Question

Looks like this has been answered for python, but not C#, and since I’m python illiterate and new at C#, here goes:

I’m trying to get a property from a instance of a class (Task/task) based on a enum parameter (type) and add the property to a List. The tricky part is that I’m not sure if the property value is going to be a string or a list of strings.

So, generally I’m looking at something like:

PropertyInfo propertyInfo = typeof(Task).GetProperty(type.ToString());
List<string> values = new List<string>();

then something I know doesn’t work when the value is a List, but illustrates my intent:

values.Add((string)propertyInfo.GetValue(task, null));

What are my options?

Answer 1

You can use PropertyInfo.PropertyType to check the type of the property – or you could just fetch the value as object and go from there:

List<string> values = new List<string>();
object value = propertyInfo.GetValue(task, null);
if (value is string)
{
    values.Add((string) value);
}
else if (value is IEnumerable<string>)
{
    values.AddRange((IEnumerable<string>) value);
}
else
{
    // Do whatever you want if the type doesn't match...
}

Or instead of using is and casting, you can use as and check the result against null:

List<string> values = new List<string>();
object value = propertyInfo.GetValue(task, null);
string stringValue = value as string;
if (stringValue != null)
{
    values.Add(stringValue);
}
else
{
    IEnumerable<string> valueSequence = value as IEnumerable<string>;
    if (valueSequence != null)
    {
        values.AddRange(valueSequence);
    }
    else
    {
        // Do whatever you want if the type doesn't match...
    } 
}

Note that this works if the property is any other sort of sequence of strings, not just a List<string>. It also copies the list, so that any further changes won’t affect the existing list that the property refers to. Adjust if you need to 🙂

One point that Lee’s answer reminded me of – if it’s a string property with a null value and you want a list with a single null element, you’ll need to use PropertyType. For example:

if (propertyInfo.PropertyType == typeof(string))
{
    values.Add((string) propertyInfo.GetValue(task, null));
}