等待可觀察的完成-Angular

Question

我正在使用Angular和Firebase存儲上載圖像，當我嘗試在tap內的console.log打印urlImg時，我urlImg了一個undefined的問題。

 this.snapshot = this.snapshot = this.task.snapshotChanges().pipe(
      finalize(() => {
        this.storage
          .ref(path)
          .getDownloadURL()
          .subscribe(url => {
            this.urlImg = url; // with this you can use it in the html
          });
      }),
      tap(snap => {
        if (snap.bytesTransferred === snap.totalBytes) {
          // Update firestore on completion
          //Code to upload on completion
          console.log("url");
          console.log(this.urlImg);
        }
      })
    );

Answer 1

一種選擇是利用已完成的訂閱部分。 然后，您可以確保this.urlImg具有值。

.subscribe(
   url => this.urlImg = url,
   err => console.error('Request for URL failed: ' + err),
   () => {
      // operations when URL request is completed
   }
)