Added NumericUpDown class.

src/Avalonia.Controls/NumericUpDown/NumericUpDown.cs

@@ -0,0 +1,132 @@
+using System;
+using System.Globalization;
+
+namespace Avalonia.Controls
+{
+    /// <summary>
+    /// Base class for controls that represents a TextBox with button spinners that allow incrementing and decrementing numeric values.
+    /// </summary>
+    public abstract class NumericUpDown<T> : UpDownBase<T>
+    {
+        /// <summary>
+        /// Defines the <see cref="FormatString"/> property.
+        /// </summary>
+        public static readonly StyledProperty<string> FormatStringProperty =
+            AvaloniaProperty.Register<NumericUpDown<T>, string>(nameof(FormatString), string.Empty);
+
+        /// <summary>
+        /// Defines the <see cref="Increment"/> property.
+        /// </summary>
+        public static readonly StyledProperty<T> IncrementProperty =
+            AvaloniaProperty.Register<NumericUpDown<T>, T>(nameof(Increment), default(T), validate: OnCoerceIncrement);
+
+        /// <summary>
+        /// Initializes static members of the <see cref="NumericUpDown{T}"/> class.
+        /// </summary>
+        static NumericUpDown()
+        {
+            FormatStringProperty.Changed.Subscribe(FormatStringChanged);
+            IncrementProperty.Changed.Subscribe(IncrementChanged);
+        }
+
+        /// <summary>
+        /// Gets or sets the display format of the <see cref="UpDownBase{T}.Value"/>.
+        /// </summary>
+        public string FormatString
+        {
+            get { return GetValue(FormatStringProperty); }
+            set { SetValue(FormatStringProperty, value); }
+        }
+
+        /// <summary>
+        /// Gets or sets the amount in which to increment the <see cref="UpDownBase{T}.Value"/>.
+        /// </summary>
+        public T Increment
+        {
+            get { return GetValue(IncrementProperty); }
+            set { SetValue(IncrementProperty, value); }
+        }
+
+        /// <summary>
+        /// Called when the <see cref="FormatString"/> property value changed.
+        /// </summary>
+        /// <param name="oldValue">The old value.</param>
+        /// <param name="newValue">The new value.</param>
+        protected virtual void OnFormatStringChanged(string oldValue, string newValue)
+        {
+            if (IsInitialized)
+            {
+                SyncTextAndValueProperties(false, null);
+            }
+        }
+
+        /// <summary>
+        /// Called when the <see cref="Increment"/> property value changed.
+        /// </summary>
+        /// <param name="oldValue">The old value.</param>
+        /// <param name="newValue">The new value.</param>
+        protected virtual void OnIncrementChanged(T oldValue, T newValue)
+        {
+            if (IsInitialized)
+            {
+                SetValidSpinDirection();
+            }
+        }
+
+        /// <summary>
+        /// Called when the <see cref="Increment"/> property has to be coerced.
+        /// </summary>
+        /// <param name="baseValue">The value.</param>
+        protected virtual T OnCoerceIncrement(T baseValue)
+        {
+            return baseValue;
+        }
+
+        /// <summary>
+        /// Called when the <see cref="Increment"/> property value changed.
+        /// </summary>
+        /// <param name="e">The event args.</param>
+        private static void IncrementChanged(AvaloniaPropertyChangedEventArgs e)
+        {
+            if (e.Sender is NumericUpDown<T> upDown)
+            {
+                var oldValue = (T)e.OldValue;
+                var newValue = (T)e.NewValue;
+                upDown.OnIncrementChanged(oldValue, newValue);
+            }
+        }
+
+        /// <summary>
+        /// Called when the <see cref="FormatString"/> property value changed.
+        /// </summary>
+        /// <param name="e">The event args.</param>
+        private static void FormatStringChanged(AvaloniaPropertyChangedEventArgs e)
+        {
+            if (e.Sender is NumericUpDown<T> upDown)
+            {
+                var oldValue = (string) e.OldValue;
+                var newValue = (string) e.NewValue;
+                upDown.OnFormatStringChanged(oldValue, newValue);
+            }
+        }
+
+        private static T OnCoerceIncrement(NumericUpDown<T> numericUpDown, T value)
+        {
+            return numericUpDown.OnCoerceIncrement(value);
+        }
+
+        /// <summary>
+        /// Parse percent format text
+        /// </summary>
+        /// <param name="text">Text to parse.</param>
+        /// <param name="cultureInfo">The culture info.</param>
+        protected static decimal ParsePercent(string text, IFormatProvider cultureInfo)
+        {
+            var info = NumberFormatInfo.GetInstance(cultureInfo);
+            text = text.Replace(info.PercentSymbol, null);
+            var result = decimal.Parse(text, NumberStyles.Any, info);
+            result = result / 100;
+            return result;
+        }
+    }
+}