我的React下拉列表有问题,我想在列表中预先选择一个值,但我不知道该怎么做。
例如:在列表中选择一个值之前,我想要在选择一个值之前先获得一个值,例如,我从数据库中获取的第一个元素。
App类:
class App extends Component {
constructor(props) {
super(props);
this.state = {
data: [],
station: [],
stationValue: ''
}
}
getParking = async () => {
try {
const reponse = await axios.get(URL + "station/");
this.setState({
station: reponse.data['hydra:member']
});
} catch (e) {
console.log(e)
}
};
getData = async () => {
try {
const response = await axios.get(URL + "events?station=" + this.state.stationValue);
this.setState({
data: response.data["hydra:member"]
});
} catch (error) {
console.log(error)
}
};
componentDidMount() {
this.getData();
this.getParking()
setInterval(this.appendData, 1000)
}
setStation=(stationValue)=>{
this.setState({stationValue:stationValue})
}
render() {
const {data, station} = this.state;
return (
<div>
<header>
<Dropdown dataStation={station} setStation={this.setStation} value={this.handleChange}/>
</header>
{
data.map((item, key) =>
<div key={key}>
<>
{item.label}
</>
</div>
)
}
</div>
)
}
}
composent DropDown:
const Dropdown = ({dataStation, setParking, value}) => {
const [showMenu, setShowMenu] = useState(false);
const [selectItem, setSelectItem] = useState(showMenu);
const showList = () => {
setShowMenu(!showMenu)
};
const toggleSelected = (list) => {
setSelectItem(list.name);
setShowMenu(false)
};
return (
<>
<div className="dropdown-list-style" onClick={showList}>
<div style={{display: 'inline'}}>
{showMenu
? (<div style={{textAlign: 'right'}}><ChevronUp/></div>)
: (<div style={{textAlign: 'right'}}><ChevronDown/></div>)
}
{selectItem}
</div>
</div>
<div className="dropdown-list-style" style={{display: showMenu ? 'block' : 'none'}}>
{
dataStation.map((list, index) =>
<div key={index} onClick={() => toggleSelected(list); props.setStation(list)}}>
{list.name}
</div>
)
}
</div>
</>
)};
我尝试了
dataStation[0].name
但是不好,有人可以帮我吗?
答案 0 :(得分:2)
您可以使用useEffect
挂钩。当车站的获取请求完成并且道具更改时,它将从数组中选择第一个元素作为默认值。
useEffect(() => {
if (Array.isArray(dataStation) && dataStation[0]) {
selectItem(dataStation[0].name);
}
}, [dataStation]);