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C# Automatic Property Default Value Extension Methods

, 23 Aug 2011 CPOL
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For .NET 4.0:using System;using System.Collections.Generic;using System.ComponentModel;using System.Reflection;using System.Linq.Expressions;static class AutomaticPropertyExtensions{ private static class Cache where T : class { public static readonly...
For .NET 4.0:
 
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Reflection;
using System.Linq.Expressions;
 
static class AutomaticPropertyExtensions
{
    private static class Cache<T> where T : class
    {
        public static readonly Action<T> Init;
        public static readonly int PropertyCount;
 
        static Cache()
        {
            var p = Expression.Parameter(typeof(T), "this");
            var body = Expression.Block(typeof(T)
                .ListPropertiesToReset()
                .Select(pair => Assign(p, pair.Item1, pair.Item2)));
 
            PropertyCount = body.Expressions.Count;
            if (PropertyCount != 0)
            {
                var result = Expression.Lambda<Action<T>>(body, p);
                Init = result.Compile();
            }
        }
    }
    
    private static Expression Assign(Expression p, PropertyInfo property, object value)
    {
        var prop = Expression.Property(p, property);
        var defaultValue = Expression.Constant(value, property.PropertyType);
        return Expression.Assign(prop, defaultValue);
    }
    
    private static IEnumerable<Tuple<PropertyInfo, object>> ListPropertiesToReset(this Type componentType)
    {
        const BindingFlags flags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic;
 
        return from PropertyInfo property in componentType.GetProperties(flags)
               where property.CanWrite
               let attributes = property.GetCustomAttributes(typeof(DefaultValueAttribute), true)
               where attributes != null && 0 != attributes.Length
               let attribute = (DefaultValueAttribute)attributes[0]
               let defaultValue = attribute.Value
               where defaultValue != null
               select Tuple.Create(property, defaultValue);
    }
 
    public static int ResetPropsUsingDefaultAttributes<T>(this T instance) where T : class
    {
        if (instance == null) throw new ArgumentNullException("instance");
        if (Cache<T>.Init != null) Cache<T>.Init(instance);
        return Cache<T>.PropertyCount;
    }
}
 
Usage:
public class TestClass
{
    [DefaultValue(0.3141)]
    public double MyPie { get; set; }
 
    [DefaultValue("Pizza")]
    public string MyLove { get; set; }
 
    public TestClass()
    {
        this.Reset();
    }
 
    public void Reset()
    {
        this.ResetPropsUsingDefaultAttributes();
    }
 
    public override string ToString()
    {
        return string.Format("MyPie = {0}, MyLove = {1}",
            MyPie, MyLove == null ? "null" : MyLove);
    }
}

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Richard Deeming
Software Developer Nevalee Business Solutions
United Kingdom United Kingdom
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Comments and Discussions

 
GeneralReason for my vote of 5 Quite an improvement. Doesn't look a... PinmemberItai Basel23-Aug-11 12:29 

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