无法从 URL Xamarin Form 下载图像 [英] Unable to download Image from URL Xamarin Form

问题描述

我正在开发一个 Xamarin 应用程序，它从数据库中检索信息，拍摄/选择照片并将它们上传到远程服务器，从远程服务器显示此图像，用户可以通过点击并按下按钮来删除它们.最后一步是将存储在服务器中的图像下载到本地设备库中.

I am developing a Xamarin app which retrives info from DB, take/choose photo and upload them to remote server, display this images from the remote server and the user can delete them by tap on and press a button. The final step is to download the images stored in the server to the local device gallery.

这是我当前的按钮点击事件:

This is my current button click event:

private void button_download_image_Clicked(object sender, EventArgs e)
{
        Uri image_url_format = new Uri(image_url);
        WebClient webClient = new WebClient();
        try
        {              
            webClient.DownloadDataAsync(image_url_format);
            webClient.DownloadDataCompleted += webClient_DownloadDataCompleted;
        }
        catch (Exception ex)
        {
            DisplayAlert("Error", ex.ToString(), "OK");
        }
}

在 webClient_DownloadDataCompleted 方法下面:

private void webClient_DownloadDataCompleted(object sender, DownloadDataCompletedEventArgs e)
{
    try
    {
        Uri image_url_format = new Uri(image_url);
        byte[] bytes_image = e.Result;
        Stream image_stream = new MemoryStream(bytes_image);
        string dest_folder= Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryDownloads).ToString();
        string file_name= Path.GetFileName(image_url_format.LocalPath);
        string dest_path= Path.Combine(dest_folder, file_name);
        using (var fileStream = new FileStream(dest_path, FileMode.Create, FileAccess.Write))
        {
              image_stream.CopyTo(fileStream);
        }
              DisplayAlert("Alert", "Download completed!", "OK");
    }
    catch (Exception ex)
    {
        DisplayAlert("Error", ex.ToString(), "OK");
    }
}

但它不起作用，没有发现错误，我收到警报，警告我下载已完成.我还允许internet、write_external_storage 和read_external_storage.

But it does not work, no error caught, I get the alert which warn me that the download is completed. Also I gave permission for internet, write_external_storage and read_external_storage.

另一件事是，一段时间后，图像出现在下载相册下的图库中，这是正确的.

Another thing is that the images after some time, appears in the gallery under Download album which is correct.

对这种行为有什么想法吗?

Any idea about this behavior?

编辑

在我的新按钮下载事件下方:

Below my new button download event:

private void button_download_image_Clicked(object sender, EventArgs e)
{

    Uri image_url_format = new Uri(image_url);
    WebClient webClient = new WebClient();
    try
    {
        byte[] bytes_image = webClient.DownloadData(image_url_format);
        Stream image_stream = new MemoryStream(bytes_image);
        string dest_folder = Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryDownloads).ToString();
        string file_name = Path.GetFileName(image_url_format.LocalPath);
        string dest_path = Path.Combine(dest_folder, file_name);
        using (var fileStream = new FileStream(dest_path, FileMode.Create, FileAccess.Write))
        {
            image_stream.CopyTo(fileStream);
        }
    }
    catch (Exception ex)
    {
        DisplayAlert("Error", ex.ToString(), "OK");
    }
    DisplayAlert("Alert", "File scaricato con successo", "OK");
}

推荐答案

图片已正确下载，我可以在我的文件资源管理器中看到它.

The image was downloaded correctly and I can see it in my file explorer.

我通过重新刷新图库解决了我的问题，保存图像后使用此行，因此方法是:

I resolved my problem with a resfresh of the gallery, with this lines after saving my image, so the method will be:

private void button_download_image_Clicked(object sender, EventArgs e)
{
    Uri image_url_format = new Uri(image_url);
    WebClient webClient = new WebClient();
    try
    {
        byte[] bytes_image = webClient.DownloadData(image_url_format);
        Stream image_stream = new MemoryStream(bytes_image);
        string dest_folder = Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryDownloads).ToString();
        string file_name = Path.GetFileName(image_url_format.LocalPath);
        string dest_path = Path.Combine(dest_folder, file_name);
        using (var fileStream = new FileStream(dest_path, FileMode.Create, FileAccess.Write))
        {
            image_stream.CopyTo(fileStream);
        }
        // this 3 lines fix my problem
        var mediaScanIntent = new Intent(Intent.ActionMediaScannerScanFile);
        mediaScanIntent.SetData(Android.Net.Uri.FromFile(new Java.IO.File(dest_path)));
        Android.App.Application.Context.SendBroadcast(mediaScanIntent);
    }
    catch (Exception ex)
    {
        DisplayAlert("Error", ex.ToString(), "OK");
    }
    DisplayAlert("Alert", "File scaricato con successo", "OK");
}

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