Can you access UI elements from another thread? (get not set)

Question

I see a lot of threads on google/here on UPDATING a UI element from another thread.

What if I want to just get the value of a checkbox?

Am I able to do this

Answer 1

Can you access UI elements from another thread? (get not set)?

No.

Here is the deal. UI elements have very strict thread affinity requirements. This means you can only access the element from the thread hosting it. This includes all kinds of accesses including simple reads.¹

It may work fine for simple property getters, but its perceived safeness would be an accidental result of the way that particular control was implemented. Since Control instances have thread affinity they could potentially use thread local storage techniques to save some of their state which, of course, would not be compatible with different thread. Or what if the value you are trying to read is in a half-baked state? There would be no way to synchronize access to that read since the write may be occurring inside code you have no control over. And still this is ignoring subtle memory barrier problems that may arise.

Again, if it appears to work then chalk it up as an accident. Accessing UI elements from a thread than the one hosting them is a recipe for disaster. Things may fail unpredictably and spectacularly.

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¹There are very few exceptions to this rule. Using the ISynchronizeInvoke methods is one such exception.