Question

I want to do this:

[AttributeUsage(AttributeTargets.Property, 
                Inherited = false, 
                AllowMultiple = true)]
sealed class MyAttribute : Attribute
{
    readonly string showName;
    readonly Type controlType;

    public Type ControlType
    {
        get { return controlType; }
    } 

    readonly Func<Control, object> selector;

    public Func<Control, object> Selector
    {
        get { return selector; }
    } 


    public MyAttribute(string showName, 
                       Type controlType, 
                       Func<Control, object> selector)
    {
        this.showName = showName;
        this.controlType = controlType;
        this.selector = selector;
    }

    public string ShowName
    {
        get { return showName; }
    }

}
class Foo
{
    // problem. Do you have an idea?
    [My("id number", 
     typeof(NumericUpDown), 
     Convert.ToInt32(control=>((NumericUpDown)control).Value))] 
    public int Id { get; set; }
}

I want to do attribute that contains name, type of control, and selector for take from the control the value of the property.

I try do it, and can’t.

Answer 1

No, you cannot use an anonymous method or lambda expression in an attribute decoration.

Incidentally, if you could, it would be (moving the control declaration):

control=>Convert.ToInt32(((NumericUpDown)control).Value)

But… You can’t. Either use the string name of a method that you resolve with reflection, or use something like a subclass of the attribute class with a virtual method override instead.