java.lang.IllegalStateException: Only fullscreen opaque activities can request orientation

In android Oreo (API 26) you can not change orientation for Activity that have below line(s) in style

 <item name="android:windowIsTranslucent">true</item>

or

 <item name="android:windowIsFloating">true</item>

You have several way to solving this :

1) You can simply remove above line(s) (or turn it to false) and your app works fine.

2) Or you can first remove below line from manifest for that activity

android:screenOrientation="portrait"

Then you must add this line to your activity (in onCreate())

    //android O fix bug orientation
    if (android.os.Build.VERSION.SDK_INT != Build.VERSION_CODES.O) {
        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
    }

3) You can create new styles.xml in values-v26 folder and add this to your style.xml. (Thanks to AbdelHady comment)

 <item name="android:windowIsTranslucent">false</item>
 <item name="android:windowIsFloating">false</item>

In Android O and later this error happens when you set

 android:screenOrientation="portrait"

in Manifest.

Remove that line and use

 setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

in your activity.

This will fix your issue.

Google throws this exception on Activity's onCreate method after v27, their meaning is : if an Activity is translucent or floating, its orientation should be relied on parent(background) Activity, can't make decision on itself.

Even if you remove android:screenOrientation="portrait" from the floating or translucent Activity but fix orientation on its parent(background) Activity, it is still fixed by the parent, I have tested already.

One special situation : if you make translucent on a launcher Activity, it has't parent(background), so always rotate with device. Want to fix it, you have to take another way to replace <item name="android:windowIsTranslucent">true</item> style.