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POWindows Phone ScheduleAgent grabbing images on set period
 

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    <p>I'm attempting to follow an <a href="http://developer.nokia.com/Community/Wiki/Dynamic_Lock_Screen_for_Windows_Phone_8" rel="nofollow">Windows Phone tutorial</a>, tweaking it a bit to fit my needs. I am trying to grab a new picture every X seconds (30 for debugging) and set it as the new lockscreen background. I created a ScheduleAgent object to call it, however, it seems to be skipping a function. It <i>does not</i> skip this when in the <code>MainPage.xaml.cs</code>, which runs the exact same function.</p> <p><strong>ScheduleAgent.cs</strong></p> <pre><code> static ScheduledAgent() { ....&lt;irrelevant code&gt;.... protected override void OnInvoke(ScheduledTask task) { .... &lt; Code went here that shouldn't matter &gt; .... } Debug.WriteLine("Imagename = " + imageName); DownloadImagefromServer("https://s3-us-west-2.amazonaws.com/qoutescreen/0" + imageName + ".jpg"); </code></pre> <p>m.ReleaseMutex(); }</p> <pre><code> // If debugging is enabled, launch the agent again in one minute. // debug, so run in every 30 secs #if(DEBUG_AGENT) ScheduledActionService.LaunchForTest(task.Name, TimeSpan.FromSeconds(30)); System.Diagnostics.Debug.WriteLine("Periodic task is started again: " + task.Name); #endif // Call NotifyComplete to let the system know the agent is done working. NotifyComplete(); } //=============================================================================== private async void LockScreenChange(string filePathOfTheImage, bool isAppResource) { if (!LockScreenManager.IsProvidedByCurrentApplication) { // If you're not the provider, this call will prompt the user for permission. // Calling RequestAccessAsync from a background agent is not allowed. await LockScreenManager.RequestAccessAsync(); } // Only do further work if the access is granted. if (LockScreenManager.IsProvidedByCurrentApplication) { // At this stage, the app is the active lock screen background provider. // The following code example shows the new URI schema. // ms-appdata points to the root of the local app data folder. // ms-appx points to the Local app install folder, to reference resources bundled in the XAP package var schema = isAppResource ? "ms-appx:///" : "ms-appdata:///Local/"; var uri = new Uri(schema + filePathOfTheImage, UriKind.Absolute); // Set the lock screen background image. LockScreen.SetImageUri(uri); // Get the URI of the lock screen background image. var currentImage = LockScreen.GetImageUri(); System.Diagnostics.Debug.WriteLine("The new lock screen background image is set to {0}", currentImage.ToString()); } } private async Task DownloadImagefromServer(string imgUrl) { Debug.WriteLine("Attempting to Get Image from Server..."); WebClient client = new WebClient(); try { // I GET A "Cannot await Void" problem here?!?!? //================================================================= var result = await client.OpenReadAsync(new Uri(imgUrl, UriKind.Absolute)); BitmapImage bitmap = new BitmapImage(); bitmap.SetSource(result); return result; } catch (Exception e) { Debug.WriteLine(e); } client.OpenReadCompleted += new OpenReadCompletedEventHandler(client_OpenReadCompleted); //client.OpenReadAsync(new Uri(imgUrl, UriKind.Absolute)); } //------------------------------------------------------------------ //THIS FUNCTION IS NEVER HIT WHEN RUN IN THE ScheduleAgent.cs CODE, HOWEVER // WHEN IT IS RUN INT HE MainPage.xaml.cs CODE (Which is a copy/paste) IT RUNS FINE // WHY IS IT NOT HITTING THIS? HOW CAN I FIX IT? //------------------------------------------------------------------ void client_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e) { BitmapImage bitmap = new BitmapImage(); bitmap.SetSource(e.Result); //img.Source = bitmap; // Create a filename for JPEG file in isolated storage. String tempJPEG = "DownloadedWalleper.jpg"; // Create virtual store and file stream. Check for duplicate tempJPEG files. using (IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile.GetUserStoreForApplication()) { if (myIsolatedStorage.FileExists(tempJPEG)) { myIsolatedStorage.DeleteFile(tempJPEG); } IsolatedStorageFileStream fileStream = myIsolatedStorage.CreateFile(tempJPEG); StreamResourceInfo sri = null; Uri uri = new Uri(tempJPEG, UriKind.Relative); sri = Application.GetResourceStream(uri); //BitmapImage bitmap = new BitmapImage(); //bitmap.SetSource(sri.Stream); WriteableBitmap wb = new WriteableBitmap(bitmap); // Encode WriteableBitmap object to a JPEG stream. Extensions.SaveJpeg(wb, fileStream, wb.PixelWidth, wb.PixelHeight, 0, 85); //wb.SaveJpeg(fileStream, wb.PixelWidth, wb.PixelHeight, 0, 85); fileStream.Close(); } LockScreenChange("DownloadedWalleper.jpg", false); } } </code></pre>
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    1. COThe problem is that `DownloadImagefromServer` is asynchronous, so the method returns before the image is downloaded. Then you call `NotifyComplete`, which stops the execution of your background agent. Use a mutex to prevent the `OnInvoke` method from returning before the file has finished downloading.
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    2. COBut it is skipping the function call completely. So to me, it seems that it doesn't even try, not that it doesn't have enough time. Am I wrong in assuming that?
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    3. COWell, set a breakpoint to be sure, but I don't see why it would skip the call
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