如何使用Xamarin-Forms下载图像并将其保存在本地存储中。

Question

我想下载一个图像并将其存储在本地存储中的特定文件夹中。

我正在用这个下载图片：

var imageData = await AzureStorage.GetFileAsync(ContainerType.Image, uploadedFilename);
var img = ImageSource.FromStream(() => new MemoryStream(imageData));

Answer 1

创建FileService接口

在共享代码中，创建一个新接口，例如，名为IFileService.cs

 public interface IFileService
 {
      void SavePicture(string name, Stream data, string location="temp");
 }

实现Android

在你的android项目中，创建一个名为"Fileservice.cs“的新类。

确保它派生自之前创建的接口，并使用依赖关系信息对其进行修饰：

[assembly: Dependency(typeof(FileService))]
namespace MyApp.Droid
{
    public class FileService : IFileService
    {
        public void SavePicture(string name, Stream data, string location = "temp")
        {
            var documentsPath = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
            documentsPath = Path.Combine(documentsPath, "Orders", location);
            Directory.CreateDirectory(documentsPath);

            string filePath = Path.Combine(documentsPath, name);

            byte[] bArray = new byte[data.Length];
            using (FileStream fs = new FileStream(filePath , FileMode.OpenOrCreate))
            {
                using (data)
                {
                    data.Read(bArray, 0, (int)data.Length);
                }
                int length = bArray.Length;
                fs.Write(bArray, 0, length);
            }
        }
    }
}

Implementation iOS iOS的实现基本相同：

[assembly: Dependency(typeof(FileService))]
namespace MyApp.iOS
{
    public class FileService: IFileService
    {
        public void SavePicture(string name, Stream data, string location = "temp")
        {
            var documentsPath = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
            documentsPath = Path.Combine(documentsPath, "Orders", location);
            Directory.CreateDirectory(documentsPath);

            string filePath = Path.Combine(documentsPath, name);

            byte[] bArray = new byte[data.Length];
            using (FileStream fs = new FileStream(filePath , FileMode.OpenOrCreate))
            {
                using (data)
                {
                    data.Read(bArray, 0, (int)data.Length);
                }
                int length = bArray.Length;
                fs.Write(bArray, 0, length);
            }
        }
    }
}

为了保存您的文件，在您的共享代码中，调用

DependencyService.Get<IFileService>().SavePicture("ImageName.jpg", imageData, "imagesFolder");

应该可以走了。

Answer 2

public void DownloadImage(string URL)
{
    var webClient = new WebClient();
    webClient.DownloadDataCompleted += (s, e) =>
    {
        byte[] bytes = new byte[e.Result.Length];
        bytes=e.Result; // get the downloaded data
        string documentsPath = Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryPictures).AbsolutePath;

        var partedURL = URL.Split('/');
        string localFilename = partedURL[partedURL.Length-1];
        string localPath = System.IO.Path.Combine(documentsPath, localFilename);
        File.WriteAllBytes(localPath, bytes); // writes to local storage
        Application.Current.MainPage.IsBusy = false;
        Application.Current.MainPage.DisplayAlert("Download", "Download Finished", "OK");
        MediaScannerConnection.ScanFile(Forms.Context,new string[] { localPath }, null, null);
    };
    var url = new Uri(URL);
    webClient.DownloadDataAsync(url);
}

这里你必须使用xamarin forms PCL的依赖服务来调用这个方法，project.This会将你的图片存储到公共文件夹中。我会编辑这个，如果我有时间做一个演示与iOS也。

Answer 3

我真的很喜欢卡兰的方法。

我把它们组合在一起，我想在这里分享它们。实际上，它工作得很好。

public String DownloadImage(Uri URL)
{
    WebClient webClient = new WebClient();

    string folderPath   = System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Personal), "Images", "temp");
    string fileName     = URL.ToString().Split('/').Last();
    string filePath     = System.IO.Path.Combine(folderPath, fileName);

    webClient.DownloadDataCompleted += (s, e) =>
    {
        Directory.CreateDirectory(folderPath);

        File.WriteAllBytes(filePath, e.Result);
    };

    webClient.DownloadDataAsync(URL);

    return filePath;
}