收到此错误：TypeError：无法读取null的属性'setMaxNumberPointsPerLink'

Question

我正在使用this库来绘制图表。

我将代码这样保存在componentWillMount中，

class FlowDiagramEngine extends Component {

constructor(props) {
    super(props);
    this.flowJson = this.props.flowDiagramData;
    this.state = {};
}
componentWillMount() {
    console.log("this.flowJson :"+this.flowJson); // this is empty
    var engine = ...
    engine.setDiagramModel(model);
    .... all code to construct diagram
    this.setState({engine: engine});
}
render() {
    return (
        <div>
            <FlowDiagramWidget className="srd-demo-canvas" {...this.state} />   
        </div>
    )
}

}

FlowDiagramWidget

class FlowDiagramWidget extends Component {

    render() {
        return (
            <div>
                <Grid container
                    justify="space-between"
                    alignItems="center">

                  <DiagramWidget className="srd-demo-canvas" diagramEngine={this.props.engine} />   
                </Grid>
            </div>
        )
    }
}
export default FlowDiagramWidget

我希望在componentWillMount中使用Redux道具，但是在执行生命周期方法componentWillMount期间，异步道具为空。 redux道具已在构造函数中正确初始化。

每当我将componentWillMount更改为componentDidMount时，都会出现以下错误。为什么会发生这种情况？

TypeError: Cannot read property 'setMaxNumberPointsPerLink' of null
    at DiagramWidget.render (main.js:1)
    at ReactCompositeComponentWrapper._renderValidatedComponentWithoutOwnerOrContext (ReactCompositeComponent.js:796)
    at ReactCompositeComponentWrapper._renderValidatedComponent (ReactCompositeComponent.js:819)
    at ReactCompositeComponentWrapper.performInitialMount (ReactCompositeComponent.js:359)
    at ReactCompositeComponentWrapper.mountComponent (ReactCompositeComponent.js:255)
    at Object.mountComponent (ReactReconciler.js:43)
    at ReactDOMComponent.mountChildren (ReactMultiChild.js:234)
    at ReactDOMComponent._createInitialChildren (ReactDOMComponent.js:701)
    at ReactDOMComponent.mountComponent (ReactDOMComponent.js:520)
    at Object.mountComponent (ReactReconciler.js:43)

编辑：我在父容器中有这个

function mapStateToProps(state, ownProps) {
  return {
     flowDiagramData: state.appReducer.flowDiagramData
  }
}