0x00.添加引用

using System;
using System.Threading.Tasks;
using Windows.Networking.BackgroundTransfer;
using Windows.Storage;

0x01.下载

Uri uri = new Uri(imageUri);//需要下载图片的Uri,exp:http*****.jpg
BackgroundDownloader backgroundDownload = new BackgroundDownloader();
StorageFolder folder = await KnownFolders.PicturesLibrary.CreateFolderAsync("Acafe", CreationCollisionOption.OpenIfExists);//此处为下载路径,可是要Openfolder改为自定义路径
StorageFile newFile = await folder.CreateFileAsync(imageName, CreationCollisionOption.OpenIfExists);//创建文件，需要定义文件名
DownloadOperation download = backgroundDownload.CreateDownload(uri, newFile);//创建下载器
await download.StartAsync();//启动