How to create a number picker dialog?

I have made a small demo of NumberPicker. This may not be perfect but you can use and modify the same.

public class MainActivity extends Activity implements NumberPicker.OnValueChangeListener
{
    private static TextView tv;
    static Dialog d ;
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tv = (TextView) findViewById(R.id.textView1);
        Button b = (Button) findViewById(R.id.button11);
         b.setOnClickListener(new OnClickListener()
         {

            @Override
            public void onClick(View v) {
                 show();
            }
            });
           }
     @Override
    public void onValueChange(NumberPicker picker, int oldVal, int newVal) {

         Log.i("value is",""+newVal);

     }

    public void show()
    {

         final Dialog d = new Dialog(MainActivity.this);
         d.setTitle("NumberPicker");
         d.setContentView(R.layout.dialog);
         Button b1 = (Button) d.findViewById(R.id.button1);
         Button b2 = (Button) d.findViewById(R.id.button2);
         final NumberPicker np = (NumberPicker) d.findViewById(R.id.numberPicker1);
         np.setMaxValue(100);
         np.setMinValue(0);
         np.setWrapSelectorWheel(false);
         np.setOnValueChangedListener(this);
         b1.setOnClickListener(new OnClickListener()
         {
          @Override
          public void onClick(View v) {
              tv.setText(String.valueOf(np.getValue()));
              d.dismiss();
           }    
          });
         b2.setOnClickListener(new OnClickListener()
         {
          @Override
          public void onClick(View v) {
              d.dismiss();
           }    
          });
       d.show();


    }
}

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

    <Button
        android:id="@+id/button11"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:text="Open" />

</RelativeLayout>

dialog.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <NumberPicker
        android:id="@+id/numberPicker1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="64dp" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/numberPicker1"
        android:layout_marginLeft="20dp"
        android:layout_marginTop="98dp"
        android:layout_toRightOf="@+id/numberPicker1"
        android:text="Cancel" />

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/button2"
        android:layout_alignBottom="@+id/button2"
        android:layout_marginRight="16dp"
        android:layout_toLeftOf="@+id/numberPicker1"
        android:text="Set" />

</RelativeLayout>

Edit:

under res/values/dimens.xml

<resources>

    <!-- Default screen margins, per the Android Design guidelines. -->
    <dimen name="activity_horizontal_margin">16dp</dimen>
    <dimen name="activity_vertical_margin">16dp</dimen>

</resources>

Consider using a Spinner instead of a Number Picker in a Dialog. It's not exactly what was asked for, but it's much easier to implement, more contextual UI design, and should fulfill most use cases. The equivalent code for a Spinner is:

Spinner picker = new Spinner(this);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_spinner_item, yourStringList);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
picker.setAdapter(adapter);

To show NumberPicker in AlertDialog use this code :

final AlertDialog.Builder d = new AlertDialog.Builder(context);
LayoutInflater inflater = this.getLayoutInflater();
View dialogView = inflater.inflate(R.layout.number_picker_dialog, null);
d.setTitle("Title");
d.setMessage("Message");
d.setView(dialogView);
final NumberPicker numberPicker = (NumberPicker) dialogView.findViewById(R.id.dialog_number_picker);
numberPicker.setMaxValue(50);
numberPicker.setMinValue(1);
numberPicker.setWrapSelectorWheel(false);
numberPicker.setOnValueChangedListener(new NumberPicker.OnValueChangeListener() {
    @Override
    public void onValueChange(NumberPicker numberPicker, int i, int i1) {
        Log.d(TAG, "onValueChange: ");
    }
});
d.setPositiveButton("Done", new DialogInterface.OnClickListener() {
    @Override
    public void onClick(DialogInterface dialogInterface, int i) {
        Log.d(TAG, "onClick: " + numberPicker.getValue());
    }
});
d.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
    @Override
    public void onClick(DialogInterface dialogInterface, int i) {
    }
});
AlertDialog alertDialog = d.create();
alertDialog.show();

number_picker_dialog.xml

<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_gravity="center"
android:gravity="center_horizontal">

<NumberPicker
    android:id="@+id/dialog_number_picker"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"/>
</LinearLayout>

For kotlin lovers.

fun numberPickerCustom() {
    val d = AlertDialog.Builder(context)
    val inflater = this.layoutInflater
    val dialogView = inflater.inflate(R.layout.number_picker_dialog, null)
    d.setTitle("Title")
    d.setMessage("Message")
    d.setView(dialogView)
    val numberPicker = dialogView.findViewById<NumberPicker>(R.id.dialog_number_picker)
    numberPicker.maxValue = 15
    numberPicker.minValue = 1
    numberPicker.wrapSelectorWheel = false
    numberPicker.setOnValueChangedListener { numberPicker, i, i1 -> println("onValueChange: ") }
    d.setPositiveButton("Done") { dialogInterface, i ->
        println("onClick: " + numberPicker.value)       
        }
    d.setNegativeButton("Cancel") { dialogInterface, i -> }
    val alertDialog = d.create()
    alertDialog.show()
}

and number_picker_dialog.xml

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_gravity="center"
    android:gravity="center_horizontal">

    <NumberPicker
        android:id="@+id/dialog_number_picker"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</LinearLayout>