为什么map（）返回一个未定义值的数组？ [英] Why does map() return an array with undefined values?
问题描述
我正在尝试构建过滤系统。有两个过滤菜单。一个是房间数，另一个是房产类型。我已经从api加载了json文件到space对象。但是当我尝试将所有这些空格传递给SpaceFilterResults组件时，我的空间数组返回为[undefined，undefined]。
I am trying to build filter system. There is two filter menu. One is number of room and another is type of property. I have loaded json file from an api to space object. But when i try to pass all those spaces to SpaceFilterResults component my space array returns as [undefined, undefined].
我的过滤器代码
class FilterSpace1 extends React.Component {
constructor() {
super();
this.handleFormInput = this.handleFormInput.bind(this);
this.state = {
space:[],
propertyType: 0,
rooms: 0
}
}
componentDidMount(){
this.loadRoomFromServer();
}
loadRoomFromServer(){
$.ajax({
url:'/api/rentals/',
dataType:'json',
success: (data) => {
console.log('data',data);
this.setState({space: data.results});
console.log('success',this.state.space);
},
error: (xhr, status, err) => {
console.error(url, status, err.toString());
}
});
}
handleFormInput(propertyType, rooms) {
this.setState({
propertyType: propertyType,
rooms: rooms
})
}
render() {
let space = _.map(this.state.space, (space,id) => {
console.log('space is',space); // has an array as shown below
<SpaceFilterResults
key = {id}
space={space}
propertyType={this.state.propertyType}
rooms={this.state.rooms}
/>
});
console.log('space',space); //i get space [undefined, undefined] instead of all the spaces
return (
<div className="filter">
<SpaceFilterMenu
propertyType={this.state.propertyType}
rooms={this.state.rooms}
onFormInput={this.handleFormInput}
/>
{space}
</div>
)
}
}
class SpaceFilterMenu extends React.Component {
constructor() {
super();
this.handleChange = this.handleChange.bind(this);
}
handleChange() {
this.props.onFormInput (
this.refs.propertyTypeInput.value,
this.refs.roomsInput.value
);
}
render() {
return (
<div className="container">
<div className="row">
<form className="filter-menu">
<label htmlFor="roomsInput">Number of rooms</label>
<select id="roomsInput" ref="roomsInput" onChange={this.handleChange}>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="6">6</option>
</select>
<label htmlFor="propertyTypeInput">propertyType</label>
<select id="propertyTypeInput" ref="propertyTypeInput" onChange={this.handleChange}>
<option value="Appartment">Appartment</option>
<option value="House">House</option>
<option value="Shop">Shop</option>
<option value="Bunglow">Bunglow</option>
</select>
</form>
</div>
</div>
);
}
}
class SpaceFilterResults extends React.Component {
constructor() {
super();
}
render() {
var results = [];
this.props.space.map((space) => {
if(this.props.roomsInput===0){
results.push(<Space space = {space} />);
}
else if (space.roomsInput === this.props.roomsInput) {
results.push(<Space space={space} />);
}
});
this.props.space.map((space) => {
if (this.props.propertyType === 0 ) {
results.push(<Space space={space} />);
}
else if (space.propertyType === this.props.propertyType) {
results.push(<Space space={space} />);
}
});
return (
<div className="container">
<div className="row">
<div className="col-md-4">
<div className="filter-results">
<ul className="blocks blocks_3up">
{results}
</ul>
</div>
</div>
</div>
</div>
)
}
}
class Space extends React.Component {
constructor () {
super();
}
render () {
return (
<li>
<div className="feature">
<div className="feature-hd">
<h2 class="hdg hdg_2">{this.props.space.listingName}</h2>
</div>
<div className="feature-bd">
<p>{this.props.space.room}</p>
</div>
<div className="feature-ft">
<p>{this.props.space.property}% rooms</p>
</div>
</div>
</li>
)
}
}
export default FilterSpace1;
我的json文件看起来像（/ api / rental /）
console.log的输出（'space is '，space）给出的空间是Object {id：1，renter：admin，gallery：Array [2]，ownerName：tushant khatiwada，电子邮件：tushant@gmail.com...}
the output of console.log('space is',space) gives space is Object {id: 1, renter: "admin", gallery: Array[2], ownerName: "tushant khatiwada", email: "tushant@gmail.com"…}
我做错了什么？如何将这些所有空间数据传递给SpaceFilterResults组件？
What have i done wrong? How can i pass these all space data to SpaceFilterResults component?
推荐答案
此地图回调：
let space = _.map(this.state.space, (space, id) => {
<SpaceFilterResults
key = {id}
space={space}
propertyType={this.state.propertyType}
rooms={this.state.rooms}
/>
});
不会返回任何内容。
这里是另一个不起作用的例子：
Here is another example that doesn’t work:
let nums = [1, 2, 3].map(x => { x * 2 })
如果箭头函数体是一个块，它就不会t隐含地返回任何内容。
// { x * 2; } is a block so this doesn’t work
let nums = [1, 2, 3].map(x => { x * 2; })
// x * 2 is an expression so this works
let nums = [1, 2, 3].map(x => x * 2)
如果您在箭头功能中使用 {和} ，则必须还使用 return 声明：
If you use { and } inside an arrow function, you must also use a return statement:
// { x * 2 } is a block with a return so this works
let nums = [1, 2, 3].map(x => { return x * 2; })
因此，要修复代码，请通过删除 {和} ：
So to fix your code, either make the arrow function body an expression by removing { and }:
let space = _.map(this.state.space, (space, id) =>
<SpaceFilterResults
key = {id}
space={space}
propertyType={this.state.propertyType}
rooms={this.state.rooms}
/>
);
或将其保留为块但添加显式返回声明：
or keep it as a block but add an explicit return statement:
let space = _.map(this.state.space, (space, id) => {
return (
<SpaceFilterResults
key = {id}
space={space}
propertyType={this.state.propertyType}
rooms={this.state.rooms}
/>
);
});
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