Ionic 3 - 延迟文件下载，直到创建文件夹

Question

我正在处理需要将文件下载到移动设备中的自定义文件夹的应用。这是我使用的代码，

downloadImage(imageURL) {

    file.createDir(this.storageDirectory, 'FolderName', false);

    const fileTransfer: FileTransferObject = this.transfer.create();          
    const imageName = imageURL.split('/').pop();

    fileTransfer.download(imageURL, this.storageDirectory + 'FolderName/' + imageName).then((entry) => {
        const alertSuccess = this.alertCtrl.create({
            title: `Download Succeeded!`,
            subTitle: `${imageURL} was successfully downloaded to: ${entry.toURL()}`,
            buttons: ['Ok']
        });
        alertSuccess.present();
    }, (error) => {
        console.log(error)
        const alertFailure = this.alertCtrl.create({
            title: `Download Failed!`,
            subTitle: `${imageURL} was not successfully downloaded. Error code: ${error.code}`,
            buttons: ['Ok']
        });
        alertFailure.present();
    });
}

根据一些参考资料，我试图使用这样的承诺。

downloadImage(imageURL) {
  var folderName = 'FolderName';
  this.createDirectory(folderName);
  console.log('After CreateDirectory');
  this.platform.ready().then(() => {
      const fileTransfer: FileTransferObject = this.transfer.create();        
      const imageName = imageURL.split('/').pop();

      fileTransfer.download(imageURL, this.storageDirectory + 'FolderName/' + imageName).then((entry) => {
          const alertSuccess = this.alertCtrl.create({
              title: `Download Succeeded!`,
              subTitle: `${imageURL} was successfully downloaded to: ${entry.toURL()}`,
              buttons: ['Ok']
          });
          alertSuccess.present();
      }, (error) => {
          console.log(error)
          const alertFailure = this.alertCtrl.create({
              title: `Download Failed!`,
              subTitle: `${imageURL} was not successfully downloaded. Error code: ${error.code}`,
              buttons: ['Ok']
          });
          alertFailure.present();
      });
  });
}

createDirectory(folderName): Promise<Boolean> {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log('createDirectory = ' + folderName)
    }, 5000);

    if(!this.platform.is('cordova')) {
      return false;
    }

    if (this.platform.is('ios')) {
      this.storageDirectory = this.file.externalRootDirectory;
    }
    else if(this.platform.is('android')) {
      this.storageDirectory = this.file.externalRootDirectory;
    }
    else {
      return false;
    }

    this.file.createDir(this.storageDirectory, folderName, false)
    .then((success) => {
      resolve(true);
    })
    .catch((error) => {
      reject(false);
    });
  });
}

当我点击触发此功能的链接时，会显示一个弹出窗口，例如＆＃34;允许MyApp访问照片，媒体......＆＃34;，但在用户按下＆＃34;允许＆＃34之前;按钮，它显示错误弹出窗口。我尝试将其保留在异步块内，但我仍然面临同样的问题。

如何在用户确认弹出窗口之前推迟流程？对此有任何帮助将非常感激。