异步方法挂起UI

Question

I have a window, which uses some async methods. However, it only hangs UI (during these operations) only if i create it on runtime, like this:

private void button_Click(object sender, RibbonControlEventArgs e)
{
    AboutWindow SettingsWindow = new AboutWindow();
    SettingsWindow.ShowDialog();
}

However, if I create it like this:

private AboutWindow SettingsWindow = new AboutWindow();
private void button_Click(object sender, RibbonControlEventArgs e)
{
    SettingsWindow.ShowDialog();
}

Everything seems to be OK and UI is not hanging.

The methods inside the window, that cause the problems are presented below:

private async void CallUpdateDownload()
{
    UpdaterStatus.CurrentUpdateStatus = await DownloadAndSaveInstallerAsync(UpdaterStatus.freshVersion);
}

public static async Task<UpdateStatus> DownloadAndSaveInstallerAsync(string NewVersion)

The main hang occurs on this string inside DownloadAndSaveInstallerAsync :

CloudBlockBlob blob = new CloudBlockBlob(new Uri(sas));
MemoryStream msRead = new MemoryStream();
blob.DownloadToStream(msRead); // HANGS HERE

The question is , why this happens? Why creating the window on start prevents it from hanging from async methods.

The other question is , that I have another object, which also uses DownloadAndSaveInstallerAsync method. These objects are created on runtime, and I can't do anything to prevent this hanging, occuring on download.

How can I prevent UI from hanging in this situation (creating objects on runtime)?

More code below:

        private async void CallUpdateDownload()
                {
                    UpdaterStatus.CurrentUpdateStatus = await UpdaterLogic.DownloadAndSaveInstallerAsync(UpdaterStatus.freshVersion);
                }

UpdaterLogic:

        public static async Task<UpdateStatus> DownloadAndSaveInstallerAsync(string NewVersion)
                {
        //...
                          if (await SaveInstallerToMemoryAsync(NewVersion))
                                {
                                        return UpdateStatus.ReadyToInstall;
                                }
                                else
                                {
                                    return UpdateStatus.Error;
                                }
                }

    private static async Task<bool> SaveInstallerToMemoryAsync(string NewVersion)
            {
                        using (MemoryStream ms = await UpdaterClient.DownloadInstallerAsync(NewVersion))
                        using (FileStream fs = new FileStream(UpdaterSettings.Path), FileMode.Create))
                        {
                            if (ms == null) return false;
                            ms.Position = 0;
                            await ms.CopyToAsync(fs);
                            fs.Close();
                            ms.Close();
                            return true;
                        }
            }

UpdaterClient:

    public static async Task<MemoryStream> DownloadInstallerAsync(string version)
            {
                        string sas = await GetInstallerDownloadLinkAsync(version);

                        CloudBlockBlob blob = new CloudBlockBlob(new Uri(sas));

                            MemoryStream msRead = new MemoryStream();
                            blob.DownloadToStream(msRead);
                            return msRead;
            }

public static async Task<string> GetInstallerDownloadLinkAsync(string version)
        { 
                    HttpResponseMessage response = null;
                        response = await httpClient.GetAsync(UpdaterSettings.Link + version);
                    if (response.IsSuccessStatusCode)
                    {
                        var res = await response.Content.ReadAsStringAsync();
                        return res.Trim('"');
                    }
        }

Answer 1

You have to execute the long running parts inside a task/thread and await them to avoid blocking.

public static async Task<MemoryStream> DownloadInstallerAsync(string version)
{
    string sas = await GetInstallerDownloadLinkAsync(version);

    CloudBlockBlob blob = new CloudBlockBlob(new Uri(sas));

    MemoryStream msRead = new MemoryStream();
    await Task.Run( () => blob.DownloadToStream(msRead) );
    return msRead;
}

Update

CloudBlockBlob does offer an DownloadToStreamAsync method which you can use

public static async Task<MemoryStream> DownloadInstallerAsync(string version)
{
    string sas = await GetInstallerDownloadLinkAsync(version);

    CloudBlockBlob blob = new CloudBlockBlob(new Uri(sas));

    MemoryStream msRead = new MemoryStream();
    await blob.DownloadToStreamAsync(msRead);
    return msRead;
}