prs/prs.mobile/comal.timesheets/Data Models/Abstractions/Shell.cs

using System.Collections.Generic;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using InABox.Core;
using Xamarin.Forms;

namespace comal.timesheets
{
    public abstract class Shell<TParent,TEntity> : BindableObject, INotifyPropertyChanged, IShell
        where TParent : IModel
        where TEntity : Entity
    {
        
        #region INotifyPropertyChanged
        
        public event PropertyChangedEventHandler PropertyChanged;
        
        protected void DoPropertyChanged(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
        
        protected bool SetProperty<T>(ref T field, T value, [CallerMemberName] string propertyName = null)
        {
            if (EqualityComparer<T>.Default.Equals(field, value)) return false;
            field = value;
            DoPropertyChanged(propertyName);
            return true;
        }

        
        #endregion
        
        protected virtual void RowChanged()
        {
            
        }
        
        private CoreRow _row = null;
        public CoreRow Row
        {
            get => _row;
            set
            {
                _row = value;
                RowChanged();
            }
        }
        
        public TParent Parent { get; set; }

        IModel IShell.Parent => this.Parent;
        
        #region Row Get/Set Caching
        
        // We do this for three reasons:
        // 1. Rather than define properties in once class and columns in another,
        // we can define and link properties and columns in the one class,
        // using a _static_ constructor, which reduces complexity
        // 2. By caching based on the property name, we eliminate the need to convert
        // expressions to strings (expensive), while still retaining type-safety
        // 3. Using the Get/Set helper functions reduces code complexity when defining 
        // shell properties, and distinguishes between data and calculated properties
        
        private static ShellColumns<TParent,TEntity> _columns = new ShellColumns<TParent,TEntity>();
        public static ShellColumns<TParent,TEntity> Columns
        {
            get {  return _columns; }
        }

        protected virtual T Get<T>([CallerMemberName] string property = null)
        {
            var value = Row.Values[Columns.IndexOf(property)];
            return value != null ? (T)CoreUtils.ChangeType(value, typeof(T)) : CoreUtils.GetDefault<T>();        
        }
        
        protected virtual void Set<T>(T value, bool notify = true, [CallerMemberName] string property = null)
        {            
            Row.Values[Columns.IndexOf(property)] = value;
            if (notify)
                DoPropertyChanged(property);
        }

        #endregion
        
    }

}