C# Reflection Indexed Properties

问题:

I am writing a Clone method using reflection. How do I detect that a property is an indexed property using reflection? For example:

public string[] Items
{
   get;
   set;
}

My method so far:

public static T Clone<T>(T from, List<string> propertiesToIgnore) where T : new()
{
    T to = new T();

    Type myType = from.GetType();

    PropertyInfo[] myProperties = myType.GetProperties();

    for (int i = 0; i < myProperties.Length; i++)
    {
        if (myProperties[i].CanWrite && !propertiesToIgnore.Contains(myProperties[i].Name))
        {
            myProperties[i].SetValue(to,myProperties[i].GetValue(from,null),null);
        }
    }

    return to;
}

回答1:

if (propertyInfo.GetIndexParameters().Length > 0)
{
    // Property is an indexer
}

回答2:

Sorry, but

public string[] Items { get; set; }

is not an indexed property, it's merely of an array type! However the following is:

public string this[int index]
{
    get { ... }
    set { ... }
}

回答3:

What you want is the GetIndexParameters() method. If the array that it returns has more than 0 items, that means it's an indexed property.

See the MSDN documentation for more details.

回答4:

If you call property.GetValue(obj,null), and the property IS indexed, then you will get a parameter count mismatch exception. Better to check whether the property is indexed using GetIndexParameters() and then decide what to do.

回答5:

Here is some code that worked for me:

foreach (PropertyInfo property in obj.GetType().GetProperties())
{
  object value = property.GetValue(obj, null);
  if (value is object[])
  {
    ....
  }
}

P.S. .GetIndexParameters().Length > 0) works for the case described in this article: http://msdn.microsoft.com/en-us/library/b05d59ty.aspx So if you care about the property named Chars for a value of type string, use that, but it does not work for most of the arrays I was interested in, including, I am pretty sure, a string array from the original question.

回答6:

You can convert the indexer to IEnumerable

    public static IEnumerable<T> AsEnumerable<T>(this object o) where T : class {
        var list = new List<T>();
        System.Reflection.PropertyInfo indexerProperty = null;
        foreach (System.Reflection.PropertyInfo pi in o.GetType().GetProperties()) {
            if (pi.GetIndexParameters().Length > 0) {
                indexerProperty = pi;
                break;
            }
        }

        if (indexerProperty.IsNotNull()) {
            var len = o.GetPropertyValue<int>("Length");
            for (int i = 0; i < len; i++) {
                var item = indexerProperty.GetValue(o, new object[]{i});
                if (item.IsNotNull()) {
                    var itemObject = item as T;
                    if (itemObject.IsNotNull()) {
                        list.Add(itemObject);
                    }
                }
            }
        }

        return list;
    }


    public static bool IsNotNull(this object o) {
        return o != null;
    }

    public static T GetPropertyValue<T>(this object source, string property) {
        if (source == null)
            throw new ArgumentNullException("source");

        var sourceType = source.GetType();
        var sourceProperties = sourceType.GetProperties();
        var properties = sourceProperties
            .Where(s => s.Name.Equals(property));
        if (properties.Count() == 0) {
            sourceProperties = sourceType.GetProperties(BindingFlags.Instance | BindingFlags.NonPublic);
            properties = sourceProperties.Where(s => s.Name.Equals(property));
        }

        if (properties.Count() > 0) {
            var propertyValue = properties
                .Select(s => s.GetValue(source, null))
                .FirstOrDefault();

            return propertyValue != null ? (T)propertyValue : default(T);
        }

        return default(T);
    }