How to check if running on UI thread in Android? [duplicate]

Question

How can I know if the running code is executed on the main thread (UI thread)?
With Swing I use the isEventDispatchThread method...

Answer 1

Use Looper.getMainLooper().getThread() to get the UI thread. You can check if it is the current thread using the following expression:

Looper.getMainLooper().getThread() == Thread.currentThread()

Answer 2

It is UI thread if:

Looper.myLooper() == Looper.getMainLooper()

Source AOSP source code: ManagedEGLContext.java#L100, SharedPreferencesImpl.java#L470, Instrumentation.java#L1650 and so on.

Answer 3

Doesn't look like there is a method for that in the SDK. The check is in the ViewRoot class and is done by comparing Thread.currentThread() to a class member which is assigned in the constructor but never exposed.

If you really need this check you have several options to implement it:

1. catch the android.view.ViewRoot$CalledFromWrongThreadException
2. post a Runnable to a view and check Thread.currentThread()
3. use a Handler to do the same

In general I think instead of checking whether you're on the correct thread, you should just make sure the code is always executed on the UI thread (using 2. or 3.).