MvvmCrossRaiseAndSetIfChanged.cs

using Cirrious.MvvmCross.ViewModels;
using System;
using System.Collections.Generic;
using System.Diagnostics.Contracts;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;

namespace Blah
{
    public static class MvvmCrossRaiseAndSetIfChanged
    {
        /// <summary>
        /// RaiseAndSetIfChanged fully implements a Setter for a read-write
        /// property on a ReactiveObject, using CallerMemberName to raise the notification
        /// and the ref to the backing field to set the property.
        /// 
        /// This method is copied from ReactiveUI/ReactiveObject.cs as it only works on ReactiveObject
        /// </summary>
        /// <typeparam name="TObj">The type of the This.</typeparam>
        /// <typeparam name="TRet">The type of the return value.</typeparam>
        /// <param name="This">The <see cref="ReactiveObject"/> raising the notification.</param>
        /// <param name="backingField">A Reference to the backing field for this
        /// property.</param>
        /// <param name="newValue">The new value.</param>
        /// <param name="propertyName">The name of the property, usually
        /// automatically provided through the CallerMemberName attribute.</param>
        /// <returns>The newly set value, normally discarded.</returns>
        public static TRet RaiseAndSetIfChanged<TObj, TRet>(
                this TObj This,
                ref TRet backingField,
                TRet newValue,
                [CallerMemberName] string propertyName = null)
            where TObj : MvxViewModel
        {
            Contract.Requires(This != null);
            Contract.Requires(propertyName != null);

            if (EqualityComparer<TRet>.Default.Equals(backingField, newValue))
            {
                return newValue;
            }

            backingField = newValue;
            This.RaisePropertyChanged(propertyName);
            return newValue;
        }
    }
}