javascript - 无法从 Firebase Storage UploadTask 更新进度栏

Question

我正在使用 Angular2 和 Firbase 存储。我试图获取“uploadProgress”值来更新(在 HTML 文件中指定)，但不知何故，uploadTask.on 函数中的“uploadProgress”变量可以更新。是因为它在另一个线程上运行吗？这个问题有什么解决方法吗？希望可以有人帮帮我。谢谢

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import { Component } from '@angular/core';
import { AngularFire, FirebaseListObservable } from 'angularfire2';
import * as firebase from 'firebase';

@Component({
  selector: 'app-create-folder',
  templateUrl: './create-folder.component.html'
})

 export class CreateFolderComponent { 

 public fItem: FolderItem;
 public f: File;
 public storageRef: Storage;
 public uploadProgress = 0;


constructor(public af: AngularFire) {}

onSubmit() {

const storageRef = firebase.storage().ref().child('myclient/' +     
this.fItem.file_name);
var uploadTask = storageRef.put(this.f);  


  uploadTask.on('state_changed', function(snapshot){
  this.uploadProgress = (snapshot.bytesTransferred / snapshot.totalBytes) *  
  100;


  });

 }


 }

Answer 1

Is it because it is running on another thread?

因为它在另一个上下文中运行。

要解决问题，请将 this 分配给“state_changed”回调函数之外的某个变量。之后，您可以使用此变量作为对初始 this 实例的引用。

public uploadFile() {
        let self = this;
        ...
        firebaseUploadTask.on('state_changed',
            function progress(snapshot) {
                self.percentage = (snapshot.bytesTransferred / snapshot.totalBytes) * 100;
            },
            function error(error) {},
            function complete() {}
        );
    }