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我有MyFunction()
填充我的渲染的listView的数据源,并且该进程在本地数据库上运行,并从屏幕的构造函数开始。试图呈现“加载”提示,但数据一旦准备就绪
构造:
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>
);
}
现在,我想MyFunction()
从远程数据库检索数据,因此它是将之前的数据已经准备好了一段时间服用。
我想在屏幕上显示“加载”消息,然后在数据准备就绪时更新屏幕。我修改我的代码如下:
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>
);
}
但是,这呈现“加载..”然后为空。原因是.then
之后的代码正在执行之前.then
完成(我猜?)
我有点困惑如何实现这一点,因为我是新的反应原生和js。请和谢谢