How do I detect screen rotation

I have an activity that is showing a compass, and I need to know the orientation of the screen to properly rotate the needle. I need to distinguish between 90° and 270° degree rotation to properly handle this.

When I rotate the screen (on my Nexus S at least) the activity's onCreate gets called, e.g. when I rotate fro开发者_Python百科m portrait to landscape mode. When I rotate from one landscape mode to the other with the top edge raised, onCreate() gets called twice (once for portrait orientation and once for the target landscape mode).

However, when I rotate with the bottom edge up, the screen rotates 180° and onCreate is not getting called. Is there an event that gets fired in this case?

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You are correct that at a 180 degree rotation you will not get restarted or get a configuration change, because the configuration has not actually changed. (It is still in landscape or portrait, and everything else is the same.)

However if you are showing a compass, that must mean you are updating it from sensor events. Thus you can just call Display.getRotation() each time you get a sensor update to get the current rotation of the screen. In fact that you need is rotation of interpreting sensor events (or actually how your drawing of them will be modified when it gets to the screen), not just the orientation.

I found a relevant blog post that is well worth reading.

Be sure to read the SDK documentation.

Also check out the discussion about using Display.getRotation() to correctly remap sensor coordinates.

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The helper class OrientationEventListener makes it very easy to get call backs on rotation. I would suggest you give it a try.

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Just take a look at the SensorManager Documentation, there you can get the best examples and explanations of how to use the accelerometer to get the most precise informations. Instead of making the things just by detecting the phone orientation, with that API you can get the exactly rotation, just like used by racing games like Asphalt and Need For Speed.

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As Monchote said, in order to make your needle rotate as expected on the compass, it's better to lock your UI to portrait or landscape, and change your needle angle according to the device rotation angle, which can be gained easily from OrientationListener.

In this way, no matter the auto rotation feature is opened or not by user, you can always get rotation angle change notification. Here's a good example for your reference.

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Have a look at the OnConfigurationChanged method to track down the orientation change and re-arrange your UI as needed.

See some sample code