How does the Dispatcher thread work in wpf a UI control

Question

How does the Dispatcher thread work in wpf a UI control?

Answer 1

Edit.

If you have a long running task, delegate it to a background thread using a BackGroundWorker, and then you won't need to use the dispatcher to pass messages back to the UI. This is a very good article.

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Its a very broad question. I suggest you start here with WPF Architecture.

Most objects in WPF derive from DispatcherObject, which provides the basic constructs for dealing with concurrency and threading. WPF is based on a messaging system implemented by the dispatcher. This works much like the familiar Win32 message pump; in fact, the WPF dispatcher uses User32 messages for performing cross thread calls.

There are really two core concepts to understand when discussing concurrency in WPF – the dispatcher and thread affinity.

During the design phase of WPF, the goal was to move to a single thread of execution, but a non-thread "affinitized" model. Thread affinity happens when a component uses the identity of the executing thread to store some type of state. The most common form of this is to use the thread local store (TLS) to store state. Thread affinity requires that each logical thread of execution be owned by only one physical thread in the operating system, which can become memory intensive. In the end, WPF’s threading model was kept in sync with the existing User32 threading model of single threaded execution with thread affinity. The primary reason for this was interoperability – systems like OLE 2.0, the clipboard, and Internet Explorer all require single thread affinity (STA) execution.

Given that you have objects with STA threading, you need a way to communicate between threads, and validate that you are on the correct thread. Herein lies the role of the dispatcher. The dispatcher is a basic message dispatching system, with multiple prioritized queues. Examples of messages include raw input notifications (mouse moved), framework functions (layout), or user commands (execute this method). By deriving from DispatcherObject, you create a CLR object that has STA behavior, and will be given a pointer to a dispatcher at creation time.