英文:
Type 'Promise<any>' is not assignable to type 'string'
问题
我正在使用 async 和 promise 如下所示，我想等待 img 值返回。
ngOnInit(): void {
...
...
this.auth.msg.subscribe((res) => {
let img = this.fetchImage(this.user.id);
this.url = img; // 获取错误
...
});
}
async fetchImage(Id) {
let result: any;
let payload = {
Id: Id
};
result = await this.Sev.getPicture(payload).toPromise();
return result.response;
}
当我将 img 响应传递给其他变量时出现此错误：
类型 'Promise
' 不能赋值给类型 'string'
英文:
I'm using async and promise like given below, I want to wait for the img value to be returned.
ngOnInit(): void {
...
...
this.auth.msg.subscribe((res) => {
let img=this.fetchImage(this.user.id);
this.url=img; // getting error
...
});
}
async fetchImage(Id) {
let result: any;
let payload = {
Id: Id
};
result = await this.Sev.getPicture(payload).toPromise();
return result.response;
}
When I pass img response to some other variable getting this error:
> Type 'Promise<any>' is not assignable to type 'string'
答案1
得分: 2
The error message mentions that your fetchImage returns a Promise.
To get the value from the Promise, either:
- 使用回调函数
this.auth.msg.subscribe((res: any) => {
this.fetchImage(this.user.id)
.then((value) => {
this.url = img;
});
});
- 使用 async/await
this.auth.msg.subscribe(async (res: any) => {
let img = await this.fetchImage(this.user.id);
this.url = img;
});
.toPromise() 已经在 RxJS 7 中弃用。建议根据RxJS文档中所述，将 .toPromise() 迁移到 firstValueFrom/lastValueFrom：
import { lastValueFrom } from 'rxjs';
async fetchImage(Id)
{
let result: any;
let payload = {
Id: Id
};
result = await lastValueFrom(this.Sev.getPicture(payload));
return result.response;
}
英文:
The error message mentions that your fetchImage returns a Promise.
To get the value from the Promise, either:
- A callback function
this.auth.msg.subscribe((res: any) => {
this.fetchImage(this.user.id)
.then((value) => {
this.url = img;
});
});
- Use async/await
this.auth.msg.subscribe(async (res: any) => {
let img = await this.fetchImage(this.user.id);
this.url = img;
});
While .toPromise() is deprecated from RxJS 7. Recommend migrating the .toPromise() with firstValueFrom/lastValueFrom as stated in the RxJS documentation:
import { lastValueFrom } from 'rxjs';
async fetchImage(Id)
{
let result: any;
let payload = {
Id: Id
};
result = await lastValueFrom(this.Sev.getPicture(payload));
return result.response;
}
答案2
得分: 1
你可以尝试使用 switchMap。
this.auth.msg.pipe(
switchMap(_ => this.fetchImage(this.user.id))
).subscribe((img) => {
this.url = img;
...
});
英文:
You could try switchMap
this.auth.msg.pipe(
switchMap(_ => this.fetchImage(this.user.id))
).subscribe((img) => {
this.url=img;
...
});
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