How to check if running on UI thread in Android?

Question

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

how is this question a duplicate? – lasec0203 Sep 09 '21 at 05:10 — lasec0203, Sep 09 '21 at 05:10

score 125 · Answer 1 · edited Feb 19 '13 at 05:31

125

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()

edited Feb 19 '13 at 05:31

Malcolm

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answered Jul 17 '10 at 19:48

Dan Syrstad

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So just for the sake of explicitness, the actual check you can do is: (Looper.getMainLooper().getThread() == Thread.currentThread()) – greg7gkb Apr 23 '12 at 18:24
This anwer needs more love, thanks alot – Inverce Nov 20 '15 at 11:22
How do you run this in junit? – John Sardinha Jun 02 '20 at 12:48

score 85 · Answer 2 · edited Nov 19 '13 at 15:46

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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.

edited Nov 19 '13 at 15:46

Brais Gabin

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answered Jan 03 '12 at 14:49

balazsbalazs

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Short and sweet. Losing the `getThread()` is neat. – ahcox Mar 06 '12 at 19:10
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Worth noting although bbalazs mentions its from ICS, this is supported from API 1 onwards. So should be safe for all devices! – Chris.Jenkins May 20 '12 at 19:57
➕1 for reference to AOSP source. – CJBS Jan 13 '16 at 22:46
How do you run this in junit? – John Sardinha Jun 02 '20 at 12:48

score 12 · Accepted Answer · answered Dec 04 '09 at 09:34

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:

catch the android.view.ViewRoot$CalledFromWrongThreadException
post a Runnable to a view and check Thread.currentThread()
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.).

+1 for (3) < padding for the 15 limit > – Will Dec 04 '09 at 09:39 — Will, Dec 04 '09 at 09:39

score 2 · Answer 4 · answered Jan 31 '12 at 01:11

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If you want to know if you are in the main thread, you could maybe try:

Context c = **Get a Context**;
Thread.currentThread() == c.getMainLooper().getThread();

Of course, I could be wrong, and this could totally blow your app up.

answered Jan 31 '12 at 01:11

cesar

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A quick test suggests that this works well. – Kirill Rakhman May 18 '12 at 16:21
This works, but there's no need to get a context, see bbalazs's answer. – Kai Stavginski Jul 24 '13 at 09:24

How to check if running on UI thread in Android?

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