Call from DLL (Window Runtime component)

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I have a store application where I am using a control from DLL (Based on Window Runtime component). My all View Models are in that DLL. In that DLL there is timer which updates the view (UI) and get exception "Called from different thread". I am not sure how to resolve this proble.

Posted 25-Dec-13 9:45am

AghaKhan

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AghaKhan 26-Dec-13 0:28am

C# Window store Application

2 solutions

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Sergey Alexandrovich Kryukov · Answer 1 · 2013-12-25T10:17:00

Solution 1

The problem is totally unrelated to DLL, it is related to the use of the threading with UI. The timer even is not guaranteed to be invoked on the same thread, that's the problem.

You cannot call any method or property of the currently executing UI from any thread other then UI thread. For solving such problems, there is the method CoreDispatcher.RunAsync. It queues some callback with the parameters needed for the call to the UI thread; eventually, you call will be performed by the UI thread. This is the way you can notify the UI thread from other threads. The detail depends on exact language and API you use; please see:
http://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.core.coredispatcher.aspx[^].

—SA

Posted 25-Dec-13 10:17am

Sergey Alexandrovich Kryukov

Updated 25-Dec-13 10:19am

v2

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AghaKhan 25-Dec-13 20:41pm

Thank you kind email. In my solution I am using MVVM design pattern where all the ModelView are in DLL, but I am supplying data to DataContext (ModelViw) from main application. ModelView is creating a timer thread which updates the UI, which try to update the UI and get exception. Now how or where I have to call the CoreDispatcher.RunAsync function. Before your answer I looked http://mikaelkoskinen.net/fixing-coredispatcher-invoke-how-to-invoke-method-in-ui-thread-in-windows-8-release-preview/ and tried to supply ModelView to DLL object with RunAsync function which failed. DLL doesn't know anything about main application and how can (I can't) we update UI thread from DLL? It is a small application and if you want I can send you the application to look at it. Thanks for email.

Best regards
Agha Khan

Sergey Alexandrovich Kryukov 25-Dec-13 23:16pm

What language are you using?
—SA

AghaKhan 26-Dec-13 3:38am

public event PropertyChangedEventHandler PropertyChanged;
private async void NotifyChanged(string propertyName)
{
if (this.PropertyChanged != null)
{
var ignored = await CoreDispatcher.RunAsync(CoreDispatcherPriority.Normal,
() => { PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); });
}
}
Error:
Error 1 An object reference is required for the non-static field, method, or property 'Windows.UI.Core.CoreDispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority, Windows.UI.Core.DispatchedHandler)' C:\Apps\CSharp\Nuts\VisualControls\FlipViewModel.cs 36 37 VisualControls

Sergey Alexandrovich Kryukov 26-Dec-13 12:12pm

What are you doing? RunAsync is not a static method!
You need to use the instance, which is obtained from CodeWindow.Dispatcher property.
—SA

AghaKhan 26-Dec-13 14:22pm

:-) Thank you.

var coreDispatcher = new CoreDispatcher();
The type 'Windows.UI.Core.CoreDispatcher' has no constructors defined
What todo now?
Thanks for help.

Sergey Alexandrovich Kryukov 26-Dec-13 14:49pm

Of course it does not. I already told you what to do.
Look, do you understand abstract vs non-abstract classes, types vs instances and static vs instance (non-static) members? Accessibility? "this"? Mechanism of passing instance references? Reference vs value types? Compile-time vs runtime types? Your follow-up questions show that you don't. Really sorry about it.

Here is what I can advise. Stop using store API, threads and doing ant other advanced development for a while. You really need to learn basics first. Take a manual, read it all without skipping, do simple exercises, better be console-only ones. Do it until you understand everything reasonably well, including OOP with late binding, interfaces use and implementation and polymorphism (which is your issue related to your current question). After that come back. Honestly, one cannot explain it all in one Quick Answer, and without it you will be just wasting your time.

Best wishes in New Year!

—SA

Sergey Alexandrovich Kryukov 26-Dec-13 14:52pm

Now, CoreDispatcher is not an abstract class, but it has only the internal constructor(s), to allow construction from withing the framework only, to prevent direct creation of those instances. You should use the instance through the property Dispatcher of your Window instance.

Again, you mess up types and instances, which is a very basic issue.

—SA

AghaKhan 26-Dec-13 16:03pm

Thank you for your emails/reply.
Before I received your replies I started to look internal Constructor, but found out that
public sealed class CtrlCoreDispatcher : CoreDispatcher
{
}

Implementation inheritance is not allowed in WinRT. So I have to look something else to resolve this problem. I have to look something else beside inheritance.
Thanks for reply.

Best regards
Agha

Sergey Alexandrovich Kryukov 26-Dec-13 22:00pm

No! You don't need to look for something else. I told you exactly what to do, but you don't hear it. Take your window's Dispatcher property.

"Implementation inheritance is not allowed in WinRT" is gibberish. Inheritance cannot help here. The class is sealed, and also it cannot be directly installed. That's the general .NET and C# feature.

You are just not ready to do development. As simple as that. Learn the basics of programming and .NET, that's your "something else", the only thing that can possibly help you.

—SA

AghaKhan · Answer 2 · 2013-12-26T13:39:00

Solution 2

private CoreDispatcher _dispatcher = null;
public event PropertyChangedEventHandler PropertyChanged;

private async Task UIThreadAction(Action act)
{
await _dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => act.Invoke());
}
private async void PropertyChangedAsync(string property)
{
if (PropertyChanged != null)
await UIThreadAction(() => PropertyChanged(this, new PropertyChangedEventArgs(property)));
}

public FlipViewModel()
{
_dispatcher = Window.Current.Dispatcher;
}

Thanks Sergey Alexandrovich Kryukov

Posted 26-Dec-13 13:39pm

AghaKhan

Comments

Sergey Alexandrovich Kryukov 26-Dec-13 22:02pm

Have some shame! This is not "solution" but pure cheating. You cannot do engineering by kicking the TV set until it start showing picture. You have no idea how to write code. Please stop spamming this site. If you need help, we will gladly help you, but I already told you what you should do.
—SA

AghaKhan 26-Dec-13 22:55pm

Dear Brother:
Your comments are greatly appreciated. Someone should have to courage to say that. I have no problem with when you suggested “Have some shame”. Please guide me more. I love it. As you suggested "Implementation inheritance is not allowed in WinRT" is gibberish, but that is the error I received from my compiler and I am not making it up. I tried to implement solution but inheritance didn’t let me do so. I can send you the picture of my visual studio to show you that error if you wish. As you understand mistakes are the foundation of success and I do make mistakes. Please be my guide. Many times we write which is not following any design patterns but it works. Just Google “C# games by Agha Khan”. You will see about 4000 download.
Happy holidays

Best regards
Sergey Alexandrovich Kryukov
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Call from DLL (Window Runtime component)

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