从先前调用的方法获得响应后如何调用方法

Question

我正在尝试将文件数组保存到 Spring Boot 服务器。一次保存一个文件。我正在使用 for 循环迭代文件数组并请求保存每个文件。在这里，我希望仅在获得第一个文件的响应后才进行下一次调用。我已经尝试了下面给出的代码，但我无法实现它。

组件.ts

public uploadNewsFiles() {

for (let index = 0; index < this.files.length; index++) {
  debugger;
  var body = new FormData();
 // alert(this.files[index].name);
  body.append('file', this.files[index]);
  this.uploading.push(true);
  this.uload(body,this.newsId,this.getFileDescriptionFormGroup(index)
  .controls['des'].value,index).then((status:any)=>
  {
    if (status.status === 'success') {
    //  alert('success');
      body.delete('file');
      this.uploading[index] = false;
      this.uploadingStatus.push(true);
     
    } else {
      body.delete('file');
      this.uploading[index] = false;
      this.uploadingStatus.push(false);
    }
  },(err)=>alert('failed'))
  }

   // body.append('newsId',this.newsId);
   }

  async uload(body,newsId,desc,index) {
  return await this.service.saveFiles(body, newsId,desc).toPromise();
  }

service.ts

public saveFiles(body,newsId,des) {

return this.http.post(this.url + '/saveFiles? 
newsId='+newsId+'&fileDescription='+des,body);
}

Answer 1

由于您使用的是 Angular，我们可以利用 rxjs 库而不是使用 toPromise 并从 http 调用中链接 observables，例如：

function modUploadFiles() {
  this.files
    .map((file, index) => {
      const body = new FormData();
      body.append("file", file);

      const newsId = this.newsId;

      const desc = this.getFileDescriptionFormGroup(index).controls["des"]
        .value;

      return this.service.saveFiles(body, newsId, desc).finally(status => {
        body.delete("file");
        this.uploading[index] = false;
        this.uploadingStatus.push(status.status === "success");
      })
    })
    .reduce((acc, next) => acc.flatMap(() => next))
    .subscribe(result => {/*Do something*/});
}

您可以在以下问题中查看更多信息：

Chaining Observables in RxJS

Answer 2

你可以使用asyncawait。

async uploadNewsFiles() {

for (let index = 0; index < this.files.length; index++) {
  var body = new FormData();
  body.append('file', this.files[index]);
  this.uploading.push(true);
  await this.uload(body,this.newsId,this.getFileDescriptionFormGroup(index)
  .controls['des'].value,index).then((status:any)=>
  {
     if (status.status === 'success') {
       body.delete('file');
       this.uploading[index] = false;
       this.uploadingStatus.push(true);
// here we are calling the 
     } else {
       body.delete('file');
       this.uploading[index] = false;
       this.uploadingStatus.push(false);
     }
    },(err)=>alert('failed'))
  }
}

uload(body,newsId,desc,index) {
  return new Promise((resolve, reject) => {
     this.service.saveFiles(body, newsId,desc).toPromise().then(resp => {
        resolve(resp); // here we are resolving our promise
     });
  });
}

服务

public saveFiles(body,newsId,des) {
 return this.http.post(this.url + '/saveFiles? 
         newsId='+newsId+'&fileDescription='+des,body);
}

希望对你有帮助。