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It is not entirely clear to me how many Dispatchers there are in an application and how they are related to, or referenced from Threads.
As I understand it, a WPF application has 2 threads (one for input, the other for UI) and 1 dispatcher (associated to the UI-Thread). What if I create another thread - let's call it "worker thread" - when I call Dispatcher.CurrentDispatcher on the worker thread, which dispatcher will i get?
Another case: Assume a console application with 2 threads - the main thread, and an input-thread. On the main thread, I first create the input-thread and then i call Application.Run()
Thread thread = new Thread(new ThreadStart(UserInputThreadFunction)); thread.Start(); Application.Run(); There will be one dispatcher, right? On the input-thread, does Dispatcher.CurrentDispatcher return the dispatcher of the main thread? Or what is the proper way of getting an instance to the main thread's dispatcher?
Could it be, that there are more than one dispatcher in a WPF application? Is there any case, it would make sense to create another dispatcher?
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A Dispatcher is responsible for managing the work for a thread. The UI thread is the thread that renders the UI. The UI thread queues work items inside an object called a Dispatcher. The Dispatcher selects work items on a priority basis and runs each one to completion.
A dispatcher is often used to invoke calls on another thread. An example would be if you have a background thread working, and you need to update the UI thread, you would need a dispatcher to do it.
As I understand it, a WPF application has 2 threads (one for input, the other for UI) and 1 dispatcher (associated to the UI-Thread).
WPF supports a single-threaded apartment model that has the following rules: One thread runs in the entire application and owns all the WPF objects. WPF elements have thread affinity, in other words other threads can't interact with each other.
WPF application has 2 threads (one for input, the other for UI)
This statement is not entirely correct. A WPF application has only one UI thread that handles all the UI interaction and user input. There is also a "hidden" thread responsible for rendering, but normally developers don't deal with it.
Dispatcher / Thread relationship is one to one, i.e. one Dispatcher is always assoticated with one thread and can be used to dispatch execution to that thread. Dispatcher.CurrentDispatcher returns the dispatcher for the current thread, that is, when you call Dispatcher.CurrentDispatcher on a worker thread you get a dispatcher for that working thread.
Dispatchers are created on demand, which means if you access Dispatcher.CurrentDispatcher and there is no dispatcher associated with the current thread, one will be created.
That being said, the number of dispatchers in the application is always less or equal to the number of threads in the application.
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