Angular:承诺内的异步等待-事件侦听器
在这个问题上我已经挣扎了一天了。 我想创造这种情况:Angular:承诺内的异步等待-事件侦听器,angular,typescript,promise,async-await,Angular,Typescript,Promise,Async Await,在这个问题上我已经挣扎了一天了。 我想创造这种情况: <img [src]="userdp | async" /> 在getUserDp()中,以下是代码: async getUserDp() { return await this._http.get(APIvars.APIdomain+'/'+APIvars.GET_USER_DP, { responseType: 'blob' }).toPromise().then( image =>
<img [src]="userdp | async" />
在getUserDp()中,以下是代码:
async getUserDp() {
return await
this._http.get(APIvars.APIdomain+'/'+APIvars.GET_USER_DP, { responseType: 'blob' }).toPromise().then( image => {
if(image['type'] === 'application/json') {
return null;
}
const reader = new FileReader();
reader.addEventListener('load', () => {
**return this._dom.bypassSecurityTrustResourceUrl(reader.result.toString());**
});
}, false);
if (image) {
reader.readAsDataURL(image);
}
});
}
Promise没有等待读卡器加载到EventListener中,任何立即返回语句都会给出预期的结果,粗体的一行是要返回的主要数据
谢谢取代您的承诺
reader.onload = function (e) {
};
通过创建一个承诺返回的FileReader方法,您可以在一个地方摆脱回调业务,从而使您的生活更轻松——以及未来代码读者的生活更轻松
// return a promise that resolves on the 'load' event of FileReader
async function readAsDataURL(image) {
const reader = new FileReader();
return new Promise((resolve, reject) => {
reader.addEventListener('load', () => {
resolve(reader.result.toString());
});
// consider adding an error handler that calls reject
reader.readAsDataURL(image);
});
}
现在,文件处理代码已经“promisified”,它更容易使用
async getUserDp() {
// temp vars so we can read the code
const url = APIvars.APIdomain+'/'+APIvars.GET_USER_DP;
const options = { responseType: 'blob' };
// await replaces .then() here
const image = await this._http.get(url, options).toPromise();
// not sure whether this is right, just following OP logic here
// bail if the image (result of the get()) is falsey or is of type json
if (!image || image['type'] === 'application/json') return null;
// simple to call to await file reading
const readerResult = await readAsDataURL(image);
return this._dom.bypassSecurityTrustResourceUrl(readerResult);
}
你能解释一下吗?我对异步有点陌生
async getUserDp() {
// temp vars so we can read the code
const url = APIvars.APIdomain+'/'+APIvars.GET_USER_DP;
const options = { responseType: 'blob' };
// await replaces .then() here
const image = await this._http.get(url, options).toPromise();
// not sure whether this is right, just following OP logic here
// bail if the image (result of the get()) is falsey or is of type json
if (!image || image['type'] === 'application/json') return null;
// simple to call to await file reading
const readerResult = await readAsDataURL(image);
return this._dom.bypassSecurityTrustResourceUrl(readerResult);
}