what does this code mean ?

Sanju Singh

hello ,
i am new to c# . i want to know what is happening in this code below. I am working in visual studio platform.
this.Dispatcher.BeginInvoke(DispatcherPriority.Background, (Action)(() => this.ProcessDepthData()));

thank you

4 Replies

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Vulpes11y ago
If you were to try and update controls from the background thread, the chances are that you would get a cross-thread exception:

"The calling thread cannot access this object because a different thread owns it."

or similar wording.

So it's definitely something you need to address if you are updating displayed images and the Dispatcher code you posted could, of course, be adapted to do that.

However, as the updating can only take place on the UI thread, you're not going to be able to update three images concurrently even if the images are created on separate background threads. You'll only be able to update them consecutively though if they display very quickly this shouldn't be a problem.

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Sanju Singh11y ago
thanks a lot Valpes. your comment is of great value.

well, how is this code different from creating a background thread and asking it to execute the desired method ? what i want to achieve is to update three bitmap images on my display window; in parallel .
yes i am capturing data from kinect sensors.If you have anything to through more light on this , please share.it will be of great help to me. thanks
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Vulpes11y ago
In WPF, you should only update controls from the thread on which they are created (normally the 'user interface' thread).

So code on a different thread needs to marshal such update operations back to the UI thread which is done by calling the Invoke or BeginInvoke method of the Dispatcher object for that thread.

As dinesh said, the Dispatcher object maintains a prioritized queue of operations for a particular thread.

The Invoke method is for synchronous operations and BeingInvoke for asynchronous operations and these methods (or, at any rate, the overload which is being used) cause the operation given by their second parameter to be added to the Dispatcher queue with the priority given by their first parameter.

In this case, the priority is 'Background' which means that operations are processed after all other non-idle operations are completed.

The operation itself is represented by a delegate and, nowadays, a lamda expression, converted to an Action delegate, is often passed for this parameter.

Here the operation is to call the ProcessDepthData() method which I assume is updating controls. In fact it sounds like it might be something to do with Kinect programming about which I know very little.

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dinesh kumar11y ago
Hi Sanju,

The Dispatcher maintains a prioritized queue of work items for a specific thread.
When a Dispatcher is created on a thread, it becomes the only Dispatcher that can be associated with the thread, even if the Dispatcher is shut down.
Executes the specified delegate asynchronously at the specified priority on the thread the Dispatcher is associated with. in this case the priority is in Background level so the methods which is called inside the Action() => delegate will be executed and there are many DispatcherPriority available in MSDN which would help you understand more in detail.

hope it helps.
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