Welcome to the Lounge

class Program
{<br />
    static List<Person> people = new List<Person>();
    static void Main(string[] args)
    {
        people.Add(new Person { Name = "Joan", Age = 102 });
        people.Add(new Person { Name = "Pete", Age = 50 });
        people.Add(new Person { Name = "Walter", Age = 65 });
        people.Add(new Person { Name = "Joan", Age = 17 });
        people.Add(new Person { Name = "Walter", Age = 25 });

        var person1 = people.FindExact<Person>("Name", "Pete");
        var person2 = people.FindFirstExact<Person>("Name", "Walter");
        var person3 = people.FindLastExact<Person>("Name", "Joan");
    }
}
public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }

    public override string ToString()
    {
        return Name + " - " + Age.ToString();
    }
}

public static List<T> FindExact<T,P>(this List<T> list, string valuePropertyName, P propertyValue)
{
    List<T> found = default(List<T>);
    try
    {
        PropertyInfo info = typeof(T).GetProperty(valuePropertyName);
        found = (from item in list
                    let value = (string)(info.GetValue(item, null))
                    where (P)value == propertyValue
                    select item).ToList();
    }
    catch (Exception)
    {
    }
    return found;
}

void Main()
{
	 List<Person> people = new List<Person>();
        people.Add(new Person { Name = "Joan", Age = 102 });
        people.Add(new Person { Name = "Pete", Age = 50 });
        people.Add(new Person { Name = "Walter", Age = 65 });
        people.Add(new Person { Name = "Joan", Age = 17 });
        people.Add(new Person { Name = "Walter", Age = 25 });
 
        var person1 = people.FindExact<Person>("Name", "Pete");
        var person2 = people.FindFirstExact<Person>("Name", "Walter");
        var person3 = people.FindLastExact<Person>("Name", "Joan");
		
		person1.Dump();
		person2.Dump();
		person3.Dump();
}

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
 
    public override string ToString()
    {
        return Name + " - " + Age.ToString();
    }
}


public static class Extensions
{
	public static IEnumerable<T> FindExact<T>(this IEnumerable<T> list, string valuePropertyName, string text)
	{
		IEnumerable<T> found = default(IEnumerable<T>);
		try
		{
			PropertyInfo info = typeof(T).GetProperty(valuePropertyName);
			found = from item in list 
						let value = (string)(info.GetValue(item, null)) 
						where value == text 
						select item;
		}
		catch (Exception)
		{
		}
		return found;
	}
	
	public static T FindFirstExact<T>(this IEnumerable<T> list, string valuePropertyName, string text)
	{
		T found = default(T);
		try
		{
			found = list.FindExact(valuePropertyName, text).FirstOrDefault();
		}
		catch (Exception)
		{
		}
		return found;
	}
	
	public static T FindLastExact<T>(this IEnumerable<T> list, string valuePropertyName, string text)
	{
		T found = default(T);
		try
		{
			// Using Reverse here to not loop through the whole collection. 
			// Could add a check if here if IList is implemented and only use LastOrDefault() in that case
			found = list.Reverse().FindExact(valuePropertyName, text).First();
		}
		catch (Exception)
		{
		}
		return found;
	}
}

public static IEnumerable<T> FindExact<T>(this IEnumerable<T> list, string valuePropertyName, string text)
{
    IEnumerable<T> found = Enumerable.Empty<T>();

    try
    {
        PropertyInfo info = typeof(T).GetProperty(valuePropertyName);
        if (info != null && info.CanRead && info.PropertyType == typeof(string) && info.GetIndexParameters().Length == 0)
        {
            found = list.Where(item => item != null && (string)info.GetValue(item, null) == text).ToList();
        }
    }
    catch (Exception)
    {
    }
    
    return found;
}

Richard Deeming wrote:

You can eliminate most of the exceptions be checking that the property is found, can be read, returns a string, and doesn't have any index parameters; and by checking that the item is not null.

Richard Deeming wrote:

Throwing and catching an exception will seriously degrade your code's performance.

string name = (person != null) ? person.Name : string.Empty;

string name = person?.Name ?? string.Empty;

string name = string.Empty;
try
{
    name = person.Name;
}
catch (NullReferenceException)
{
}

Richard Deeming wrote:

found = list.Where(item => item != null && (string)info.GetValue(item, null) == text).ToList();

John Simmons / outlaw programmer wrote:

It is, after all, a list of <T>, so no item in the list will/should be null

var listOfStrings = new List<string>();
listOfStrings.Add(null);
listOfStrings.Add(default(string));