如何在C＃中使用反射获取列表类型元素

Question

I have a class : Transaction.cs

public class Transaction
{
    public int Transaction_id  { get; set; }
    public string Description { get; set; }
    public string Item { get; set; }
}

I want too use reflection to get the values that are in the collection of transactions ie :

var db = new List<Transaction>();
var temp = new Transaction { Transaction_id = 123, Item = "AKP", Description = "Startup" };
var info = temp.GetType().GetProperties();
db.Add(new Transaction { Transaction_id = 45, Item = "RW", Description = "Starting" });
var type = typeof(Transaction);
var prop = type.GetProperty("Item");
var value = prop.GetValue(temp);

added this code for loop on properties:

foreach (var testing in db.GetType().GetProperties())
{
    var sample = testing.GetValue(db);
    Console.WriteLine(sample);
}

i get a value of 4 displayed in command line.

which would give me the value of AKP on screen. Now how does it work when i have a list of transactions?

Thanks

Answer 1

For example if I want to set all of the properties to string.Empty in my class I would do something like this, you could apply the same logic in the foreach loop to get your property types etc..

public static void ConvertNullToStringEmpty<T>(this T clsObject) where T : class
{
    PropertyInfo[] properties = clsObject.GetType().GetProperties();//typeof(T).GetProperties();
    foreach (var info in properties)
    {
        // if a string and null, set to String.Empty
        if (info.PropertyType == typeof(string) && info.GetValue(clsObject, null) == null)
        {
            info.SetValue(clsObject, String.Empty, null);
        }
    }
}

Answer 2

Considering you got this list:

var transactionList = new List<Transaction>
{
   new Transaction { Transaction_id = 123, Item = "AKP", Description = "Startup" },
   new Transaction { Transaction_id = 45, Item = "RW", Description = "Starting" }
};

You can navigate property names of the each item in the collection by reading a single item's properties while iterating the list:

foreach (var item in transactionList)
{
     foreach (var property in item.GetType().GetProperties())
     {
         Console.WriteLine("{0}={1}", property.Name, property.GetValue(item, null));
     }                
}

Console.ReadLine();

Answer 3

Generic lists are type-safe so you don't need to use reflection.

To iterate over the list, use foreach .

var db = new List<Transaction>
{
    new Transaction { Transaction_id = 123, Item = "AKP", Description = "Startup" }, 
    new Transaction { Transaction_id = 45, Item = "RW", Description = "Starting" }
}
foreach (var transaction in db)
{
    Console.WriteLine(transaction.Item);
}

Output:

AKP
RW

If you truly need to use Reflection, and this sort of thing is common in your code base, I'd take the time to write an extension method like this one:

static T GetPropertyByName<T>(this object input, string name) 
{
    return (T)input
        .GetType()
        .GetProperty(name, BindingFlags.Instance)
        .GetValue(input);
}

And use it like this:

foreach (var transaction in db)
{
    Console.WriteLine(transaction.GetPropertyByName<string>("Item"));
}

Or if you don't know the names of the properties ahead of time:

foreach (var row in db)
{
    foreach (var p in row.GetType().GetProperties(BindingFlags.Instance))
    {
        Console.WriteLine(p.GetValue(row));
    }
}