Javascript 试图呈现一个;“装载”;提示,但一旦数据准备就绪,就立即删除数据
我有一个Javascript 试图呈现一个;“装载”;提示,但一旦数据准备就绪,就立即删除数据,javascript,reactjs,asynchronous,react-native,promise,Javascript,Reactjs,Asynchronous,React Native,Promise,我有一个MyFunction(),它为渲染的listView填充数据源,该过程在本地数据库上运行,并在屏幕的构造函数中启动 建造商: constructor(props) { super(props); let MyDataSource = new ListView.DataSource({ rowHasChanged: (r1, r2) => r1 !== r2 }); let MyData = MyFunction(); let MyDataSource
MyFunction()
,它为渲染的listView填充数据源,该过程在本地数据库上运行,并在屏幕的构造函数中启动
建造商:
constructor(props) {
super(props);
let MyDataSource = new ListView.DataSource({ rowHasChanged: (r1, r2) => r1 !== r2 });
let MyData = MyFunction();
let MyDataSource = MyDataSource.cloneWithRows(MyData);
this.state = {
Data: MyData,
DataSource: MyDataSource,};
}
// ..
render() {
return (
<View>
<ListView
dataSource={this.state.dataSource}
renderRow={this.renderRow.bind(this)}
// ..
/>
</View>
);
}
但这会使“加载…”变为空。原因是之后的代码。然后
在之前执行。然后
完成了(我想是吧?)
对于如何实现这一点,我有点困惑,因为我是一个新手,不熟悉如何使用native和js。首先,您不需要状态中的数据,因为您根本不使用它 要解决您的问题,您可以使用以下构造函数:
构造函数(道具){
超级(道具);
getDataFromServer()。然后((响应)=>{
让DataSource=新建ListView.DataSource({
行已更改:(r1,r2)=>r1!==r2
});
这是我的国家({
孤岛加载:false,
DataSource:DataSource.cloneWithRows(响应)
});
});
此.state={
孤岛加载:正确
};
}
constructor(props) {
super(props);
let MyDataSource = new ListView.DataSource({ rowHasChanged: (r1, r2) => r1 !== r2 });
let MyData = MyFunction(); // this is an async now, and will take sometime to finish
let MyDataSource = MyDataSource.cloneWithRows(MyData);
this.state = {
Data: MyData,
DataSource: MyDataSource,
IsLoading: true, // so I added this
};
}
// ..
async MyFunction() {
// ..
// this is what takes time now, and returns a promise, I use .then to set the final data
// it is an async method that has a "await fetch()" inside it
let dataFromServer = await getDataFromServer().then((response) => this.setState({isLoading: false, Data: response}));
// ..
}
render() {
if(this.state.isLoading)
{
return(
<View style={styles.emptyListContainer}>
<Text style={styles.emptyListMessage}>
Loading Data ...
</Text>
</View>
)
}
return (
<View>
<ListView
dataSource={this.state.dataSource}
renderRow={this.renderRow.bind(this)}
// ..
/>
</View>
);
}