Android - can I increase the textSize for the NumberPicker widget?

I was facing the same problem, I wanted to increase the text size of the NumberPicker but couldn't find a way to do it as part of the Widget. All the above answers are great, but instead I went with the following solution, which met my needs:

<NumberPicker
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:scaleX="1.5"
    android:scaleY="1.5"/>

This essentially magnifies the entire Widget.

The following worked for me (in API 15 / 4.0.3)

note: aheuermann's solution is safe against potential implementation differences in the NumberPicker's layout across different Android versions (that is, the TextView may not always be at child position 1).

TextView tv1 = (TextView)_numberPicker.getChildAt(1);
tv1.TextSize = 10;

I was able to accomplish this by extending the default NumberPicker. Not ideal, but it works.

public class NumberPicker extends android.widget.NumberPicker {

   public NumberPicker(Context context, AttributeSet attrs) {
     super(context, attrs);
   }

   @Override
   public void addView(View child) {
     super.addView(child);
     updateView(child);
   }

   @Override
   public void addView(View child, int index, android.view.ViewGroup.LayoutParams params) {
     super.addView(child, index, params);
     updateView(child);
   }

   @Override
   public void addView(View child, android.view.ViewGroup.LayoutParams params) {
     super.addView(child, params);
     updateView(child);
   }

   private void updateView(View view) {
     if(view instanceof EditText){
       ((EditText) view).setTextSize(25);
       ((EditText) view).setTextColor(Color.parseColor("#333333"));
     }
   }

 }

Then just reference this class in your layout xml.

<com.yourpackage.NumberPicker
        android:id="@+id/number_picker"
        android:layout_width="43dp"
        android:layout_height="wrap_content" />

only set this sytle for your NumberPicker:

   <style name="AppTheme.Picker" parent="Theme.AppCompat.Light.NoActionBar" >
    <item name="android:textColorPrimary">@android:color/white</item>
    <item name="android:textSize">20dp</item>
</style>

<NumberPicker
        android:theme="@style/AppTheme.Picker"
        android:id="@+id/yearNumberPicker"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

and <item name="android:textColorPrimary">@android:color/white</item> change textcolor :