componentWillMount is deprecated and will be removed in the next major version 0.54.0 in React Native

Question

I use the react native latest version of 0.54.0 and Whenever run the apps on iOS there is found warning about deprecate the lifecycle methods. and also please update the com

Answer 1

You should move all the code from the componentWillMount to the constructor or componentDidMount.

componentWillMount() is invoked just before mounting occurs. It is called before render(), therefore calling setState() synchronously in this method will not trigger an extra rendering. Generally, we recommend using the constructor() instead. Avoid introducing any side-effects or subscriptions in this method. For those use cases, use componentDidMount() instead. This is the only lifecycle hook called on server rendering.

componentDidMount() is invoked immediately after a component is mounted. Initialization that requires DOM nodes should go here. If you need to load data from a remote endpoint, this is a good place to instantiate the network request. This method is a good place to set up any subscriptions. If you do that, don’t forget to unsubscribe in componentWillUnmount(). Calling setState() in this method will trigger an extra rendering, but it will happen before the browser updates the screen. This guarantees that even though the render() will be called twice in this case, the user won’t see the intermediate state. Use this pattern with caution because it often causes performance issues. It can, however, be necessary for cases like modals and tooltips when you need to measure a DOM node before rendering something that depends on its size or position.

From the official docs

Answer 2

componentDidMount isn't deprecated and is definitely still safe to use, so there's no need to add UNSAFE_ to that method. The componentWillSomething methods are the ones that seem to be on their way out. Instead of componentWillMount, use a constructor for the stuff that doesn't produce side-effects, and use componentDidMount for the stuff that does.

Answer 3

You should avoid using componentWillSomething in order to use constructor or componentDidMount

However, You have to be very carefully which one you'll use. A typical scenario is when you want to display a loading (using states) immediately after you open a screen

this.setState({ isLoading: true });
...
this.setState({ isLoading: false});

In this kind of case you have to use componentDidMount in order to set states. This is what React said about constructors

Typically, in React constructors are only used for two purposes:

1. Initializing local state by assigning an object to this.state.

2. Binding event handler methods to an instance.

You should not call setState() in the constructor(). Instead, if your component needs to use localstate, assign the initial state to this.state directly in the constructor.

Good coding!