Android NumberPicker: Set min, max, default from XML

Here is an updated version that follows the Android Docs
(and thus supports theming & Android Studio designer preview)

values/attrs.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <declare-styleable name="NumberPickerWithXml">
        <attr name="maxValue" format="integer" />
        <attr name="minValue" format="integer" />
        <attr name="defaultValue" format="integer" />
    </declare-styleable>

</resources>

NumberPickerWithXml.kt:

package com.example.library.ui

import android.content.Context
import android.util.AttributeSet
import android.widget.NumberPicker
import com.example.library.ui.R

class NumberPickerWithXml : NumberPicker {

    constructor(context: Context) : super(context)

    constructor(context: Context, attrs: AttributeSet) : super(context, attrs) {
        processXmlAttributes(attrs)
    }

    constructor(context: Context, attrs: AttributeSet, defStyleAttr: Int) : super(context, attrs, defStyleAttr) {
        processXmlAttributes(attrs, defStyleAttr)
    }

    constructor(context: Context, attrs: AttributeSet, defStyleAttr: Int, defStyleRes: Int) : super(context, attrs, defStyleAttr, defStyleRes) {
        processXmlAttributes(attrs, defStyleAttr, defStyleRes)
    }

    private fun processXmlAttributes(attrs: AttributeSet, defStyleAttr: Int = 0, defStyleRes: Int = 0) {
        val attributes = context.theme.obtainStyledAttributes(attrs, R.styleable.NumberPickerWithXml, defStyleAttr, defStyleRes)

        try {
            this.minValue = attributes.getInt(R.styleable.NumberPickerWithXml_minValue, 0)
            this.maxValue = attributes.getInt(R.styleable.NumberPickerWithXml_maxValue, 0)
            this.value = attributes.getInt(R.styleable.NumberPickerWithXml_defaultValue, 0)
        } finally {
            attributes.recycle()
        }
    }

}

...or NumberPickerWithXml.java (untested):

package com.example.library.ui

import android.content.Context;
import android.util.AttributeSet;
import android.widget.NumberPicker;
import com.example.library.ui.R;

public class NumberPickerWithXml extends NumberPicker {

    public NumberPickerWithXml(Context context) {
        super(context);
    }

    public NumberPickerWithXml(Context context, AttributeSet attrs) {
        super(context, attrs);
        processXmlAttributes(attrs, 0, 0);
    }

    public NumberPickerWithXml(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        processXmlAttributes(attrs, defStyleAttr, 0);
    }

    public NumberPickerWithXml(Context context, AttributeSet attrs, int: defStyleAttr, int: defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        processXmlAttributes(attrs, defStyleAttr, defStyleRes);
    }

    private void processXmlAttributes(AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        TypedArray attributes = getContext().getTheme().obtainStyledAttributes(attrs, R.styleable.NumberPickerWithXml, defStyleAttr, defStyleRes);

        try {
            this.setMinValue(attributes.getInt(R.styleable.NumberPickerWithXml_minValue, 0));
            this.setMaxValue(attributes.getInt(R.styleable.NumberPickerWithXml_maxValue, 0));
            this.setValue(attributes.getInt(R.styleable.NumberPickerWithXml_defaultValue, 0));
        } finally {
            attributes.recycle();
        }
    }

}

Usage in your layout:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:custom="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <com.example.library.ui.NumberPickerWithXml
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        custom:defaultValue="30"
        custom:maxValue="120"
        custom:minValue="0" />

</LinearLayout>

You can try this:

<NumberPicker
  android:id="@+id/number_picker"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  app:minValue="@{0}"
  app:maxValue="@{120}"
  app:value="@{30}"/>

This works as part of Android Databinding. So, you might want to set it to true in your app level build.gradle.

android {
    ...

    dataBinding {
        enabled true
    }
}

I had the same problem, this is how I solved it (according to the comment of MKJParekh):

1. I created my own NumberPicker-Class

   package com.exaple.project;
   
   import android.annotation.TargetApi;
   import android.content.Context;
   import android.os.Build;
   import android.util.AttributeSet;
   import android.widget.NumberPicker;
   
   @TargetApi(Build.VERSION_CODES.HONEYCOMB)//For backward-compability
   public class MyNumberPicker extends NumberPicker {
   
       public MyNumberPicker(Context context) {
           super(context);
       }
   
       public MyNumberPicker(Context context, AttributeSet attrs) {
           super(context, attrs);
           processAttributeSet(attrs);
       }
   
       public MyNumberPicker(Context context, AttributeSet attrs, int defStyle) {
           super(context, attrs, defStyle);
           processAttributeSet(attrs);
       }
       private void processAttributeSet(AttributeSet attrs) {
           //This method reads the parameters given in the xml file and sets the properties according to it
           this.setMinValue(attrs.getAttributeIntValue(null, "min", 0));
           this.setMaxValue(attrs.getAttributeIntValue(null, "max", 0));
       }
   }
   

2. Now you can use this NumberPicker in your xml layout file

   <com.exaple.project.myNumberPicker
       android:id="@+id/numberPicker1"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:layout_gravity="center"
       android:orientation="vertical"
       max="100"
       min="1" />
   

Thanks to MKJParekh for his useful comment