Not able to use props to query API in react js

问题

I have Restaurants component which is responsible for listing restaurants from Zomato Dev APIs. I have passed Category and City from other components to Restaurants component.

I am opening Restaurants component with below code :

this.props.history.push(
        {
            pathname : '/restaurants', 
            valueCategory : this.props.location.valueA,  // CATEGORY
            valueCity : this.state.cities[index] // CITY
        });

I want to use these valueCategory and valueCity in calling /search api.

Code :

class Restaurants extends React.Component {

constructor(props) {
    super(props);
    this.componentDidMount = this.componentDidMount.bind(this);
    this.getRestaurants = this.getRestaurants.bind(this);
}

componentDidMount() {
    // I AM GETTING ERROR 'TypeError: Cannot read property 'name' of undefined' ON THIS LINE
    console.log("Component Did Mount Restaurant : " + this.props.location.valueCity.name);
}

 componentDidUpdate(prevProps, prevState, snapshot){
    console.log("Component Did Update :", prevProps); 
    //THIS PRINTS prevProps, WHICH CONTAINS valueCity and valueCategory but I am unable to access them
    return false;
}

render() {
    let category, city;
    category = '';
    city = '';

    if(!isUndefined(this.props.location.valueCategory)) {
        category = <p>You selected Category as : {this.props.location.valueCategory.categories.name}</p>;
    }

    if(!isUndefined(this.props.location.valueCity)) {
    // STRANGLY, THIS LINE WORKS FINE! WHEN I AM ACCESSING valueCity.name
        city = <p>You selected City as : {this.props.location.valueCity.name}</p>;
    }

    console.log(this.props.location);
    return (
        <div> 
            {category}
            {city}
        </div>
    );
}
}

My question is :

I am able to access {this.props.location.valueCity.name} in render() method
But I am not able to access the same in componentDidMount() or any other method? I am getting crash

TypeError: Cannot read property 'name' of undefined

回答1:

Have you tried componentDidUpdate life cycle method? compare the props incoming to this method

        this.state={
        valueCategory:"",
        valueCity:"" //you can chose any data type, 
        checker:true  
        }

        this.stateUpdater(prevProps){
           let valueCategory={this.props};
           let valueCity={this.props};

           if(this.props.valueCategory===undefined){/*check the data  
           what is incoming and use condition accrodingly*/ 

           this.setState({valueCategory:prevProps.location.valueCategory
           ,checker:false})
           }else{
             //no update
              this.setState({checker:false})
            }
        componentDidUpdate(prevProps, prevState, snapshot){
           console.log("see the props",prevProps,this.props);
           if(this.state.checker)              
              this.stateUpdater(prevProps);
           else{
              console.log("do nothing") 
           }
           return false;
       }

**check and let me know

来源：https://stackoverflow.com/questions/59262734/not-able-to-use-props-to-query-api-in-react-js

标签

reactjs

react-component

zomato-api