You can set your Xcode Device Orientation

Set in your android manifest file:
android:screenOrientation="portrait"
Or You can set it using Dimensions
. Something like this:
Dimensions.addEventListener('change', ({ window: { width, height } }) => {
const orientation = width > height ? 'LANDSCAPE' : 'PORTRAIT';
}
Or you can use react-native-orientation
to lock the screen on portrait or landscape just as you need. I have a working example in my github: https://github.com/soutot/react-native-orientation-test
class App extends Component {
componentDidMount() {
Orientation.lockToLandscape();
}
render() {
return(
<View style={{ flex: 1, justifyContent: 'center', alignItems: 'center'}}>
<Text>This is my content</Text>
</View>
);
}
}
Hope it helps