Currently, I read some state from AsyncStorage in componentWillMount. However, some screens modify what is in AsyncStorage, and it does not appear that componentWillMount is called when returning (this.props.navigation.goBack()) to a screen, so they don't receive the update.
What, if anything, is called? What are the component lifecyle functions that are called on the return to a screen? Are any of these only called once, when the screen is to be shown again?
componentDidFocus is currently in design not avaiable yet, see react-native open issue #51.
Try this alternative way react-navigation-addons.
Related
I have put console log inside of my functional component file. In this file render whenever the API called. If I called API in some other file and the API not related to that file still got logs. I am not sure why. I have checked useEffect and usestate but no clue. Even search from google no clue.
I am using Usestate to store and useEffect to reloaded the the page when data change
I am using apisauce to call the API
React native navigation bottomtab to navigate the screen
Using React.memo but still page rendered.
Any one please help me to resolve this issue. because I am new to react native.
React components automatically re-render whenever there is a change in their state or props. A simple update of the state, from anywhere in the code, causes all the User Interface (UI) elements to be re-rendered automatically.
However, there may be cases where the render() method depends on some other data. After the initial mounting of components, a re-render will occur when:
A component’s setState() method is called.
A component’s forceUpdate() method is called.
Warning: You should normally try to avoid all uses of forceUpdate() and only read from this.props and this.state in render().
So in my app I have a main component which have switch navigator and then inside switch navigator I have a tab navigator which renders different screens. I have registered notification handler in top component.
Now the problem is that when notification is received, I want to make some changes on screens inside tab navigator.
I have read about redux which will provide common store so state could be updated but I dont want to use that.
I have also read about lifting state up but in my case i have more nested components so I dont want to do that as well.
So suggest me some way to do it?
I have solved the problem by using react context api. It is simple wrap your top level component with provider and define some veriable and access that variable in any component.
I have a component that is sometimes pushed as a regular screen on top of the stack, and sometimes shown as a modal.
When a specific event occurs, I need to get rid of the component. But I don't know if it's a modal or a regular screen, so I don't know if I need to call Navigation.pop(componentId) or Navigation.dismissModal(componentId). Is there a way to check before calling?
I tried just calling both in succession, but then one of them fails and throws an error.
I could wrap them both in a try/catch, but that seems like an anti-pattern. What is the recommended way to deal with this?
You can use a command listener and track when it's pushed or shown as a modal
I have a sort of WhatsApp clone project. From the users listing component, it will redirect to each users chatWindow. I dont want to re-render the chatWindow component which was already rendered.
This is what happening
Navigate to ChatWindow1 from Userchannel - ChatWindow1 mounted
Navigate to Userchannel from ChatWindow1 - ChatWindow1 unmounted
Navigate to ChatWindow2 from Userchannel - ChatWindow2 mounted
Navigate to Userchannel from ChatWindow2 - ChatWindow2 unmounted
Navigate to ChatWindow1 from Userchannel - ChatWindow1 mounted again.
I know using state we can render the ChatWindow again. But Is there a possibility to avoid the unwanted re-renderng. Currently I am usinf RNRF as the router.
Optimising re-render can be done in multiple ways in react.
You can use PureComponent Implementation where react itself shallow compares the props and re-renders only when necessary.
If you want more granular control, go with shouldComponentUpdate which gives you a lifecycle method where you can compare the props and decide whether you want to avoid render. Please make sure the comparison is not complex. The more complex comparisons can make the app slow, in which case the optimisation back fires.
Use Flat list instead of List view or scrollview for better performance and make sure you add a keyExtractor and Item as a PureComponent.
Make sure the code splitting is properly done. you cannot optimise a very large amount code in a single page. If the components are small enough, you can optimise them better.
If you have a lot going on the JS, I would strongly recommend using a native navigation solution like react-native navigation
You can use console logs in render to find out the render count and take necessary actions. Please make sure that these optimisations can block necessary renders as well. So make sure props are different when you want to re-render things.
Regarding the mount / unmount
In most cases the navigation keeps the screens in the stack. Going back will not trigger a re-render. You can do one thing, make sure page works on props, so that re-render happens only when data changes.
Helpful Links:
https://medium.com/#ohansemmanuel/how-to-eliminate-react-performance-issues-a16a250c0f27
https://medium.com/vena-engineering/optimizing-react-rendering-61a10e741edb
Since your screens are unmounted there is nothing wrong to re-render when you navigate back to that screen. Of course you could avoid this by having all your screens mounted but that might cause memory leak.
i am stuck in a problem that is,
in my application one screen has a Tabbar component so i have used Tabnavigation from react-navigation.
so there is two tabs in that screen and both of that tabs have GET API for displaying data
so my main problem is when tab screen is open at that time both tabs file is calling API because of tabnavigator is in stack navigator.
So please help me to solve this issue.
i have to do like this::-
when i click on tab then after API will be call but here when the screen is arrive at that time both tabs call their API.
so please sort out this issue guys.
You can use TabNavigator's lazy prop.
lazy - Whether to lazily render tabs as needed as opposed to rendering them upfront.
This way your API call will happen only when you switch to that tab. The call will happen only on first switch though. You may need to add some logic to recall API on certain event or time to get the new data.