react-navigation: Detect when screen, tabbar is ac

问题:

Perviously when I wanted to make some actions when screen is opened I put them inside componentDidMount. For example I can fetch some data.

like this.

componentDidMount() {
  this.updateData();
}

But with react-navigation componentDidMount occurs only one time when user open screen first time, and if later user open this page again it will not trigger componentDidMount.

What is proper way to detect when page(screen) is activated and do actions?

回答1:

With react-navigation, you can do that.

1. Add listeners in componentDidMountor componentWillMount

   this.subs = [
     this.props.navigation.addListener('didFocus', (payload) => this.componentDidFocus(payload)),
   ]; 
   

   or

   this.subs = [
     this.props.navigation.addListener('didFocus', this.componentDidFocus),
     this.props.navigation.addListener('willBlur', this.componentWillBlur),
   ];
   

   Then you can do anything in componentDidFocus, like fetching data, updating data,...

2. In componentWillUnmount, remove listeners

   componentWillUnmount() {
     this.subs.forEach(sub => sub.remove());
   }
   

For more detail, see this PR: https://github.com/react-navigation/react-navigation/pull/3345

Updated:

addListener - Subscribe to updates to navigation lifecycle

React Navigation emits events to screen components that subscribe to them:

• willBlur - the screen will be unfocused

• willFocus - the screen will focus

• didFocus - the screen focused (if there was a transition, the transition completed)

• didBlur - the screen unfocused (if there was a transition, the transition completed)

Ref: https://reactnavigation.org/docs/en/navigation-prop.html#addlistener-subscribe-to-updates-to-navigation-lifecycle

Updated example:

const didBlurSubscription = this.props.navigation.addListener(
  'didBlur',
  payload => {
    console.debug('didBlur', payload);
  }
);

JSON payload:

{
  action: { type: 'Navigation/COMPLETE_TRANSITION', key: 'StackRouterRoot' },
  context: 'id-1518521010538-2:Navigation/COMPLETE_TRANSITION_Root',
  lastState: undefined,
  state: undefined,
  type: 'didBlur',
};

回答2:

componentDidMount / componentWillUnmount does not work in all cases of navigation (like tabs).

You need to use addListener with events didFocus and didBlur to make such actions. See documentation for details

回答3:

Perhaps try componentDidUpdate and set a state within your component. When the state changes the re-render occurs