CODEWITHSUNDEEP
c#custom-attributes
Rush Frisby
Rush Frisby

Reputation: 11464

Retrieve custom attribute parameter values?

if i have created an attribute:

public class TableAttribute : Attribute {
    public string HeaderText { get; set; }
}

which i apply to a few of my properties in a class

public class Person {
    [Table(HeaderText="F. Name")]
    public string FirstName { get; set; }
}

in my view i have a list of people which i am displaying in a table.. how can i retrieve the value of HeaderText to use as my column headers? Something like...

<th><%:HeaderText%></th>

Upvotes: 14

Views: 22093

Answers (2)

ScubaSteve
ScubaSteve

Reputation: 8270

Jon Skeet's solution is good if you allow multiple attributes of the same type to be declared on a property. (AllowMultiple = true)

ex:

[Table(HeaderText="F. Name 1")]
[Table(HeaderText="F. Name 2")]
[Table(HeaderText="F. Name 3")]
public string FirstName { get; set; }

In your case, I would assume you only want one attribute allowed per property. In which case, you can access the properties of the custom attribute via:

var tableAttribute= propertyInfo.GetCustomAttribute<TableAttribute>();
Console.Write(tableAttribute.HeaderText);
// Outputs "F. Name" when accessing FirstName
// Outputs "L. Name" when accessing LastName

Upvotes: 7

Jon Skeet
Jon Skeet

Reputation: 1503210

In this case, you'd first retrieve the relevant PropertyInfo, then call MemberInfo.GetCustomAttributes (passing in your attribute type). Cast the result to an array of your attribute type, then get at the HeaderText property as normal. Sample code:

using System;
using System.Reflection;

[AttributeUsage(AttributeTargets.Property)]
public class TableAttribute : Attribute
{
    public string HeaderText { get; set; }
}

public class Person
{
    [Table(HeaderText="F. Name")]
    public string FirstName { get; set; }

    [Table(HeaderText="L. Name")]
    public string LastName { get; set; }
}

public class Test 
{
    public static void Main()
    {
        foreach (var prop in typeof(Person).GetProperties())
        {
            var attrs = (TableAttribute[]) prop.GetCustomAttributes
                (typeof(TableAttribute), false);
            foreach (var attr in attrs)
            {
                Console.WriteLine("{0}: {1}", prop.Name, attr.HeaderText);
            }
        }
    }
}

Upvotes: 38

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