CODEWITHSUNDEEP
androidmultithreadingandroid-activity
Andreas
Andreas

Reputation: 10037

How to tell if code needs to be run on the UI thread

I'm using a worker thread in my app so it's vital for me to know which code can be run from the worker thread and which code needs to be run on the UI thread.

In the Android documentation, the following hints can be found:

So, you must not manipulate your UI from a worker thread—you must do all manipulation to your user interface from the UI thread. [...] However, note that you cannot update the UI from any thread other than the UI thread or the "main" thread.

(source)

But what "manipulation to your user interface" means in practice is often not as clear as it seems. Of course, it's clear that you cannot hide views, manipulate button texts, add list view entries, etc. from a worker thread.

But what about calling setRequestedOrientation() from a worker thread, for example? Is that allowed or does it fall under UI manipulation and thus must be called from the UI thread? Is there any way to tell or should I stay safe and better run the code on the UI thread when in doubt?

Upvotes: 1

Views: 103

Answers (1)

D-Dᴙum
D-Dᴙum

Reputation: 7890

In general you should take guidance from the API documentation. For example the Activity.onCreate() explicitly states that:

This method must be called from the main thread of your app.

For the example you gave Activity.setRequestedOrientation() there is no explicit statement that the method should be called on a particular thread. Usually if threading is of concern the documentation will state that.

If you would prefer certainty then you called also call upon Activity.runOnUiThread()

Upvotes: 1

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