Convert Object Array to another type array using Reflection

Question

I have an object array and I want to convert it to a specific type array. I have the type to convert it into which I get at run time. But I am having a problem doing the actual conversion.

If I use the Convert.ChangeType, I get the error that Object must implement IConvertible

The Array.ConvertAll is template based and requires that I pass the destination type as a template which I only know at run time. I even tried to do use reflection to call this method but I cannot pass the lambda expression as an argument to the MethodInfo.Invoke method.

Any Ideas?

Right I have the following which is not working:

Type convertTo = GetFinalType();
Object[] objArr = GetObjectArray();
var arr = Array.ConvertAll(objArr,elem=> Convert.ChangeType(elem,convertTo));

@Mark: "I get the error that Object must implement IConvertible" — cdhowie
– cdhowie, Commented Dec 2, 2010 at 22:11
The line var arr = Array.ConvertAll(objArr,elem=> Convert.ChangeType(elem,convertTo)); does not compile because it needs the target type as a template e.g Array.ConvertAll<T1,T2>(objArr,elem=> Convert.ChangeType(elem,convertTo)); .. I only have T2 at runtime — shake
– shake, Commented Dec 2, 2010 at 22:16
@shake: What kinds of objects are you storing in this array? — cdhowie
– cdhowie, Commented Dec 2, 2010 at 22:16
Its nothing special .. just a regular class object. I even tried (MyClass[])objArr and get the error {"Unable to cast object of type 'System.Object[]' to type 'MyClass[]'."} — shake
– shake, Commented Dec 2, 2010 at 22:19

Doug · Accepted Answer · 2016-08-22 22:34:52Z

21

Have you tried this?

var finalType = GetFinalType();
var objArr = GetObjectArray();
var arr = Array.CreateInstance(finalType, objArr.Length);
Array.Copy(objArr, arr, objArr.Length);

That's untested, but it should work. It's more compact and doesn't (really) use reflection.

edited Aug 22, 2016 at 22:34

answered Jan 31, 2011 at 23:07

Doug

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1 Comment

shake Over a year ago

You are absolutely right. This is easier. Thanks for the comment. I should have thought of that a long time ago

Mark Avenius · Accepted Answer · 2010-12-02 22:11:20Z

1

You are close; does the following work, or was objType a typo?

Type convertTo = GetFinalType();
Object[] objArr = GetObjectArray();
var arr = Array.ConvertAll(objArr,elem=> Convert.ChangeType(elem, convertTo));

answered Dec 2, 2010 at 22:11

Mark Avenius

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Comments

shake · Accepted Answer · 2010-12-02 23:27:37Z

1

I did it the worst way possible but I managed it somehow. I created a new class

public class Tools
{
    public static T[] Convert<T>(object[] objArr)
    {
        IList<T> list = new List<T>();

        foreach (var o in objArr)
        {
            list.Add((T)o);
        }

        return list.ToArray();
    }
}

And where I needed the conversion, I used:

MethodInfo method = typeof(Tools).GetMethod("Convert");
MethodInfo generic = method.MakeGenericMethod(new Type[] { t });

object o = generic.Invoke(null, new object[] { objArr });

var m =  Convert.ChangeType(o,typeof(tArr));

Where

t = typeof(MyClass); 
tArr = typeof(MyClass[]);

answered Dec 2, 2010 at 23:27

shake

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Comments

cdhowie · Accepted Answer · 2010-12-02 22:19:23Z

0

The code is failing because some object in your array is not a primitive type, or is not something that implements the IConvertible interface You cannot use Convert.ChangeType() on such objects.

edited Dec 2, 2010 at 22:19

answered Dec 2, 2010 at 22:11

cdhowie

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Comments

Bryun · Accepted Answer · 2017-09-12 08:38:27Z

0

This is a solution that worked for me:

public static T[] CastArrayToType<T>(object[] collection)
{
    return Array.ConvertAll<object, T>(
        collection,
        delegate(object prop)
        {
            return (T)prop;
        }
    );
}

answered Sep 12, 2017 at 8:38

Bryun

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