c# - Downloading files not affecting UI -

we downloading files using httpclient because our backend requires certificate.

i have control - filerowwhich ui element code-behind methods file downloading, one:

    if (fileisdownloaded == false)     {         await coreapplication.mainview.corewindow.dispatcher.runasync(windows.ui.core.coredispatcherpriority.low, () =>         {             datamanager.instance.downloadfile(this);         });     }     if (thumbnailisdownloaded == false)     {         await coreapplication.mainview.corewindow.dispatcher.runasync(windows.ui.core.coredispatcherpriority.low, () =>         {             datamanager.instance.downloadthumbnail(this);         });     } 

downloading single item fine when click download ( 50 items ) whole ui starts freeze.

as can see, have tried give requests low priority - still same result.

answers common questions:

1) yes files should downloadable @ 1 time, not 1 after another.
2) datamanager.instance.downloadthumbnail(this) - give refference current control report progress in progress bar.

any suggestions?

edit:

downloading looks this:

public async void downloadfile(filerow filerow) {     //lot of checking if file exist, if version same     string localfilename = await downloadmanager.downloadfile(filerow.myfile.file.id, filerow.myfile.file.version, filerow.myfile.file.filename,filerow);     // next using filename string } 

and download:

public static async task<string> downloadfileofcustomerassetrow(int? id, int? version, string filename, filerow filerow)     {         try         {             httpclienthandler ahandler = new httpclienthandler();             ahandler.clientcertificateoptions = clientcertificateoption.automatic;             httpclient aclient = new httpclient(ahandler);             customerassetrow.currentfiledownload = aclient;             aclient.defaultrequestheaders.expectcontinue = false;             httpresponsemessage response = await aclient.getasync(webservices.backendstarturl + "getfiledata?id=" + id + "&version=" + version, httpcompletionoption.responseheadersread);             var file = await applicationdata.current.localfolder.createfileasync(filename, windows.storage.creationcollisionoption.generateuniquename);             filerow.filename = file.name;             using (var fs = await file.openasync(windows.storage.fileaccessmode.readwrite))             {                 stream stream = await response.content.readasstreamasync();                 iinputstream inputstream = stream.asinputstream();                 ulong totalbytesread = 0;                 while (true)                 {                     ibuffer buffer = new windows.storage.streams.buffer(1024);                     buffer = await inputstream.readasync(                         buffer,                         buffer.capacity,                         inputstreamoptions.none);                     if (buffer.length == 0)                     {                         break;                     }                     totalbytesread += buffer.length;                     filerow.progress.value = filerow.progress.value + 1024;                     await fs.writeasync(buffer);                 }                 inputstream.dispose();             }             filerow.progress.visibility = visibility.collapsed;             return file.name;         }         catch (exception e)         {             errorreporter.reporterror("error in downloadmanager.cs in function downloadfile.", e);             return "";         }     } 

it's possible async method continuations interrupting ui thread much. try creating stronger separation between background logic (downloadfileofcustomerassetrow) , ui (filerow) introducing iprogress<t> reporter. ensure every await in background logic has configureawait(false) on it.

public static async task<string> downloadfileofcustomerassetrow(int? id, int? version, string filename, iprogress<int> progress) {     httpclienthandler ahandler = new httpclienthandler();     ahandler.clientcertificateoptions = clientcertificateoption.automatic;     httpclient aclient = new httpclient(ahandler);     customerassetrow.currentfiledownload = aclient;     aclient.defaultrequestheaders.expectcontinue = false;     httpresponsemessage response = await aclient.getasync(webservices.backendstarturl + "getfiledata?id=" + id + "&version=" + version, httpcompletionoption.responseheadersread).configureawait(false);     var file = await applicationdata.current.localfolder.createfileasync(filename, windows.storage.creationcollisionoption.generateuniquename).configureawait(false);     filerow.filename = file.name;     using (var fs = await file.openasync(windows.storage.fileaccessmode.readwrite).configureawait(false))     {         stream stream = await response.content.readasstreamasync().configureawait(false);         iinputstream inputstream = stream.asinputstream();         ulong totalbytesread = 0;         while (true)         {             ibuffer buffer = new windows.storage.streams.buffer(1024);             buffer = await inputstream.readasync(                 buffer,                 buffer.capacity,                 inputstreamoptions.none).configureawait(false);             if (buffer.length == 0)             {                 break;             }             totalbytesread += buffer.length;             if (progress != null)                 progress.report(totalbytesread);             await fs.writeasync(buffer).configureawait(false);         }         inputstream.dispose();     }     return file.name; }