What is correct lifecycle method in React 16.3 to update canvas from props?

Question

I have a Canvas component, which looks approximately like this:

<

相关标签:

Answer 1

I found this because I had a sort of similar problem but not completely the same. The solution that works for me is just to put all the relevant code in shouldComponentUpdate:

(the if statement used to be in componentWillReceiveProps)

  shouldComponentUpdate (nextProps, nextState) { // no more random renders
    if (
      (nextProps.nightMode !== this.props.nightMode) ||
      (nextProps.language  !== this.props.language)
    ) {
      this.props.setRefresh(true)                       // setTimeout means after current operation
      setTimeout(() => this.props.setRefresh(false), 1) // so loading will show for longer than 1ms
    }

    return this.props.refresh !== nextProps.refresh
  }

Answer 2

Use componentDidUpdate for DOM manipulations like this. A shouldComponentUpdate won’t really make a difference for a component with a single child that always has the same props. So you should be able to remove it without a significant difference in performance.

If you've profiled the application and determined that in this particular case it does make a difference, you can hoist the element into constructor.

This way React will skip over it completely (which effectively works the same way as shouldComponentUpdate):

class Canvas extends React.Component {
  constructor(props) {
    super(props);
    this._ctx = null;
    this._child = <canvas ref={node => {
      this._ctx = node ? node.getContext('2d') : null
    } />;
  }

  componentDidUpdate(prevProps){
    // Manipulate this._ctx here
  }

  render() {
    // A constant element tells React to never re-render
    return this._child;
  }
}

You could also split it into two components:

class Canvas extends React.Component {
  saveContext = ctx => {
    this._ctx = ctx;
  }

  componentDidUpdate(prevProps){
    // Manipulate this._ctx here
  }

  render() {
    return <PureCanvas contextRef={this.saveContext} />;
  }
}


class PureCanvas extends React.Component {
  shouldComponentUpdate() {
    return false;
  }

  render() {
    return (
      <canvas
        ref={node => node ? this.props.contextRef(node.getContext('2d') : null)}
      />;
  }
}