I have following two methods. When user clicks on start button from ui, the step geoLocator_PositionChanged in geoLocator_PositionChanged method is fired and calls the other method geoLocator_PositionChanged.But when it comes to try block while executing the first statement it throws the following error:
"The application called an interface that was marshalled for a different thread. (Exception from HRESULT: 0x8001010E (RPC_E_WRONG_THREAD))"
private async void btnStartStop_Click_1(object sender, RoutedEventArgs e)
{
geoLocator.PositionChanged += geoLocator_PositionChanged;
}
async void geoLocator_PositionChanged(Geolocator sender, PositionChangedEventArgs args)
{
MessageDialog msgdlg = null;
bool bDisplayDialog = false;
try
{
lblAltValue.Text = args.Position.Coordinate.Altitude.ToString();
}
catch
{
}
}
Any help how can I fix this issue ?
You try to access the UI-Thread from another one.
Try something like ths
Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync
(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
{
//HERE GOES THE UI ACCESS LIKE this.textbox.text = "MY AWESOME TEXT";
});
Related
I am firing the following event in my Xamarin application:
AppEvents.Instance.UI.RiseSearchStringTypingEvent(this, new EventArgs());
The HomePage.xaml.cs codebehind subscriber-event performs an auto scroll to top every time the event is being fired (on every input on the search field)
void OnSearchStringTyping(object sender, EventArgs e)
{
scrollView.ScrollToAsync(0.0, 0.0, true);
}
when the searchstring is complete and the user hits the submit-button, the Oncompleted() method invokes on the SearchHeaderView.xaml.cs which navigates to the SearchPage
void OnCompleted(object sender, EventArgs e)
{
var tag = this + ".OnCompleted";
try
{
if (string.Compare(LastSearchText, SearchEntry.Text) == 0) return
if (Device.RuntimePlatform == Device.Android)
{
SearchRequest();
}
else if (Device.RuntimePlatform == Device.iOS)
{
var task = new Task(SearchRequest);
task.Start();
}
LastSearchText = SearchEntry.Text;
}
catch (Exception ex)
{
Track.Exception(tag, ex);
}
}
This procedure works perfect on iOS platforms...But in android, when i submit my search string, the app crashes with an ObjectDisposedException on the ScrollView
I think the problem is that the application tries to scroll up the view again after it navigates away from the homepage. The SearchRequest() method on Android is not invoked in a new Thread, but iOS is. How can i fix this? I can not just make the method being invoked asynchronously, because the Search doesn't work then.
Am I opening the camera for taking a picture, but the user has the possibility to stop the camera if he no longer wants to capture something, so I have a close button which is intended to close the camera, so that the camera preview should be stopped.
If I open the camera, close, open again, I will get the following exception once the close button is clicked for the second time:
System.Runtime.InteropServices.COMException: 'The video recording device is preempted by another immersive application.
I do not know, how the preview camera should be stopped, more than UWP docs say here: https://learn.microsoft.com/en-us/windows/uwp/audio-video-camera/simple-camera-preview-access
The code for stopping the camera preview:
private async Task CleanupCameraAsync()
{
if (_mediaCapture != null)
{
if (_isPreviewing)
{
await _mediaCapture.StopPreviewAsync();
}
await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
CameraPreviewControl.Source = null;
if (_displayRequest != null)
{
_displayRequest.RequestRelease();
}
_mediaCapture.Dispose();
});
}
}
I tried to test your code snippet on my side and it can work well. I didn't get the above exception. I tested on the emulator build 15063 and build 14393. Since your code snippet is not the completed code, so I created a minimal project for testing as follows which can work well on my side. You may test it on your side and compare with your code if something wrong with your project.
XAML
<StackPanel Background="{ThemeResource ApplicationPageBackgroundThemeBrush}" Padding="30">
<CaptureElement Name="PreviewControl" Stretch="Uniform"/>
<Button x:Name="btnpreview" Click="btnpreview_Click" Content="preview test"></Button>
<Button x:Name="btnstop" Click="btnstop_Click" Content="stop"></Button>
</StackPanel>
Code behind
private DeviceInformation _cameraDevice;
private MediaCapture _mediaCapture;
private InMemoryRandomAccessStream _ras;
private LowLagMediaRecording _recording;
private CameraRotationHelper _rotationHelper;
private readonly DisplayRequest _displayRequest = new DisplayRequest();
private bool _isPreviewing;
public MainPage()
{
this.InitializeComponent();
}
private async void btnstop_Click(object sender, RoutedEventArgs e)
{
if (_mediaCapture != null)
{
if (_isPreviewing)
{
await _mediaCapture.StopPreviewAsync();
_isPreviewing = false;
await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
PreviewControl.Source = null;
if (_displayRequest != null)
{
_displayRequest.RequestRelease();
}
_mediaCapture.Dispose();
});
}
}
}
private async void btnpreview_Click(object sender, RoutedEventArgs e)
{
try
{
_mediaCapture = new MediaCapture();
var allVideoDevices = await DeviceInformation.FindAllAsync(DeviceClass.VideoCapture);
var desiredDevice = allVideoDevices.FirstOrDefault(x => x.EnclosureLocation != null && x.EnclosureLocation.Panel == Windows.Devices.Enumeration.Panel.Back);
_cameraDevice = desiredDevice ?? allVideoDevices.FirstOrDefault();
_rotationHelper = new CameraRotationHelper(_cameraDevice.EnclosureLocation);
_mediaCapture.Failed += MediaCapture_Failed;
var settings = new MediaCaptureInitializationSettings { VideoDeviceId = _cameraDevice.Id };
await _mediaCapture.InitializeAsync(settings);
PreviewControl.Source = _mediaCapture;
_displayRequest.RequestActive();
await _mediaCapture.StartPreviewAsync();
_isPreviewing = true;
}
catch (UnauthorizedAccessException)
{
// This will be thrown if the user denied access to the camera in privacy settings
System.Diagnostics.Debug.WriteLine("The app was denied access to the camera");
}
catch (Exception ex)
{
System.Diagnostics.Debug.WriteLine("MediaCapture initialization failed. {0}", ex.Message);
}
}
If you still have issues, please provide a minimal reproduced project and the testing environment information. More details please reference the official sample.
I'm trying to call a MessageDialog out of a PropertyChanged Handler. The first call is always successful, but when the Dialog gets called a second time, I get an UnauthorizedAccessException.
I've tried to wrap the call in a Dispatcher, but I got the same behavior.
Here's the code (snippet of MainPage.xaml.cs):
void PropertyChanged(object sender, PropertyChangedEventArgs e)
{
await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
{
showMessage("Message", "Title");
});
}
async void showMessage(String message, String title)
{
MessageDialog dialog = new MessageDialog(message, title);
await dialog.ShowAsync();
}
Could anybody please help me with this issue?
I think your problem is that multiple property changes will cause multiple calls to display the dialog. You should only ever display one dialog at a time:
bool _isShown = false;
async void showMessage(String message, String title)
{
if (_isShown == false)
{
_isShown = true;
MessageDialog dialog = new MessageDialog(message, title);
await dialog.ShowAsync();
_isShown = false;
}
}
For some reason unhandled exception which occur at non-UI thread don't handled by App_UnhandledException handler.
This approach works well for Windows Phone apps to globally handle, track and analyze exceptions but doesn't work for Windows 8 apps.
this.UnhandledException += App_UnhandledException; //doesn't handle
private void Button_Click_1(object sender, RoutedEventArgs e)
{
var task = new Task(() => { throw new NullReferenceException("Test exc in UI thread"); });
task.Start();
}
Please, advise.
Using the UnobservedTaskException event of TaskScheduler you can catch all exceptions in Tasks that are not awaited. Just to clarify: If you await tasks exceptions are propagated to the UI thread and can hence be catched via Application.UnhandledException.
Using the new async/await keywords:
private async void Button_Click_1(object sender, RoutedEventArgs e)
{
var task = new Task(() => { throw new NullReferenceException("Test exc in UI thread"); });
task.Start();
try
{
await task;
}
catch (Exception ex)
{
var msg = new MessageDialog(ex.ToString(), "An error has occurred");
await msg.ShowAsync();
}
}
Using just the Task methods:
private void Button_Click_1(object sender, RoutedEventArgs e)
{
var task = new Task(() => { throw new NullReferenceException("Test exc in UI thread"); });
task.ContinueWith(t =>
{
var msg = new MessageDialog(t.Exception.ToString(), "An error has occurred");
msg.ShowAsync().Start();
}, TaskContinuationOptions.OnlyOnFaulted);
task.Start();
}
For catching all unhandled exceptions, see this question:
How do I add a Global Exception handler to a Metro Style App?
I have just started building a app using “XihSolutions.DotMSN.dll” version: 2.0.0.40909,
My problem is that it is not firing the “Nameserver_SignedIn” event. Not sure if I am doing something wrong.
your help will be really helpful.
void Nameserver_SignedIn(object sender, EventArgs e)
{
throw new Exception("User Signed In");
}
private string message = string.Empty;
void NameserverProcessor_ConnectionEstablished(object sender, EventArgs e)
{
message = "Connected";
SetMessage();
}
void SetMessage()
{
if (tbMessage.InvokeRequired)
tbMessage. Invoke(new ThreadStart(SetMessage));
else
tbMessage.Text += Environment.NewLine+ message;
}
private void btnSingIn_Click(object sender, EventArgs e)
{
if (messenger.Connected)
{
// SetStatus("Disconnecting from server");
messenger.Disconnect();
}
// set the credentials, this is ofcourse something every DotMSN program will need to
// implement.
messenger.Credentials.Account = tbUserName.Text;
messenger.Credentials.Password = tbPwd.Text;
// inform the user what is happening and try to connecto to the messenger network.
//SetStatus("Connecting to server");
messenger.Connect();
}
You might use MSNPSharp instead - DotMSN is old and may not support the current MSN protocol. There link is here:
http://code.google.com/p/msnp-sharp/