JAVASCRIPT

react-native-dropdown-picker

#go to the wesite and read the docs
Web_link: https://hossein-zare.github.io/react-native-dropdown-picker-website/docs/
    
#sample: 
#installation
npm install react-native-dropdown-picker

const [facultyOpen, setFacultyOpen] = useState(false);
const [facultyValue, setFacultyValue] = useState('electrical');
const [faculty, setFaculty] = useState([
    { label: 'Electrical & Computer Engineering', value: 'electrical' },
    { label: 'Civil Engineering', value: 'civil' },
    { label: 'Mechanical Engineering', value: 'mechanical' },
]);
#after-return
#used tailwind for style. delete all tw`` part if you don't use tailwind css
<View style={[tw`mb-3 z-50`]}>
          <Text
            style={[
              tw`font-semibold text-purple-600 ml-1 mb-1`,
              { fontSize: 18 },
            ]}
          >
            Faculty
          </Text>
          <DropDownPicker
            open={facultyOpen}
            value={facultyValue}
            items={faculty}
            setValue={setFacultyValue}
            setItems={setFaculty}
            setOpen={setFacultyOpen}
            style={[tw`bg-gray-200 w-full px-4 py-3 border-0`]}
            containerStyle={[tw`border-0 bg-gray-200 rounded-lg`]}
            dropDownContainerStyle={[
              tw``,
              {
                backgroundColor: '#E5E7EB',
                borderRadius: 10,
                zIndex: 1,
                borderWidth: 0,
              },
            ]}
          />
        </View>

style dropdown react native picker

<resources>
    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
     <item name="android:spinnerItemStyle">@style/SpinnerItem</item>
     <item name="android:spinnerDropDownItemStyle">@style/SpinnerDropDownItem</item>
    </style>

    <!-- Item selected font. -->
    <style name="SpinnerItem" parent="Theme.AppCompat.Light.NoActionBar">
     <item name="android:fontFamily">casual</item>
    </style>

    <!-- Dropdown options font. -->
    <style name="SpinnerDropDownItem" parent="Theme.AppCompat.Light.NoActionBar">
      <item name="android:fontFamily">casual</item>
      <item name="android:padding">8dp</item>
    </style>
<resources>