Which lifecycle event is called when a screen appe

问题:

Suppose I have two screens:

• Screen A
• Screen B

I am initially landed on Screen A. When I click on a Button I navigate to Screen B. When I press Back Button, I am again navigated to Screen A.

I want to call an action creator when I am navigated to Screen A as mentioned in above scenario.

I just want to know that which lifecycle event will be called every time when a screen is presented.

Isn't there some event like componentWillAppear()?

Note: I am using react-native with react-navigation for navigation.

回答1:

This can now be done with plain react navigation via their listeners:

In your Component A:

componentDidMount = () => {
  this._componentFocused();

  this._sub = this.props.navigation.addListener(
    'didFocus',
    this._componentFocused
  );
}

componentWillUnmount() {
  this._sub.remove();
}

_componentFocused = () => {
  this.setState({dataToShow});
}

React Navigation docs - Lifecycle

回答2:

When you navigate from one screen to another, the first screen will not be unmounted, but still on the stack, just hide in the background.

What you need might be componentDidFocus, but it's currently in design not avaiable yet, see react-native open issue #51.

You can try this alternative way: react-navigation-addons. With this you can have events focus & blur which may suit your needs.

回答3:

If you use react-native-navigation, you can listen for appearance events: https://wix.github.io/react-native-navigation/#/screen-api?id=listen-to-visibility-events-globally