how can I make a component to force update its sibling. Currently my component rerenders on componentDidMount but this happens on a selection from a drop down.
Thanks
If you're incurred in this type of problem I suppose you do not use Redux or similar. The easiest way is to lift the state to the common parent component:
Doc ref: https://reactjs.org/docs/lifting-state-up.html
If Comp1 and Comp2 are siblings and Parent is the common parent for the two siblings
You can pass a callback function from Parent to Comp1, whenever Comp1 is updated it can notify the Parent via the callback prop.
In parent you can listen to props change using componentwillreceiveprops and re render the Comp2 using the changed props again passed to it from the Parent.
or in a more complicated appliation set up, you can use redux to store into a global state.
Related
In order to update a prop inside a child component, I was passing a function that updates this prop as a prop to the child component. So the question is that a good approach? and
what is the best approach to update a prop from a child component when using Typescript ?
this is called lifting state up and it is a common approach in React to keep components in sync,
it works by moving the state to the parent component (so you can share it with other siblings) and then passing the state and the event handler as a props
for more details see the official react docs
https://reactjs.org/docs/lifting-state-up.html
In the React docs, it says
By default, when your component’s state or props change, your component will re-render.
I understand for state changes, but I am not sure about when props change. As far as I am aware, props are always passed from the parent component to the child component. And when the parent component re-renders (due to a state change, for example), all child components also re-render (ignoring shouldComponentUpdate). So it seems to me that if the parent component re-renders, all child components will re-render regardless of whether I am passing new props to them or not. If I do pass new props to the child component, the fact the child re-renders is simply because the parent is re-rendering, not because I am passing new props.
Is there a scenario where a parent component passes new props to a child component, causing the child component to re-render, but it is not caused simply by the parent component re-rendering?
Is it possible to see an example where a component will re-render because it receives new props, rather than because the parent is re-rendering (or its own state changed)?
Sorry if this is a basic question, I am new to React.
EDIT: I see that Redux can cause components to re-render by passing new props, I'm curious to know what Redux is doing behind the scenes to achieve this.
To answer the question you ask at the end:
If the child is a PureComponent or wrapped in React.memo it will only re-render if the props change. If the parent re-renders then the component will compare the props it receives and if they're identical to the previously passed props it will not re-render.
If the child is not a PureComponent or wrapped in React.memo then it will re-render any time its parent re-renders.
I‘m not new to react and was asking the same thing. There was an article which made it clear for me: https://thoughtbot.com/blog/react-rendering-misconception
The re-render is needed for diff-checking if DOM updates are necessary. If you‘ve implemented shouldComponentUpdate or wrapped with memo (both returning false), then rerender is skipped.
If a child component is connected using redux or context, then it might rerender even without parent being rerendered.
When you use provider, or HOC, or Redux with mapStateToProps for example, the props are changed from other component injecting props.
Connect middleware of redux is similar to subscription, each child component can directly connect to the store through subscription, and whenever the store changes, the store tries to resync all its connected components. New incoming data to any component comes as props resulting in re-render.
Any component getting changed from outside of its state can be through props only, so it is similar to a parent component passing new data / redux store pushing new data to the component.
I have never used mobx before so my understanding could be off. I have a parent component and child component both injected and observing the same store. The store is passed to props on both when components are initialized. The child component is the one triggering the store action and it accurately updates the ui with the change, however the parent component is simply referencing the same observed property from the same store and does not update or re-render when the child component updates the store. I would think that since the parent component is observing the same observed property that it should receive the updated value, but it's not.
Yes you can inject store to any Component but you should Change mobx observable in Parent Component ,then mobx will trigger re-render and let both parent and child knows that the state has benn changed.you should use #observer on both component by the way.
I was going through a code and found that
this.props.formVisibility = false
As one cannot update the properties in react's component, the code shouldnt have work but the execution went without any errors.
Now I am wondering, On what conditions one is able to edit props in the component?
Suppose you have parent - child relationship. where parent's state pass as props to child component then whenever you want to update props you need to update parents state not props in child component. once state get updated this will update to props as well in child component hope so it clear the point
refer : https://gist.github.com/sebkouba/a5ac75153ef8d8827b98
I was wondering if a connect()ed sub-component will re-render if its parent returns false in shouldComponentUpdate?
Say, we have a component tree looking like this
connect(Foo extends PureComponent)
DumbBar
connect(Baz extends PureComponent)
So neither Baz, nor Foo, should re-render if their own props, supplied to them by mapStateToProps, keeps the same. But what happens if the state of the redux store changes and the connect()ed Baz component is notified of a state change and is supplied with new props? Will it re-render, or will the hierarchical update model of React prevent anything from rendering?
Or is this whole question perhaps a bit off, since it's not possible for a child components new rendering to take effect without affecting the ancestors - forcing the ancestors to re-render if a child changes?
If the last point is true, then putting a connect-ed component as a child of a PureComponent is lethal, as it breaks all optimizations you thought were in place, causing re-renders in other places in the sub-tree of the parent.
Yes, it will re-render.
That's the whole idea of using connect - you don't have to pass the props and you can embed it anywhere - it will take care of keeping your component up-to-date.
Each component built with connect will wire up it's own subscription to be notified of changes to the redux store.
So if only the props supplied to mapStateToProps for the child component have changed then the child component will re-render whereas the parent component will not.
You can see this yourself by adding a simple console.log to the render function.