Xamarin.Forms BindablePicker

forms-bindable-picker.cs

// via https://forums.xamarin.com/discussion/19079/data-binding-for-the-items-source-of-a-picker-control

using System;
using System.Collections;
using Xamarin.Forms;

public class BindablePicker : Picker {
    public BindablePicker() {
        this.SelectedIndexChanged += OnSelectedIndexChanged;
    }

    public static BindableProperty ItemsSourceProperty =
        BindableProperty.Create<BindablePicker, IEnumerable>(o => o.ItemsSource, default(IEnumerable), propertyChanged: OnItemsSourceChanged);

    public static BindableProperty SelectedItemProperty =
        BindableProperty.Create<BindablePicker, object>(o => o.SelectedItem, default(object), propertyChanged: OnSelectedItemChanged);


    public IEnumerable ItemsSource {
        get { return (IEnumerable)GetValue(ItemsSourceProperty); }
        set { SetValue(ItemsSourceProperty, value); }
    }

    public object SelectedItem {
        get { return (object)GetValue(SelectedItemProperty); }
        set { SetValue(SelectedItemProperty, value); }
    }

    private static void OnItemsSourceChanged(BindableObject bindable, IEnumerable oldvalue, IEnumerable newvalue) {
        var picker = bindable as BindablePicker;
        picker.Items.Clear();
        if (newvalue != null) {
            //now it works like "subscribe once" but you can improve
            foreach (var item in newvalue) {
                picker.Items.Add(item.ToString());
            }
        }
    }

    private void OnSelectedIndexChanged(object sender, EventArgs eventArgs) {
        if (SelectedIndex < 0 || SelectedIndex > Items.Count - 1) {
            SelectedItem = null;
        } else {
            SelectedItem = Items[SelectedIndex];
        }
    }
    private static void OnSelectedItemChanged(BindableObject bindable, object oldvalue, object newvalue) {
        var picker = bindable as BindablePicker;
        if (newvalue != null) {
            picker.SelectedIndex = picker.Items.IndexOf(newvalue.ToString());
        }
    }
}