NumberWithUnitPicker

NumberWithUnitPickerCell.cs

using AiForms.Renderers;
using Xamarin.Forms;

namespace AiForms.Renderers
{
    public class NumberWithUnitPickerCell: NumberPickerCell
    {
        public static BindableProperty UnitProperty = BindableProperty.Create(nameof (Unit), typeof (string), typeof (NumberWithUnitPickerCell), "", BindingMode.TwoWay);
        
        public string Unit
        {
            get => (string) this.GetValue(UnitProperty);
            set => this.SetValue(UnitProperty, value);
        }
    }
}

NumberWithUnitPickerCellRenderer_Android.cs

using System;
using AiForms.Renderers;
using AiForms.Renderers.Droid;
using Android.Content;
using Android.Runtime;
using Android.Text;
using Android.Widget;
using Java.Lang;
using Java.Lang.Reflect;
using Xamarin.Forms;
using APicker = Android.Widget.NumberPicker;
using Exception = System.Exception;
using Object = Java.Lang.Object;
using String = System.String;

[assembly: ExportRenderer(typeof(NumberWithUnitPickerCell), typeof(NumberWithUnitPickerCellRenderer))]
namespace AiForms.Renderers.Droid
{
    [Android.Runtime.Preserve(AllMembers = true)]
    public class NumberWithUnitPickerCellRenderer : CellBaseRenderer<NumberWithUnitPickerCellView> { }

    /// <summary>
    /// Number picker cell view.
    /// </summary>
    [Android.Runtime.Preserve(AllMembers = true)]
    public class NumberWithUnitPickerCellView : NumberPickerCellView
    {
        public NumberWithUnitPickerCellView(Context context, Cell cell) 
            : base(context, cell)
        {
        }

        public NumberWithUnitPickerCellView(IntPtr javaReference, JniHandleOwnership transfer) 
            : base(javaReference, transfer)
        {
        }
        
        NumberWithUnitPickerCell _NumberPickerCell => Cell as NumberWithUnitPickerCell;
        
        protected override string FormatNumber(int? number)
        {
            return number.HasValue && !String.IsNullOrEmpty(_NumberPickerCell.Unit)
                ? $"{number} {_NumberPickerCell.Unit}"
                : number?.ToString() ?? "";
        }

        protected override void OnPickerCreated(NumberPicker picker)
        {
            base.OnPickerCreated(picker);

            if (!String.IsNullOrEmpty(_NumberPickerCell.Unit))
            {
                picker.SetFormatter(new UnitFormatter(_NumberPickerCell.Unit));
                ApplyInitialFormattingBugfix(picker);
            }
        }

        // see bug https://stackoverflow.com/questions/17708325/android-numberpicker-with-formatter-doesnt-format-on-first-rendering/54083214#54083214
        // and https://issuetracker.google.com/issues/36952035
        private void ApplyInitialFormattingBugfix(NumberPicker picker)
        {
            try
            {

                Class klass = Java.Lang.Class.FromType(typeof(NumberPicker));
                Field f = klass.GetDeclaredField("mInputText");
                f.Accessible = true;
                EditText inputText = (EditText) f.Get(picker);
                inputText.SetFilters(new IInputFilter[0]);
            }
            catch (Exception)
            {
                // silently ignore this
            }
        }
    }

    internal class UnitFormatter : Object, NumberPicker.IFormatter
    {
        private readonly string _unit;

        public UnitFormatter(string unit)
        {
            _unit = unit;
        }

        public string Format(int value)
        {
            return value + " " + _unit;
        }
    }
}

NumberWithUnitPickerCellRenderer_iOS.cs

using System;
using AiForms.Renderers;
using AiForms.Renderers.iOS;
using UIKit;
using Xamarin.Forms;
using XFSpike.iOS;

[assembly: ExportRenderer(typeof(NumberWithUnitPickerCell), typeof(NumberWithUnitPickerCellRenderer))]
namespace XFSpike.iOS
{
    [Foundation.Preserve(AllMembers = true)]
    public class NumberWithUnitPickerCellRenderer : CellBaseRenderer<NumberWithUnitPickerCellView> { }

    [Foundation.Preserve(AllMembers = true)]
    public class NumberWithUnitPickerCellView : NumberPickerCellView
    {
        public NumberWithUnitPickerCellView(Cell formsCell) : base(formsCell)
        {
        }

        NumberWithUnitPickerCell _NumberPickerCell => Cell as NumberWithUnitPickerCell;
        
        protected override string FormatNumber(int? number)
        {
            return number.HasValue && !String.IsNullOrEmpty(_NumberPickerCell.Unit)
                ? $"{number} {_NumberPickerCell.Unit}"
                : number?.ToString() ?? "";
        }

        protected override NumberPickerSource CreateNumberPickerSource()
        {
            return new NumberWithUnitPickerSource(_NumberPickerCell.Unit);
        }
    }

    [Foundation.Preserve(AllMembers = true)]
    internal class NumberWithUnitPickerSource : NumberPickerSource
    {
        private readonly string _unit;

        public NumberWithUnitPickerSource(string unit)
        {
            _unit = unit;
        }
        
        public override string GetTitle(UIPickerView picker, nint row, nint component)
        {
            int  number = Items[(int)row];
            return String.IsNullOrEmpty(_unit)
                ? number.ToString()
                : $"{number} {_unit}";
        }
    }
}