绑定传递给组件的函数

Question

阅读这个SO答案,我明白当我将函数传递给react组件时,我必须在构造函数中绑定一个函数,就像这样

 constructor(props) {
    super(props);

    //binding function
    this.renderRow = this.renderRow.bind(this);
    this.callThisFunction = this.callThisFunction.bind(this);
    }

或者我会得到这样的错误.

null不是对象:评估 this4.functionName

按照这个建议,我在构造函数中绑定了函数,但我仍然得到相同的错误.

我正在使用React Native制作一个Master/Detail应用程序,该应用程序基于react native repo中的Movies示例,但我不使用此语法

var SearchScreen = React.createClass({

(这是回购的内容)而是这种ES6风格的语法

class ListOfLists extends Component {

在我的列表视图中,我渲染这样的行.

  class MovieList extends Component{
      constructor(props){
        super(props);
        this.selectMovie = this.selectMovie.bind(this);
        this.state = {
          dataSource: new ListView.DataSource({
            rowHasChanged: (row1, row2) => row1 !== row2,
          }),
        };
      }
          renderRow(
            movie: Object,
            sectionID: number | string,
            rowID: number | string,
            highlightRowFunc: (sectionID: ?number | string, rowID: ?number | string) => void,
          ) {
          console.log(movie, "in render row", sectionID, rowID);
            return (
              <ListCell 
                onSelect={() => this.selectMovie(movie)}
                onHighlight={() => highlightRowFunc(sectionID, rowID)}
                onUnhighlight={() => highlightRowFunc(null, null)}
                movie={movie}
              />
            );
          }

       selectMovie(movie: Object) {
        if (Platform.OS === 'ios') {
          this.props.navigator.push({
            title: movie.name,
            component: TodoListScreen,
            passProps: {movie},
          });
        } else {
          dismissKeyboard();
          this.props.navigator.push({
            title: movie.title,
            name: 'movie',
            movie: movie,
          });
        }
      }
     render(){
        var content = this.state.dataSource.getRowCount() === 0 ?
            <NoMovies  /> :
            <ListView
             ref="listview"
             renderSeparator={this.renderSeparator}
             dataSource={this.state.dataSource}
             renderFooter={this.renderFooter}
             renderRow={this.renderRow} 
             automaticallyAdjustContentInsets={false}
             keyboardDismissMode="on-drag"
             keyboardShouldPersistTaps={true}
             showsVerticalScrollIndicator={false}
             renderRow={this.renderRow}
     }

关键是this.selectMovie(movie).当我单击带有电影名称的行时,出现错误

null不是对象: evaluating this4.selectMovie

问题:为什么它告诉我null is not an object或者为什么该函数为null？

更新:

我在代码中添加了render方法,以显示renderRow使用的位置

Answer 1

在不修改代码的情况下处理此问题的方法是添加 this.renderRow = this.renderRow.bind(this)到类构造函数中.

class New extends Component{   
  constructor(){
    this.renderRow = this.renderRow.bind(this)
  }

  render(){...} 
}

你必须添加属性renderRow = { this.renderRow },实际上与执行renderRow 绑定到空的对象.尝试安慰this中renderRow,你会发现它是GlobalObject代替Class MovieList你的愿望.