Setting value in an array via reflection

Question

Is there a way to set a single value in an array property via reflection in c#?

My property is defined like this:

double[]    Thresholds      { get; set; }

For "normal" properties I use this code to set it via reflection:

PropertyInfo pi = myObject.GetType().GetProperty(nameOfPropertyToSet);
pi.SetValue(myObject, Convert.ChangeType(valueToSet, pi.PropertyType), null);

How would I have to change this code to set the value in an array property at an arbitrary position? Thanks!

BTW: I tried to use the index parameter, but that seems only to work for indexed properties, not properties that are arrays...

Marc Gravell · Accepted Answer · 2012-03-20 08:06:00Z

23

When you do:

obj.Thresholds[i] = value;

that is semantically equivalent to:

double[] tmp = obj.Thresholds;
tmp[i] = value;

which means you don't want a SetValue at all; rather, you want to use GetValue to obtain the array, and then mutate the array. If the type is known to be double[], then:

double[] arr = (double[]) pi.GetValue(myObject, null);
arr[i] = value;

otherwise perhaps the non-generic IList approach (since arrays implement IList):

IList arr = (IList) pi.GetValue(myObject, null);
arr[i] = value;

If it is a multi-dimensional array, you'll have to use Array in place of IList.

answered Mar 20, 2012 at 8:06

Marc Gravell

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Comments

bluish · Accepted Answer · 2014-02-07 16:09:51Z

9

You are not actually setting the property, just changing the property value:

object value = myObject.GetType().GetProperty(nameOfPropertyToset).GetValue(myObject, null);

if (value is Array)
{
    Array arr = (Array)value;
    arr.SetValue(myValue, myIndex);
}
else
{
    ...
}

edited Feb 7, 2014 at 16:09

bluish

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answered Mar 20, 2012 at 8:05

Bas

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1 Comment

Marc Gravell Over a year ago

"changing the property value" is confusing phrasing, as that is synonymous with "setting the property" (directly or indirectly). Actually, the property value here never changes (it is the same reference); it is the array contents that change. Also, GetValue needs a 2nd parameter here.

Alexandre Ricardo Di Primio · Accepted Answer · 2016-11-16 00:16:49Z

Te code here will work for on it, its design to fill a 10 position array, you can do it for any size array.

The function PopulateInstance populate a data structure with what I need.

    object singleval;
    Array arrayval;
    System.Type LocalPType = obj.GetType().GetField(node.Name).FieldType;
    if (LocalPType.IsArray)
    {
        singleval = TreeNodeProperty.CreateNewInstance(LocalPType.GetElementType());
        arrayval =  Array.CreateInstance(LocalPType, 10);
        for(int i = 0; i < 10; i++)
        {
            singleval = PopulateInstance(singleval, node);
            arrayval.SetValue(singleval, i);
        }
        obj.GetType().GetField(node.Name).SetValue(obj, arrayval);
    }
    else
    {
        object val;
        val = Activator.CreateInstance(LocalPType);
        obj.GetType().GetField(node.Name).SetValue(obj,         PopulateInstance(val, node));
    }

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