Android, how to not destroy the activity when I rotate the device?

Question

For API 12 and below: add

android:configChanges="orientation"

Add "screenSize" if you are targeting API 13 or above because whenever your orientation changes so does your screen size, otherwise new devices will continue to destroy your activity. See Egg's answer below for more information on using "screenSize"

android:configChanges="orientation|screenSize"

to your Activity in AndroidManifest.xml. This way your Activity wont be restarted automatically. See the documentation for more infos

From the official document flurin said,

Note: If your application targets API level 13 or higher (as declared by the minSdkVersion and targetSdkVersion attributes), then you should also declare the "screenSize" configuration, because it also changes when a device switches between portrait and landscape orientations.

So if your app targets API level 13 or higher, you should set this config instead:

android:configChanges="orientation|screenSize"

The right solution is

android:configChanges="orientation|screenSize"

Android documentation:

The current available screen size has changed. This represents a change in the currently available size, relative to the current aspect ratio, so will change when the user switches between landscape and portrait. However, if your application targets API level 12 or lower, then your activity always handles this configuration change itself (this configuration change does not restart your activity, even when running on an Android 3.2 or higher device).*

I was messing this up for a little bit and then relized that inside the Manifest file I was putting the configChanges on the Application level and not on the Activity Level. Here is what the code looks like when it is correctly working for me.

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
        <activity android:name=".MainActivity"
                  android:configChanges="orientation|screenSize|keyboardHidden">
        <intent-filter>
            <action android:name="android.intent.action.MAIN"/>
            <category android:name="android.intent.category.LAUNCHER"/>
        </intent-filter>
    </activity> 
</application> 

Now that Android supports split screen ("multi-window" in Android parlance), you'll probably want to add screenSize|smallestScreenSize|screenLayout|orientation as well. So to handle rotation and split screen you'll want something like this in android:configChanges

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
        <activity android:name=".MainActivity"
                  android:configChanges="orientation|screenSize|keyboardHidden|smallestScreenSize|screenLayout">
        <intent-filter>
            <action android:name="android.intent.action.MAIN"/>
            <category android:name="android.intent.category.LAUNCHER"/>
        </intent-filter>
    </activity> 
</application>