Comments on Eric De C#: Good practice to use Dispatcher in WPF background ...

---------------- VB.NET version ---------------- ...

2011-09-16T20:06:06.613-04:00

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VB.NET version
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Public Shared Sub Dispatch(Of TSource As DispatcherObject, T1, T2)(ByRef source As TSource, func As Action(Of TSource, T1, T2), param1 As T1, param2 As T2)
If source.Dispatcher.CheckAccess Then func(source, param1, param2)
source.Dispatcher.Invoke(func, source, param1, param2)
End Sub

Hello! I don't know how in wpf, but in Silverl...

2011-07-19T00:41:55.378-04:00

Hello!
I don't know how in wpf, but in Silverlight 4 the method Dispatcher.CheckAccess() is invisible for Intellisense,

because it has been marked with a [EditorBrowsable(EditorBrowsableState.Never)] attribute. Probably, Microsoft

doesn't want developers to use Dispatcher.CheckAccess(). Taking into account that all controls, including page, are

created inside the UI thread, inside a page constructor the property Thread.CurrentThread.ManagedThreadId is the

required UI thread identifier. We can use this fact it in the next way:
[csharp]
using System;
using Microsoft.Phone.Controls;

namespace WindowsPhoneApplication1
{
public partial class MainPage : PhoneApplicationPage
{
private int _uiThreadID = -1;

private bool IsUIThread
{
get { return _uiThreadID == System.Threading.Thread.CurrentThread.ManagedThreadId; }
}

// Constructor
public MainPage()
{
// preserve UI thread id
_uiThreadID = System.Threading.Thread.CurrentThread.ManagedThreadId;
InitializeComponent();
}

public void UpdateSomeTextBox(string text)
{
if (IsUIThread) // if it's UI thread, just set the new text directly
someTextBox.Text = text;
else // otherwise, invoke UpdateSomeTextBox in UI thread
Dispatcher.BeginInvoke(delegate()
{
UpdateSomeTextBox(text);
});
}
}
}
[/csharp]
I've described it in details in my post in blog here http://dotnetfollower.com/wordpress/2011/07/silverlight-for-windows-phone-7-how-to-check-if-

the-current-thread-is-ui-one/

Thank you!
.Net Follower (http://dotnetfollower.com)

You might also consider enhancing these methods wi...

2011-03-04T10:19:44.407-05:00

You might also consider enhancing these methods with a DispatcherPriority parameter that can be passed directly on to the Dispatcher.Invoke method.

Yes, it would help me especially when lambda funct...

2011-01-24T17:42:02.948-05:00

Yes, it would help me especially when lambda functions are involved. And as far as adding the Action/Func overloads, wouldn't you be able to completely replace all of your current overloads with Action and Func overloads while maintaining all functionality? Some samples of those would be greatly appreciated as well! Thanks.

If you really need sample for those overload, I ca...

2011-01-24T17:02:07.854-05:00

If you really need sample for those overload, I can publish some but I don't think its necessary to understand the concept.

Actually because this API is based on Action<> and Func<> API it would be a good idea to add all Action<> and Func<> overloads. This way you could use this API anywhere you would use Action<> or Func<> definition.

Great approach, Eric. Could you help out with my ...

2011-01-24T16:50:52.151-05:00

Great approach, Eric. Could you help out with my understanding of some of the overloads by posting some additional samples? Specifically, two samples of invoking with one parameter, one returning a result and the other not returning a result. Thanks!

Hi there Eric, Thanks for this bit of code. It si...

2010-12-10T02:06:13.925-05:00

Hi there Eric,

Thanks for this bit of code. It simplifies a number of our UI synchronization calls.

We did notice one small issue. If a Dispatch was underway when the main application was shutting down, a NullReferenceException was thrown on the following line:

return (TResult)source.Dispatcher.Invoke(func);

I noticed that at this point the source.Dispatcher.HasShutdownStarted property is true (under normal circumstances it was false).

To fix this we put in a check at the start of the Dispatch call which returns immediately (without calling the functor):

// For public TResult methods
if (source.Dispatcher.HasShutdownStarted || source.Dispatcher.HasShutdownFinished)
return default(TResult);

// for public void methods
if (source.Dispatcher.HasShutdownStarted || source.Dispatcher.HasShutdownFinished)
return;

Hope this helps in case anyone else stumbles over a similar issue.

Cheers

Rod

Excellent!!!

2010-09-14T18:04:09.781-04:00

Excellent!!!

Great post. You help me!

2010-05-21T11:55:03.588-04:00

Great post. You help me!

A fantastic post. I'm very much interested abo...

2010-03-16T09:10:25.686-04:00

A fantastic post. I'm very much interested about the testing part of code written in Dispatcher.