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I am an Android Beginner. According to the lifecycle of an android application, when screen orientation is changed following methods are called:

onPause()
onStop()
onDestroy()
OnCreate()
onStart()
onResume()

But I have now added onConfigChanged in my XML file. When activity starts, onCreate, onStart and onResume are called. But when my screen orientation changes, only onConfigurationChanged method is called, the above mentioned methods are not called as shown below:

screenshot

Any reason for this?

Thanks in advance.

Şafak Gezer
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Gagan93
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2 Answers2

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Normally when an orientation , language , ... change happen the activity get destroyed and restarted and start the lifecycle from the begining unless you override the onConfigurationChanged function.

More details from Android documentation:

Configuration Changes

If the configuration of the device (as defined by the Resources.Configuration class) changes, then anything displaying a user interface will need to update to match that configuration. Because Activity is the primary mechanism for interacting with the user, it includes special support for handling configuration changes.

Unless you specify otherwise, a configuration change (such as a change in screen orientation, language, input devices, etc) will cause your current activity to be destroyed, going through the normal activity lifecycle process of onPause(), onStop(), and onDestroy() as appropriate. If the activity had been in the foreground or visible to the user, once onDestroy() is called in that instance then a new instance of the activity will be created, with whatever savedInstanceState the previous instance had generated from onSaveInstanceState(Bundle).

This is done because any application resource, including layout files, can change based on any configuration value. Thus the only safe way to handle a configuration change is to re-retrieve all resources, including layouts, drawables, and strings. Because activities must already know how to save their state and re-create themselves from that state, this is a convenient way to have an activity restart itself with a new configuration.

In some special cases, you may want to bypass restarting of your activity based on one or more types of configuration changes. This is done with the android:configChanges attribute in its manifest. For any types of configuration changes you say that you handle there, you will receive a call to your current activity's onConfigurationChanged(Configuration) method instead of being restarted. If a configuration change involves any that you do not handle, however, the activity will still be restarted and onConfigurationChanged(Configuration) will not be called.

youssefhassan
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It's a very good thing that only onConfigurationChanged() is called with orientation changes. It's actually preferred because it means that your initializations in onCreate() DON'T have to happen again -- you can reuse them with the new views that you rebind in onConfigurationChanged(). This results in a faster application that uses less memory and is less clunky.

Case in point:

You have a ListView. That ListView uses an ArrayAdapter. In onCreate(), you find the listView using findViewById(R.id.xxx) and you CREATE a NEW ArrayAdapter and set it for that listView. If every time onCreate() is called when the orientation changes, you would be creatting a new ArrayAdapter each and every time the orientation changes. Imagine switching the orientation 3 times -- what a waste!

Like this, you can create the ArrayAdapter in onCreate(), once, ever (when your application is created). And when the orientation changes, in onConfigurationChanged(), simply reset the ArrayAdapter for the new ListView you pick up again using findViewById(R.id.xxxx). Done. Only 1 ArrayAdapter has ever been created and it's data remains in tact for the new orientation.

Beautiful! :)

CompEng88
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