I am trying to download image from Internet using async call like this:
private void DoGetAlbumart(object sender, DoWorkEventArgs e)
{
string req = (string)e.Argument;
WebClient wc = new WebClient();
wc.OpenReadCompleted += new OpenReadCompletedEventHandler(ReadWebRequestCallback);
wc.OpenReadAsync(new Uri(req));
}
void ReadWebRequestCallback( object sender, OpenReadCompletedEventArgs e)
{
if (e.Error == null && !e.Cancelled)
{
try
{
BitmapImage image = new BitmapImage();
image.SetSource(e.Result);
SecondTile.Source = image;
}
catch (Exception ex)
{
}
}
else
{
}
}
It seems that when breakpoint hits at BitmapImage image = new BitmapImage(), I got the following exception:
ex = {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()
What else can I try to get rid of this error?
Callback methods run in background threads, not the UI thread. Unfortunately, BitmapImages can only be instantiated in the UI thread. If you need to access the UI thread from a callback, try the following:
Deployment.Current.Dispatcher.BeginInvoke(() =>
{
BitmapImage image = new BitmapImage();
image.SetSource(e.Result);
SecondTile.Source = image;
});
Related
I am following this sample to implement a background server universal app. Here is the experimental code:
void MainPage::OnConnectionReceived(StreamSocketListener^ sender, StreamSocketListenerConnectionReceivedEventArgs^ args)
{
OutputDebugString(L"Connection received\n");
// No idea how to transfer request handling from foreground to background task!
}
void MainPage::OnNavigatedTo(NavigationEventArgs^ e)
{
// Code to register background task is omitted
auto listener = ref new StreamSocketListener();
listener->Control->QualityOfService = SocketQualityOfService::Normal;
try
{
listener->EnableTransferOwnership(Task->TaskId, SocketActivityConnectedStandbyAction::Wake);
}
catch (...)
{
OutputDebugString(L"Error: cannot transfer ownership\n");
}
listener->ConnectionReceived += ref new TypedEventHandler<StreamSocketListener^, StreamSocketListenerConnectionReceivedEventArgs^>(this, &MainPage::OnConnectionReceived);
create_task(listener->BindServiceNameAsync("56789", SocketProtectionLevel::PlainSocket))
.then([this]()
{
OutputDebugString(L"Server started on port 56789\n");
auto m_httpClient = ref new HttpClient();
auto request = ref new HttpRequestMessage(HttpMethod::Get, ref new Uri("http://" + ip + ":56789/"));
auto request_operation = m_httpClient->SendRequestAsync(request, HttpCompletionOption::ResponseContentRead);
return create_task(request_operation);
}).then([this](task<HttpResponseMessage^> previousTask)
{
try {
auto response = previousTask.get();
// Code to process the response is omitted as it is irrelevant to the question
}
catch (Exception^ ex)
{
OutputDebugString(("Error: " + ex->Message + "\n")->Data());
}
});
}
At run time, I get the error: The attempted operation is not supported for the type of object referenced. which suggests that BindServiceNameAsync fails and I have no idea why as I have followed the documentation to do EnableTransferOwnership before doing the binding. What did I do wrong here?
You are getting The attempted operation is not supported for the type of object referenced. because you are using SocketActivityConnectedStandbyAction::Wake. Change it to SocketActivityConnectedStandbyAction::DoNotWake.
The following pseudo-code should give you an idea what else you need to do to make StreamSocketListener working with SocketActivityTrigger:
// TODO: task = socketTaskBuilder.Register();
socketListener = new StreamSocketListener();
socketListener.ConnectionReceived += OnConnected;
await socketListener.BindServiceNameAsync(port);
socketListener.EnableTransferOwnership(
task.TaskId,
SocketActivityConnectedStandbyAction.DoNotWake);
// This is required, otherwise you may get error:
// A device attached to the system is not functioning.
// (Exception from HRESULT: 0x8007001F)
await socketListener.CancelIOAsync();
socketListener.TransferOwnership(socketId);
Then, in the background task do:
public async void Run(IBackgroundTaskInstance taskInstance)
{
var deferral = taskInstance.GetDeferral();
var details = taskInstance.TriggerDetails as
SocketActivityTriggerDetails;
var socketInformation = details.SocketInformation;
var streamSocket = socketInformation.StreamSocket;
var socketListener = socketInformation.StreamSocketListener;
switch (details.Reason)
{
case SocketActivityTriggerReason.ConnectionAccepted:
// TODO: read, write, etc.
break;
default:
// ...
break;
}
// ...
deferral.Complete();
}
I'm trying to create an app that can use the camera for Windows Phone 8.1, using the Windows RT/XAML development model.
When I try to call either of the capture methods off of the MediaCapture class I get an ArgumentException with the message "The parameter is incorrect." Here is my code
private async Task Initialize()
{
if (!DesignMode.DesignModeEnabled)
{
await _mediaCaptureMgr.InitializeAsync();
ViewFinder.Source = _mediaCaptureMgr;
await _mediaCaptureMgr.StartPreviewAsync();
}
}
private async void ViewFinder_OnTapped(object sender, TappedRoutedEventArgs e)
{
ImageEncodingProperties imageProperties = ImageEncodingProperties.CreateJpeg();
var stream = new InMemoryRandomAccessStream();
await _mediaCaptureMgr.CapturePhotoToStreamAsync(imageProperties, stream);
_bitmap = new WriteableBitmap((int) ViewFinder.ActualWidth, (int) ViewFinder.ActualHeight);
stream.Seek(0);
await _bitmap.SetSourceAsync(stream);
PreviewImage.Source = _bitmap;
PreviewElements.Visibility = Visibility.Visible;
ViewFinder.Visibility = Visibility.Collapsed;
Buttons.Visibility = Visibility.Visible;
Message.Visibility = Visibility.Collapsed;
stream.Seek(0);
var buffer = new global::Windows.Storage.Streams.Buffer((uint) stream.Size);
stream.ReadAsync(buffer, (uint) stream.Size, InputStreamOptions.None);
DataContext = buffer.ToArray();
if (PhotoCaptured != null)
PhotoCaptured(this, null);
}
The initialize method is called on page load, and the viewfinder_ontapped is called when they tap the CaptureElement I have in the xaml. The error is thrown on
await _mediaCaptureMgr.CapturePhotoToStreamAsync(imageProperties, stream);
What's really bizarre is that I downloaded the latest source for the winrt xaml toolkit http://winrtxamltoolkit.codeplex.com/ and tried their sample camera app, which uses similar code. It throws the same error on MediaCapture.CapturePhotoToStorageFileAsync(). Can anyone help me identify why?
I am working on a Windows Universal App. I Want to get the Data from a Bluetooth Device to the Windows Phone. I am Using the Concept of RFCommCommunicationTrigger for this Purpose.
Here's the code Snippet I am Using
var rfTrigger = new RfcommConnectionTrigger();
// Specify what the service ID is
rfTrigger.InboundConnection.LocalServiceId = RfcommServiceId.FromUuid(new Guid("<some_base_guid>"));
//Register RFComm trigger
var rfReg = RegisterTaskOnce(
"HWRFCommTrigger",
"BackgroundLibrary.RFBackgroundTask",
rfTrigger, null
);
SetCompletedOnce(rfReg, OnTaskCompleted);
Here the Function of RegisterTaskOnce
static private IBackgroundTaskRegistration RegisterTaskOnce(string taskName, string entryPoint, IBackgroundTrigger trigger, params IBackgroundCondition[] conditions)
{
// Validate
if (string.IsNullOrEmpty(taskName)) throw new ArgumentException("taskName");
if (string.IsNullOrEmpty(entryPoint)) throw new ArgumentException("entryPoint");
if (trigger == null) throw new ArgumentNullException("trigger");
// Look to see if the name is already registered
var existingReg = (from reg in BackgroundTaskRegistration.AllTasks
where reg.Value.Name == taskName
select reg.Value).FirstOrDefault();
Debug.WriteLine("Background task "+ taskName+" is already running in the Background");
// If already registered, just return the existing registration
if (existingReg != null)
{
return existingReg;
}
// Create the builder
var builder = new BackgroundTaskBuilder();
builder.TaskEntryPoint = entryPoint;
builder.Name = taskName;
builder.SetTrigger(trigger);
// Conditions?
if (conditions != null)
{
foreach (var condition in conditions)
{
builder.AddCondition(condition);
}
}
// Register
return builder.Register();
}
Here's the code for SetCompletedOnce this will add a Handler only once
static private void SetCompletedOnce(IBackgroundTaskRegistration reg, BackgroundTaskCompletedEventHandler handler)
{
// Validate
if (reg == null) throw new ArgumentNullException("reg");
if (handler == null) throw new ArgumentNullException("handler");
// Unsubscribe in case already subscribed
reg.Completed -= handler;
// Subscribe
reg.Completed += handler;
}
I have also Written the BackgroundLibrary.RFBackgroundTask.cs
public sealed class RFBackgroundTask : IBackgroundTask
{
public async void Run(IBackgroundTaskInstance taskInstance)
{
BackgroundTaskDeferral deferral = taskInstance.GetDeferral();
try
{
Debug.WriteLine(taskInstance.TriggerDetails.GetType());
taskInstance.Canceled += new BackgroundTaskCanceledEventHandler(OnCanceled);
Debug.WriteLine("RFComm Task Running");
Debug.WriteLine(taskInstance.TriggerDetails.GetType().ToString());
}
catch (System.Exception e)
{
Debug.WriteLine("RFComm Task Error: {0}", e.Message);
}
deferral.Complete();
}
}
The Run Method is Invoked Every Time The Device tries to Open the Connection.
The type of the Trigger that is obtained (the type I am debugging in the run method of the RFBackgroundTask.cs) is printed as
Windows.Devices.Bluetooth.Background.RfcommConnectionTriggerDetails
But I am Unable use that because I dont have this Class in the BackgroundLibrary project.
The Documentation says that this Provides information about the Bluetooth device that caused this trigger to fire.
It has Variables like Socket,RemoteDevice etc.
I think I am Missing something very simple
Can you please help me out .
Once your background task is launched, simply cast the TriggerDetails object to an RfcommConnectionTriggerDetails object:
public sealed class RFBackgroundTask : IBackgroundTask
{
public async void Run(IBackgroundTaskInstance taskInstance)
{
BackgroundTaskDeferral deferral = taskInstance.GetDeferral();
try
{
taskInstance.Canceled += new BackgroundTaskCanceledEventHandler(OnCanceled);
RfcommConnectionTriggerDetails details = (RfcommConnectionTriggerDetails)taskInstance.TriggerDetails;
StreamSocket = details.Socket; // Rfcomm Socket
// Access other properties...
}
catch (System.Exception e)
{
Debug.WriteLine("RFComm Task Error: {0}", e.Message);
}
deferral.Complete();
}
}
I have another question about a "JDWP Error: 21" logged: Unexpected JDWP Error 21
I am trying to parse some XML I gather from a servlet into a J2ME MIDlet with the code below. So far unsuccessfully, I think due to the JDWP error on my HttpConnection how ever the InputStream is filled with XML and once parsed everything inside the Document is null.
Has anyone got and ideas about the JDWP error, and also does that code look like it should work?
In MIDlet I am using JSR-172 API javax.xml.parsers.*.
if(d==form1 && c==okCommand)
{
// Display Webpage
webPage = new TextBox(txtField.getString(),
"",
100000,
TextField.ANY
);
Display.getDisplay(this).setCurrent(webPage);
try
{
HttpConnection conn = (HttpConnection)Connector.open("http://localhost:8080/Blogging_Home/Interface?Page=Bloggers&Action=VIEW&Type=XML");
conn.setRequestMethod(HttpConnection.GET);
int rc = conn.getResponseCode();
getConnectionInformation(conn, webPage);
webPage.setString(webPage.getString() + "Starting....");
String methodString = getStringFromURL("");
if (rc == HttpConnection.HTTP_OK)
{
InputStream is = null;
is = createInputStream(methodString);
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder;
Document document;
try
{
builder = factory.newDocumentBuilder();
document = builder.parse(is);
} catch (Exception e) {
e.printStackTrace();
}
}
else
{
webPage.setString(webPage.getString() + "ERROR:" + rc);
}
}
catch(Exception ex)
{
// Handle here
webPage.setString("Error" + ex.toString());
}
I have problems reading from my MSMQ. When I write to the queue, it works perfectly, but when I try to read that message from the queue, I get the following exception: "The queue does not exist or you do not have sufficient permissions to perform the operation." The queue does exists, and I have full permissions on the machine and queue. Here is my code:
public string path = #".\private$\";
public void WriteToQueue(string QueueName, object messageObject)
{
try
{
path = path + QueueName;
MessageQueue msmq = null;
if (!MessageQueue.Exists(path))
{
msmq = MessageQueue.Create(path);
}
else
{
msmq = new MessageQueue(path);
}
msmq.Formatter = new XmlMessageFormatter(new Type[] { typeof(string)});
msmq.Send(messageObject);
msmq.Close();
}
catch (MessageQueueException ex)
{
System.ArgumentException argEx = neArgumentException(ex.ToString());
throw argEx;
}
path = #".\private$\";
}
public string ReadQueue(string QueueName)
{
try
{
path = path + QueueName;
MessageQueue msmq = new MessageQueue(path);
string msg;
msmq.Formatter = new XmlMessageFormatter(new Type[] { typeof(string)});
msg = msmq.Receive().Body.ToString(); //exception is thrown here
path = #".\private$\";
return msg;
}
catch (Exception ex)
{
return null;
}
}
can the problem maybe be with reading it as type of string? Maybe not in the right format?
Try this:
public string path = ".\\private$\\";
'#' doesn't work for me too.