't work when visiting a screen, navigate to another and come back to the first screen again. Its as if components are cached and not recomputed again. this is for me as long as no data in the store changed. so I wrote a watcher inside the container component and to see if any value in the store changes, the component will re-render. but then this worked fine until I had one more problem.
I want to support user switch like in gmail because mine is a parent app and a parent can have 2 or more children studying at the same school and u can understand the rest.
Now when I am switching the user, I updated the redux store and I thought it would re-render stuff and it would be all fine. Until I hit with reality.
When I switch user, it seems as if the component is trying to unmount and fetch urls for new store values at the same time and react complaints with typical "don't setstate in the componentwillunmount, its a no-op, unsubscribe etc."
I have no idea what's happening, can anyone shed some light on this. Thanks.
With a stack Navigator the screens are not unmounted after they lose focus. This is a performance optimization. If you want to execute logic when a screen regains focus put your logic in NavigationEvents onWillFocus or onDidFocus.
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I am working on a React app, and within it there is a page with a lot of graphs and large list component, which takes some time to load (performance dependant). This is fine for now, but the issue comes from the following:
at the first render, there is an API call (App wide as different pages use the same data). A loading spinner shows while the API data is fetched
Once the data is fetched, it is Redux manages the state, and each component just takes what it needs from there (no more loading).
My issue is that when I navigate between pages trough links (react-router), after I click on the link it takes a while for the page to show and the menu to update the current page. None of the state data has changed in that timeframe, so I assumed a PureComponent would prevent re-render, but it doesn't work.
Is there any way to not re-render the page? I would expect to click on a link an immediately see the page that was already loaded before.
Sorry if the question is obvious, I got quite confused while researching this, with cold splitting, lazy loading, etc. which seems to be more about initial load vs. navigation?
If you have a large component dataset to mount and your state does not changes or affects re-renders you could prevent component from unmounting entirely.
If you are using react-router you can rely on setRouteLeaveHook.
If your unmount depends on conditional rendering, it is easier as you can hide your component in various way, including css display:none
There are several ways you can do this
The first one would be to not unmount the component, just hide it with CSS and display: none, but that's a shit solution if you ask me, since you'll still have the component in the DOM.
Another solution that you can use is the one that the guys from the Facebook team used when creating the official website for React. Once you hover over the link to the page, send a request to prefetch the data for that page. So, before the user even clicked, you will have the request already sent.
Another solution you can use is to cache the data. If you are not worried about users with older browsers waiting a bit for the component to load again. You can keep the data for the component in localStorage, then, when you are about to mount the component, check if the data is already in localStorage if it's there, just render the component, if not, just grab the data again.
A combination of the first and the second option would make your component pretty much always instantly render.
I'm creating a math quiz app using react-native. I wish to know how to reload all the components, upon clicking the right answer, so that a new question is loaded.
You're looking the wrong way. Reloading all the components will just render the same thing. What you are looking for is more a thing like Redux.
It will allow you to have a state container where all your data live, allowing to store the question number and update it – then components will be rendered to display the new one.
Please take a look at redux documentation, then at react-redux one.
So you would create a dispatch method, e.g. setQuestion(...), which is called when you press a button that will change the question number. The button would be a presentational component.
Then, you would have a component that wrap the whole question screen that will be updated because it was bound with redux store. It is a container component.
See more about presentational and container component here.
If you still want to refresh your app, and don't want a predictive state, you could call app.forceUpdate() where app would be instance of the top component.
I'm pretty new to React and Redux and I've been setting my environment in the past week.
I was wondering if their was such a thing as a refresh button that doesn't refresh the whole page but just the components containing the props that have changed in the store.
Example :
User_1 changes the store.
User_2 clicks a refresh button on his page (container).
The components containing props that have been modified are refreshed for User_2.
The perfect situation would be if User_2's interface components would refresh as soon as User_2 does the action, but I don't think it's possible yet. (If it is, please mention it)
Thanks in advance
UPDATE:
If you use GraphQl, it's worth looking into their "subscription" solution.
If your two user's are on different computers, then the store is not shared between them. Changes made to one user's store are not going to impact the store of a second user.
It sounds like what you really want is websockets. But this would be something you need to manage with the server-side of your application first, and which react/redux would merely consume.
In general, components will always instantly update when their props change. If a component didn't update, then it's props are still the same.
I'm fairly new to React, and I was trying to create an app that functioned thusly:
The app consists of several Pages, with multiple Components on each Page.
One of these Components is stats, which can change as the user interacts with Components on the Page.
When a user clicks on a certain Component, they will be taken to a "different" page, which is really just another Page, with different text, data, etc. This is carried out through the browserHistory.push() method. I would like to be able to carry over the changed 'stats' component from one Page to the next, but I am not sure how to do so. Furthermore, since I set the default value for stats in the Page component, it seems that any attempt at passing the changed values into the new Page would result in the new values being overridden. Can anyone help me?
Thanks.
State should live above the level of all components that need access to that state.
Remember that one of the principles of React is "one-way" data flow down the component hierarchy. Essentially, data/state should live at a high level, getting passed down to child components and consumed as needed.
In your case, you have some "stats" data that needs to be displayed across multiple Pages. So, "stats" needs to be owned by a component above all of your Page components - perhaps at the root component of the app itself. Pages themselves would just take the data in and render it, potentially with some callbacks appropriate for editing the data.
Read a bit more about Facebook's philosophy for React in "Thinking in React" in the official docs: https://facebook.github.io/react/docs/thinking-in-react.html#step-4-identify-where-your-state-should-live
One option to consider is to use React Redux to store the state of your application. You would then use mapStateToProps (See Redux API for details) to map the state into props for your stats component.
I am converting a jsp multi-page app(mpa) into a React single-page app (spa). In the mpa, the back button worked and the form retained its state.
In my new React app, the back button works but the form does not retain its state.
Question: is there a trick to make my form retain its state after "backing" to it (in an spa).
Here are the two solutions I came up with:
Encode the entire form state into the url. Then update the browser history with an updated url every time the form changes. But, this seems like a huge pain in the butt.
Modify the structure of my app such that the form in question (a React Component) stays mounted (and just use the css visibility or display property to show and hide). But, in a large app, leaving every page mounted in the DOM seems like it might lead to performance problems.
By the way, I am using popstate and the browser history api to achieve SPA behavior (i.e. i have rolled my own router) as described here.
Hopefully someone can propose a solution that is better than my two solutions. Thanks.
I ended up using something similar to Wylie Кулик's answer with a few changes:
I didn't want to switch to Redux for just this one use-case. So I used the component state of my top-level component (i.e. a component higher up the tree).
I cached the form's state on the form component's componentWillUnmount and restored the cached state on componentDidMount.
I passed the cached state as a prop from the higher component to the child component.
It ended up being a very small amount of code and is working like a charm so far.
Use Redux to have a state store which transcends any particular component. Then in your component, as part of the form submission process, dispatch an action with payload of all of the form data. This should be cached on state and then when the component is remounted by your navigation structure, it should have access to this cache via Reduxsconnectfunctions mapStateToProps method. You can repopulate your form from that.
It's not clear from your question whether or not you are submitting the form in the traditional old way. I would use e.preventDefault in the handler instead, and have all the form data on the component's state, this can be sent to Redux's state store as described above, and Ajaxed off with superagent or similar. At the same time it can be cached.
Redux: http://redux.js.org