I'm building a WP8 application that changes the background of the lockscreen using images from the Internet. I followed the tutorials over Scheduled Agents and Lockscreen, but I have a problem.
When I try to download the new background image from the Scheduled Agent, i get this:
+ $exception {System.UnauthorizedAccessException: Invalid cross-thread access.
at MS.Internal.XcpImports.CheckThread()
at System.Windows.DependencyObject..ctor(UInt32 nativeTypeIndex, IntPtr constructDO)
at System.Windows.Media.Imaging.BitmapImage..ctor()
at TileLockAgent.ScheduledAgent.lockScreenClient_OpenReadCompleted(Object sender, OpenReadCompletedEventArgs e)
at System.Net.WebClient.OnOpenReadCompleted(OpenReadCompletedEventArgs e)
at System.Net.WebClient.OpenReadOperationCompleted(Object arg)
at System.Threading.WaitCallback.Invoke(Object state)
at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
at System.Threading.ThreadPoolWorkQueue.Dispatch()
at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()} System.Exception {System.UnauthorizedAccessException}
The code is:
string fileName;
try
{
var currentImage = LockScreen.GetImageUri();
if (currentImage.ToString().EndsWith("_1.jpg"))
{
fileName = "LockBackground_2.jpg";
}
else
{
fileName = "LockBackground_1.jpg";
}
}
catch
{
// lockscreen not set or prev owned by other app
fileName = "LiveLockBackground_1.jpg";
}
using (var isoStore = IsolatedStorageFile.GetUserStoreForApplication())
{
var bi = new BitmapImage();
bi.SetSource(e.Result);
var wb = new WriteableBitmap(bi);
using (var isoFileStream = isoStore.CreateFile(fileName))
{
var width = wb.PixelWidth;
var height = wb.PixelHeight;
Extensions.SaveJpeg(wb, isoFileStream, width, height, 0, 100);
}
}
I really don't know how to solve this. How can I save an image in a scheduled agent if BitmapImage is not working? What does it mean that i'm doing "cross-thread access"? The images are created and used only by the scheduled agent, so no one should be accessing them.