We have a WPF app that also runs on a tablet. We are targeting Windows 10, .Net 4.6.2.
We have an async event handler that calls MessageBox.Show. The user clicks Yes and the app continues on doing some stuff.
When the app runs on tablet hardware, the app locks up for 10-20 seconds after the event completes. I cannot duplicate this from the desktop or in the simulator, only when it actually runs on the tablet.
I have isolated it to the MessageBox. When I take it out the app behaves normally. I feel like maybe it has something to do with threading.
Any ideas?
using "async" will cause the MesssageBox.Show() method to be called on a separate thread. instead of putting the MesssageBox.Show() call in an async call consider putting it in a Thread, ensuring you declare it a background thread:
Thread messageBoxThread = new Thread(() => { yourMessageBoxCall(); );
messageBoxThread.IsBackground = true;
messageBoxThread.Start();
Based on #stuicidle's clue, I went down a better research path. Many people have tried to solve the async MessageBox problem.
I ultimately got my solution from how can i use Messagebox.Show in async method on Windows Phone 8?
My code looks like this:
private async Task HandleEvent()
{
var message = $"Continue?";
MessageBoxResult result = MessageBoxResult.None;
var dg = new Action(() => result = MessageBox.Show(message, "Warning", MessageBoxButton.YesNo));
await Dispatcher.BeginInvoke(dg);
if (result == MessageBoxResult.Yes)
await DoSomeStuff();
}
Related
I have a WPF (MVVM with Prism) application
There are quite a lot of factors that can affect this problem, but I will try to boil it down.
Hopefully I can at least get some tips how to trouble shoot this.
I have a user control containing a datagrid and a typical Search-button. The grid is initially empty and on SearchCommand. The user control uses a class "AccountServiceGateway" (_accountSG below) to make a request to the server, and then fills datasource of the grid with the result. Pretty standard.
VM: Binding command to handler in ctor
...
SearchCommand = new DelegateCommand(async () => await SearchOnServer(new AccountFilterDTO()));
VM, Button handler implementation
private async Task<bool> SearchOnServer(AccountFilterDTO filter)
{
var searchAccountResults = await _accountSG.SearchAccounts(filter);
//AccountSearchResultList is an observable collection that is datasource for the grid
AccountSearchResultList = new ObservableCollection<AccountSearchResultDTO>(searchAccountResults);
}
// Account Service gateway, making a web request
protected async Task<T> GetFromUrl<T>(string urlPart)
{
...
var response = await _httpClient.GetAsync(url);
resStr = await response.Content.ReadAsStringAsync();
//convert to T and return
}
EDIT
When I replace the implementation of GetFromUrl() with
await Task.Delay(5000)
return [hardcoded list of T]
everything works ok (although the hardcoded list is only 5 items)
END EDIT
Now to my problem. Getting an answer from the server taks about 1-2secs, as expected. I can follow the code until my datasource is filled. But then the GUI freezes for roughly (10-)20 seconds before anything is displayed, then efter the freeze, everything is as expected.
Other things to notice is that user control is in a Prism-region, within a Telerik RadTabbedWindow, so if this looks ok ith might be something else.
So my main question is, why does it hang for 20 seconds, I suspect there is some threading problem, but if it where a deadlock, wouldnt it hang forever? Any way to trouble shoot this?
Has the view changed in some way so that list virtualisation has been effectively turned off?
eg. Parent ScrollerViewer been added
I have been slowly trying to convert my code from using action delegates to the new Tasks in my WPF application. I like the fact that an await operation can run in the same method, greatly reducing the number of methods I need, enhancing readability, and reducing maintenance. That being said, I am having a problem with my code when calling EF6 async methods. They all seem to run synchronously and are blocking my UI thread. I use the following technologies/frameworks in my code:
.NET Framework 4.5
WPF
MVVM Light 5.2
Generic Unit Of Work/Repository Framework v3.3.5
https://genericunitofworkandrepositories.codeplex.com/
Entity Framework 6.1.1
SQL Server 2008 R2 Express
As an example, I have a LogInViewModel, with a command that executes after a button is clicked on my WPF application. Here is the command as initialized in the constructor:
LogInCommand = new RelayCommand(() => ExecuteLogInCommand());
Here is the command body:
private async void ExecuteLogInCommand()
{
// Some code to validate user input
var user = await _userService.LogIn(username, password);
// Some code to confirm log in
}
The user service uses a generic repository object that is created using MVVM Light's SimpleIoC container. The LogIn method looks like this:
public async Task<User> LogIn(string username, string password)
{
User user = await _repository.FindUser(username);
if (user != null && user.IsActive)
{
// Some code to verify passwords
return user;
}
return null;
}
And my repository code to log in:
public static async Task<User> FindUser(this IRepositoryAsync<User> repository, string username)
{
return await repository.Queryable().Where(u => u.Username == username).SingleOrDefaultAsync();
}
The SingleOrDefaultAsync() call is Entity Framework's async call. This code is blocking my UI thread. I have read multiple articles from Stephen Cleary and others about async await and proper use. I have tried using ConfigureAwait(false) all the way down, with no luck. I have made my RelayCommand call use the async await keywords with no luck. I have analyzed the code and the line that takes the longest to return is the SingleOrDefaultAsync() line. Everything else happens almost instantaneously. I have the same problem when making other async calls to the DB in my code. The only thing that fixes it right away is the following:
User user = await Task.Run(() =>
{
return _userService.LogIn(Username, p.Password);
});
But I understand this should not be necessary since the call I am making to the database is IO bound and not CPU bound. So, what is wrong with my application and why is it blocking my UI thread?
Your RelayCommand is not async.
LogInCommand = new RelayCommand(() => ExecuteLogInCommand());
Because there is no async/await your ExecuteLogInCommand will be called synchronously.
You got to change it to
LogInCommand = new RelayCommand(async () => await ExecuteLogInCommand());
so that the RelayCommand is called async too.
Your LogIn and FindUser (which, according to the guidelines, should be called LogInAsync and FindUserAsync) which are not supposed to work with the UI should use ConfigureAwait(false) on all awaits.
However all calls are synchronous until something really asynchronous is called. I suppose that would be SingleOrDefaultAsync.
If wrapping it in Task.Run makes such a difference, then, for some reason, SingleOrDefaultAsync must be running synchronously.
When you have a button, and do something like:
Private Function Button_OnClick
Button.Enabled = False
[LONG OPERATION]
End Function
Then the button will not be grayed, because the long operation prevents the UI thread from repainting the control. I know the right design is to start a background thread / dispatcher, but sometimes that's too much hassle for a simple operation.
So how do I force the button to redraw in disabled state? I tried .UpdateLayout() on the Button, but it didn't have any effects. I also tried System.Windows.Forms.DoEvents() which normally works when using WinForms, but it also had no effect.
The following code will do what you're looking for. However I would not use it. Use the BackgroundWorker class for long time operations. It's easy to use and very stable.
Here the code:
public static void ProcessUITasks() {
DispatcherFrame frame = new DispatcherFrame();
Dispatcher.CurrentDispatcher.BeginInvoke(DispatcherPriority.Background, new DispatcherOperationCallback(delegate(object parameter) {
frame.Continue = false;
return null;
}), null);
Dispatcher.PushFrame(frame);
}
Here you will find a sample on how to use the BackgroundWorker.
InvalidateVisual(); #HCL is right... don't do this
Like you say, it is better to start use a background thread / dispatcher and keep the UI thread unblocked. Consider looking at the Reactive Extensions library from Microsoft for high level asynchronous ui programming
In Windows.Forms, you can Button.Refresh().
In Windows.Forms or WPF, you can yield to the message pump to let it redraw. Async/Await were designed to allow you to do this without the nastiness of HCL's answer.
Private Async Function Button_OnClick
Button.Enabled = False
Await Task.Yield
[LONG OPERATION]
End Function
I try to delay close a window in my App.xaml.ca :
Window splash = new Window();
splash.Show();
Timer timer = new Timer(callback, null, 2000, Timeout.Infinite);
private void callback(object stateInfo)
{
splash.Close();
}
It works fine, but the whole App is shutdowning. What am doing wrong here ?
Be sure to check that you timer callback is coming back on the main dispatcher thread. If not then you will likely be getting an exception when you try to close your window from a different thread.
Use splash.Dispatcher.CheckAccess() to make sure you are on the right thread and if not then use splash.Dispatcher.BeginInvoke((Action) () => splash.Close() to dispatch the call onto the main thread.
Check out this page for more
Here is my solution to this exact same problem:
private async void CloseWindow()
{
await ClosingTasks();
}
private async Task ClosingTasks()
{
await Task.Delay(2000);
this.Close();
}
Where you simply call CloseWindow() when you want to close the current window after the given delay of 2000 mS.
There are different shutdown modes, if that window is closed and it is the last then the application will shut down by default. So you can either see to it that there is still some window around or you can change the shutdown behaviour by setting the ShutdownMode to something that suits your needs.
e.g.
Application.Current.ShutdownMode = System.Windows.ShutdownMode.OnExplicitShutdown;
I'm trying to put standard output from nmap into WPF window application (textbox exactly). I'm trying to use Dispatcher.Invoke but when nmap process starts everything just freezes. When I tried this in a console application (w/o Invoke), everything worked just fine, I think it's a problem with the Invoke method. Nmap itself is working, and finishing it work, but there is no response in my window.
Here's the code I'm using:
Process nmap = new Process();
nmap.StartInfo.FileName = Properties.Settings.Default.NmapResidentialPath;
nmap.StartInfo.Arguments = arguments.ToString();
nmap.StartInfo.UseShellExecute = false;
nmap.StartInfo.RedirectStandardOutput = true;
nmap.OutputDataReceived += new DataReceivedEventHandler(nmap_OutputDataReceived);
nmap.Start();
nmap.BeginOutputReadLine();
nmap.WaitForExit();
nmap.Close();
And the event handler method:
void nmap_OutputDataReceived(object sender, DataReceivedEventArgs e)
{
if (!String.IsNullOrEmpty(e.Data))
{
this.Dispatcher.Invoke(DispatcherPriority.Normal, (Action)(() => nmapOutput.Text += "\n" + e.Data));
}
}
This may be caused by various reasons.
First, Ensure that nmapOutput control is created on UI Thread.
Second, Dispatcher.Invoke may cause UI Thread deadlock (and it probably is in your case).
Always call Dispatcher.CheckAccess() before calling Invoke, or use BeginInvoke to perform this operation in async manner.