我有一个函数向服务器发送消息以获取答案，如果答案为真，我希望我的应用程序向用户发送错误。问题是我无法在我编写的 Fetch 函数中等待回调。这是将问题发送到服务器的功能。async donglePaired(){ if (Platform.OS !=='ios'){ var pairedDevices = await BluetoothScanner.getPairedDevices(); console.log('Sending........'); let data={ data:pairedDevices, }; new Api().fetch("bluetoothCheck",{devices:JSON.stringify(data),userid:this.state.probe.UID},(result) => { if (!result.err) return false; console.log("Dongle already paired"); return true; //logNetworkState }); }}这是我写的 Api.fetch 函数fetch(action,data,cb){ let url=Config.URL+"?version="+Config.VERSION+"&action="+action; let post=""; let formData=new FormData(); for(let k in data) formData.append(k,data[k]); for(let k in data) post+="&"+k+"="+encodeURIComponent(data[k]).replace(/%20/g,'+'); console.log(url+post); console.log(url); if (data.batch) console.log(data.batch); let sending=true; fetch(url,{ method: 'post', body: formData }) .then(function(response){ if (true) return response.json(); let txt=response.text(); console.log(txt); return JSON.parse(txt); }) .then( (result)=>{ if (!sending) return; sending=false; console.log(JSON.stringify(result)); if (cb) cb(result); }, (error)=>{ if (!sending) return; sending=false; console.log("fetch error"); console.log(error); if (cb) cb(); } ); setTimeout(()=>{ console.log("http timeout") if (!sending) return console.log("nothing to abort"); if (cb) cb(); },Config.HTTP_TIMEOUT*1000)}}这是我等待第一个函数 donglePaired 的主要代码，如果 donglePaired 返回 true，我会向用户发送错误。let donglePaired = await this.props.app.donglePaired(); if (donglePaired) return this.props.app.setError("ERR_DONGLE");问题是程序不等待 donglePaired，尽管有等待
4 回答
隔江千里
TA贡献1906条经验 获得超10个赞
您可以Promise.race()使用超时函数返回一个。
fetch(action, data, cb) {
let url = Config.URL + "?version=" + Config.VERSION + "&action=" + action;
let post = "";
let formData = new FormData();
for (let k in data) formData.append(k, data[k]);
for (let k in data)
post += "&" + k + "=" + encodeURIComponent(data[k]).replace(/%20/g, "+");
console.log(url + post);
console.log(url);
if (data.batch) console.log(data.batch);
let sending = true;
return Promise.race([
fetch(url, {
method: "post",
body: formData
})
.then(res => res.json())
.then(result => {
if (!sending) return;
sending = false;
return result;
}),
sleep(Config.HTTP_TIMEOUT * 1000)
]);
}
const sleep = ms => new Promise((_, rej) => setTimeout(rej("TIMEOUT"), ms));
它要么返回值，要么拒绝TIMEOUT，或者拒绝 fetch 的错误
然后看起来donglePaired像这样。我用一个包裹它try / catch
async donglePaired() {
if (Platform.OS !== "ios") {
var pairedDevices = await BluetoothScanner.getPairedDevices();
console.log("Sending........");
let data = {
data: pairedDevices
};
try {
let result = await new Api().fetch("bluetoothCheck", {
devices: JSON.stringify(data),
userid: this.state.probe.UID
});
if (!result.err) return false;
console.log("Dongle already paired");
return true;
//logNetworkState
} catch (err) {
console.log(err);
}
}
}
月关宝盒
TA贡献1772条经验 获得超5个赞
这些片段应该让您了解如何等待回调
发送至 API
async function remove_configuration(filename) {
const data = { filename };
const options = {
method: 'POST',
headers: {
'Content-Type': 'application/json'
},
body: JSON.stringify(data)
};
await fetch('/delete', options);
}
只是检索数据
async function display() {
let response = await fetch('/get-available-configurations')
let data = await response.json(); // JSON or Text what do you prefer
// do something with data
}
慕森卡
TA贡献1806条经验 获得超8个赞
你这里的代码不合适
let donglePaired = await this.props.app.donglePaired();
if (donglePaired) return this.props.app.setError("ERR_DONGLE");
异步函数无法正常返回值，除非它是 Promise 请参阅下面我的简单演示！
async function test() {
const result = await asyncRequest()
return result
}
function asyncRequest() {
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve('success')
}, 2000)
})
}
test().then((data) => {
console.log(data)
})
泛舟湖上清波郎朗
TA贡献1818条经验 获得超3个赞
一种可能性是删除async并将其更改为：
donglePaired() {
return new Promise( function(resolve, reject) {
if (Platform.OS !=='ios'){
var pairedDevices = await BluetoothScanner.getPairedDevices();
console.log('Sending........');
let data={
data:pairedDevices,
};
new Api().fetch("bluetoothCheck",{devices:JSON.stringify(data),userid:this.state.probe.UID},(result) => {
if (!result.err) reject(false);
console.log("Dongle already paired");
resolve(true);
//logNetworkState
});
}
reject(false);
});
}
和：
this.props.app.donglePaired().then( (response) => {
// do something here, this will only run if the response is true
});
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