react-native异步函数返回promise但不是我的json数据? [英] react-native async function returns promise but not my json data?
问题描述
我正在学习本机响应,但是遇到了问题.为什么从异步函数返回时获取数据会返回一个Promise,但在异步函数本身中,它会正确返回一个对象数组?
I'm learning react-native, and I'm running into an issue. Why does getting data on return from an async function return a promise, but in the async function itself, it correctly returns an array of objects?
在componentDidMount()
上,我调用了我的异步函数,该函数依次提取到api网址:
On componentDidMount()
, I call my async function which in turn does a fetch to an api url:
componentDidMount() {
let data = this.getData();
console.log(data); // <-- Promise {_40: 0, _65: 0, _55: null, _72: null}
this.setState({
dataSource:this.state.dataSource.cloneWithRows(data),
})
}
async getData() {
const response = await fetch("http://10.0.2.2:3000/users", {
method: 'GET',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json',
}
});
const json = await response.json();
console.log(json); // <-- (5) [Object, Object, Object, Object, Object]
return json;
}
在console.log(json)
中,我获得了json对象的正确列表,并且可以使用json[0].name
访问它们.但是后来,console.log(data)
返回一个带有奇数数据的promise:
In console.log(json)
, I get the correct list of json objects, and I can access them with json[0].name
. But later, console.log(data)
returns a promise with odd data:
Promise {_40: 0, _65: 0, _55: null, _72: null}
...,我再也找不到我的json对象.为什么是这样?更重要的是,如何在componentDidMount()
中检索我的json数据,以便可以将其设置为dataSource
?
... and I can no longer find my json objects. Why is this? More importantly, how can I retrieve my json data in componentDidMount()
so that I can set it as the dataSource
?
推荐答案
由于getData()
是一个承诺,因此您应该能够在then
块中获取数据,如下所示:
Since getData()
is a promise, you should be able to obtain the data in a then
block as follows:
componentDidMount() {
this.getData()
.then((data) => {
this.setState({
dataSource:this.state.dataSource.cloneWithRows(data),
})
});
}
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