Using for loops and switch cases in React to dynamically render different components

问题

I am trying to render components conditionally using switch case in React JSX. I am trying to build something that reads from a specific json structure and renders the data. Since there can be many different components and data, I am trying to render it dynamically. See my code below, I am not getting any errors but the components aren't getting rendered. Inside my html , I can only see . This means the loop isn't working. I tried using the same loop in vanilla JS and it works.

var myPackage = [{
    sectionInfo:[{
        elementType: 1,
        text: "This is text from element type 1"
    }]
},
{
    sectionInfo:[{
        elementType: 2,
        text: "This is text from element type 2"
    }]
}];
var App = React.createClass({

    render: function(){
        var elements = [];
        elements = myPackage.map(function(myObj){
            myObj.sectionInfo.map(function(myObj1){
                switch(myObj1.elementType){
                    case 1: return(
                                <Component1 text = {myObj1.text}/>
                            );
                            break;
                    case 2: return(
                                <Component2 text = {myObj1.text}/>
                            )
                            break;      
                }
            })
        });
        return(
            <div className="App">
                {elements}
            </div>
        )
    }
});
var Component1 = React.createClass({
    render:function(){
        return(
            <div className = "element1">
                {this.props.text}
            </div>
        )
    }
});
var Component2 = React.createClass({
    render:function(){
        return(
            <div className = "element2">
                {this.props.text}
            </div>
        )
    }
});
ReactDOM.render(<App/>,document.getElementById('container'));

Edit: Made a few additions to the code, and now I am facing a new problem. Here is the new code:

var App = React.createClass({

        render: function(){
            var elements = [];
            elements = myPackage.map(function(myObj){
                return(
                       <div>
                           myObj.sectionInfo.map(function(myObj1){
                           switch(myObj1.elementType){
                           case 1: return(
                                    <Component1 text = {myObj1.text}/>
                                );
                                break;
                           case 2: return(
                                    <Component2 text = {myObj1.text}/>
                                )
                                break;      
                        }
                        }
                  </div>
                )
                });
        return(
            <div className="App">
                {elements}
            </div>
        )
    }
});

I want to render each time inside a div. So that if one section has more than 3 elements, then all 3 must be inside a div.

回答1:

You should return value from first .map, in your case it is result from inner .map

var elements = myPackage.map(function(myObj){
  return myObj.sectionInfo.map(function(myObj1) {
     // ...  
  });
});

Update:

Based on your new update, you can change your code like this

var App = React.createClass({

  section: function(myObj, parentIndex) {
    return myObj.sectionInfo.map(function(myObj1, index) {
      const key = parentIndex + '.' + index;

      switch(myObj1.elementType) {
        case 1:
          return <Component1 text = {myObj1.text} key={ key } />
        case 2:
          return <Component2 text = {myObj1.text} key={ key } />
      }
    });
  },

  render: function() {
    var elements = myPackage.map(function(myObj) {
      return <div>
        { this.section(myObj, index) }
      </div>
    }, this);

    return <div className="App">
     { elements }
    </div>;
  }
});

回答2:

To do a switch case in JSX do it as follow:

   {{
    sectionA: (
      <SectionAComponent />
    ),
    sectionB: (
      <SectionBComponent />
    ),
    sectionC: (
      <SectionCComponent />
    ),
    default: (
      <SectionDefaultComponent />
    )
  }[section]}

回答3:

for inline / not created new function ,you can use this way

<div>
    {(() => {
        switch (myObj1.elementType) {
            case 'pantulan':
                return <Component1 text = {myObj1.text} key={ key } />
            default :
                null
        }
    })()}
</div>

回答4:

Recommended way by React: React Docs

const components = {
  photo: PhotoStory,
  video: VideoStory
};

function Story(props) {
  // Correct! JSX type can be a capitalized variable.
  const SpecificStory = components[props.storyType];
  return <SpecificStory story={props.story} />;
}

回答5:

You are missing a return as stated in the answer by Alexander T, but I would also recommend adding a key to each of your elements. React depends on this value for it's diff'ing algorithm, you could do something like:

render: function(){
  var elements = myPackage.map(function(myObj, pIndex){
    return myObj.sectionInfo.map(function(myObj1, sIndex){
      var key = pIndex + '.' + sIndex;            
      switch(myObj1.elementType) {
        case 1: return(
          <Component1 key={key} text={myObj1.text}/>
        );
        case 2: return(
          <Component2 key={key} text={myObj1.text}/>
        )
      }
    })
  });
  return(
    <div className="App">
      {elements}
    </div>
  )
}

Read here for more info: https://facebook.github.io/react/docs/multiple-components.html#dynamic-children

来源：https://stackoverflow.com/questions/37782776/using-for-loops-and-switch-cases-in-react-to-dynamically-render-different-compon