how to change number picker style in android?

Preview of a customized number picker:

<NumberPicker
  android:id="@+id/np"
  android:layout_width="40dp"
  android:layout_height="40dp"
  android:layout_centerHorizontal="true"
  android:background="@drawable/drawablenp"
  android:layout_centerVertical="true"/>

Create the background xml in the drawable folder named "drawablenp.xml"

<?xml version="1.0" encoding="utf-8"?>
<shape
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">

    <gradient
        android:startColor="#707070"
        android:centerColor="#f8f8f8"
        android:endColor="#707070"
        android:angle="270"/>

</shape>

Make copy of library/res/drawable-*/numberpicker_selection_divider.9.png and name then, for example, custom_np_sd.9.png.

Override default NumberPicker style via activity theme:

<style name="AppTheme" parent="@style/Holo.Theme">
  <item name="numberPickerStyle">@style/CustomNPStyle</item>
</style>
<style name="CustomNPStyle" parent="@style/Holo.NumberPicker">
  <item name="selectionDivider">@drawable/custom_np_sd</item>
</style>

And apply @style/AppTheme as activity theme.

Unfortunately, you can't style it. The styles and styling attributes for NumberPicker are not present in the public API, therefore you can't set them and change the default look. You can only select between light and dark theme.

As a solution I would suggest to use android-numberpicker library instead. The library is basically a port of NumberPicker extracted from Android source codes. But it's better than that, it also backports NumberPicker to Android 2.x. The library can be easily styled.

To style the divider adjust NPWidget.Holo.NumberPicker style and its selectionDivider and selectionDividerHeight attributes.
To style the text adjust NPWidget.Holo.EditText.NumberPickerInputText style.

I faced this problem too. I really want to have nice NumberPicker UI. All answer in this question worked but very limited. I almost create my own RecylerView to create the NumberPicker I want. Apparently I found neat library which is very robust. Here is the link https://github.com/Carbs0126/NumberPickerView

Not trying to answer the question here. Just want to help someone with the same problem as I am.