Making a generic property

Question

I have a class that stores a serialized value and a type. I want to have a property/method returning the value alredy casted:

property string Value { get; set; }
property Type TheType { get; set; }
property typeof(TheType) CastedValue{ get {return Convert.ChangeType(Value, typeof(_Type)); }

Is this posible in C#?

Answer 1

It's possible if the class containing the property is generic, and you declare the property using the generic parameter:

class Foo<TValue> {
    public string Value { get; set; }
    public TValue TypedValue {
        get {
            return (TValue)Convert.ChangeType(Value, tyepof(TValue));
        }
    }
}

An alternative would be to use a generic method instead:

class Foo {
    public string Value { get; set; }
    public Type TheType { get; set; }

    public T CastValue<T>() {
         return (T)Convert.ChangeType(Value, typeof(T));
    }
}

You can also use the System.ComponentModel.TypeConverter classes to convert, since they allow a class to define it's own converter.

Edit: note that when calling the generic method, you must specify the generic type parameter, since the compiler has no way to infer it:

Foo foo = new Foo();
foo.Value = "100";
foo.Type = typeof(int);

int c = foo.CastValue<int>();

You have to know the type at compile time. If you don't know the type at compile time then you must be storing it in an object, in which case you can add the following property to the Foo class:

public object ConvertedValue {
    get {
        return Convert.ChangeType(Value, Type);
    }
}

Answer 2

I don't believe the example you've given here is possible. The type of CastedValue has to be defined at compile time, which means it can't depend on a runtime value (the value of the TheType property).

EDIT: Brannon's solution has some good ideas for how to handle this using a generic function rather than a property.

Answer 3

Properties, events, constructors etc can't be generic - only methods and types can be generic. Most of the time that's not a problem, but I agree that sometimes it's a pain. Brannon's answer gives two reasonable workarounds.

Answer 4

Thanks Brannon, the method itself works fine, but now my problem is calling it. Unless i know the type in the caller it does not compile: private void Form1_Load(object sender, EventArgs e) { int i =85; string s = i.ToString(); Type ty = i.GetType(); int c = CastedValue(s, ty); MessageBox.Show(sum(c).ToString()); } public T CastedValue(string Value, Type tt) { return (T)Convert.ChangeType(Value, tt); }

If I try with this:

int c = CastedValue(s, ty);

I then get the following error at compile time: "Cannot implicitly convert type 'ty' to 'int'"