使用C＃中的“Type”对象键入转换对象

Question

This one has proven to be a little tricky for me so far. I am wondering if it is possible to type cast an object using a System.Type object.

I have illustrated below what I mean:

public interface IDataAdapter
{
    object Transform(object input);
    Type GetOutputType();
}

public class SomeRandomAdapter : IDataAdapter
{
    public object Transform(object input)
    {
        string output;

        // Do some stuff to transform input to output...

        return output;
    }

    public Type GetOutputType()
    {
        return typeof(string);
    }
}

// Later when using the above methods I would like to be able to go...
var output = t.Transform(input) as t.GetOutputType();

The above is a generic interface which is why I am using "object" for the types.

Answer 1

The typical way to do that is to use generics, like so:

public T2 Transform<T, T2>(T input)
{
    T2 output;

    // Do some stuff to transform input to output...

    return output;
}

int    number = 0;
string numberString = t.Transform<int, string>(number);

As you mentioned in your comment below, generics are very similar to C++ Templates. You can find the MSDN documentation for Generics here , and the article " Differences Between C++ Templates and C# Generics (C# Programming Guide) " will probably be helpful.

Finally, I might be misunderstanding what you want to do inside the method body: I'm not sure how you'll transform an arbitrary type T into another arbitrary type T2 , unless you specify constraints on the generic types. For example, you might need to specify that they both have to implement some interface. Constraints on Type Parameters (C# Programming Guide) describes how to do this in C#.

Edit : Given your revised question, I think this answer from Marco M. is correct (that is, I think you should use the Converter delegate where you're currently trying to use your IDataAdapter interface.)

Answer 2

Why make it complicated, when you are sure that it returns a string?

var output = t.Transform(input) as string;

If I have misunderstood what you are saying, here is one more way

var output = Convert.ChangeType(t.Transform(input), t.GetOutputType());

Answer 3

You are better off using something like the Converter delegate

public delegate TOutput Converter<TInput, TOutput>(TInput input);

for an example, check out msdn

public static void Main()
{
    // Create an array of PointF objects.
    PointF[] apf = {
        new PointF(27.8F, 32.62F),
        new PointF(99.3F, 147.273F),
        new PointF(7.5F, 1412.2F) };

    // Display each element in the PointF array.
    Console.WriteLine();
    foreach( PointF p in apf )
        Console.WriteLine(p);

    // Convert each PointF element to a Point object.
    Point[] ap = Array.ConvertAll(apf, 
        new Converter<PointF, Point>(PointFToPoint));

    // Display each element in the Point array.
    Console.WriteLine();
    foreach( Point p in ap )
    {
        Console.WriteLine(p);
    }
}

public static Point PointFToPoint(PointF pf)
{
    return new Point(((int) pf.X), ((int) pf.Y));
}

Answer 4

The above is a generic interface which is why I am using "object" for the types

Would it not make more sense to use an actual generic interface:

public U Transform<T, U>(T input)
{
    string output;

    return output;
}

U output = t.Transform(input) as U;

Answer 5

This is what I have gone with (based off the IEnumerable structure):

public interface IDataAdapter
{
    object Transform(object input);
}

public interface IDataAdapter<OutT, InT> : IDataAdapter
{
    OutT Transform(InT input);
}

public class SomeClass : IDataAdapter<string, string>
{
    public string Transform(string input)
    {
        // Do something...
    }

    public object Transform(object input)
    {
        throw new NotImplementedException();
    }
}