React-native States

Question

我在构造函数中声明了状态并尝试从renderScene调用它，但this.state总是null出错了什么？

我的代码是;

var _=require('underscore');
class ReactNotes extends React.Component {
 constructor (props) {
   super(props);
        this.state = {
                      selectedNote: {title:"", body:""},
                      notes: {
                                1: {title: "Note 1", body: "body", id: 1},
                                2: {title: "Note 2", body: "body", id: 2}
                            }
                    };


} render () { 
  return (

        <Navigator initialRoute={{name: 'home'}}
        renderScene={this.renderScene}
        navigationBar=
        {
          <Navigator.NavigationBar
        routeMapper={NavigationBarRouteMapper}
        style={styles.navBar}
          />
        }
        /> );
}

renderScene (route, navigator) {
switch (route.name) {
  case 'home':
    return (

            <HomeScreen navigator={navigator} notes= {_(this.state.notes).toArray()} onSelectNote={(note) => navigator.push({name:"createNote", note: note})}/>

            );
  case 'createNote':
    return (
            <NoteScreen note={this.state.selectedNote}
            onChangeNote={(note) => this.updateNote(note)}/>
            );
} }

}

输出如下：

Answer 1

您可以使用箭头功能

绑定您的功能

renderScene = (route, navigator) => {
  //...
}
//then call your function in your navigator as  
renderScene={this.renderScene}

或

// You can use bind() to preserve `this`
renderScene={this.renderScene.bind(this)}>

// Or you can use arrow function this way
renderScene={() => this.renderScene()}>