Getting the type of a MemberInfo with reflection

Question

I'm using reflection to load a treeview with the class structure of a project. Each of the members in a class have a custom attribute assigned to them.

I don't have a problem getting the attributes for a class using MemberInfo.GetCustomAttributes() however I need a way of working out if a class member is a custom class and then needs parsing itself to return the custom attributes.

So far, my code is:

MemberInfo[] membersInfo = typeof(Project).GetProperties();

foreach (MemberInfo memberInfo in membersInfo)
{
    foreach (object attribute in memberInfo.GetCustomAttributes(true))
    {
        // Get the custom attribute of the class and store on the treeview
        if (attribute is ReportAttribute)
        {
            if (((ReportAttribute)attribute).FriendlyName.Length > 0)
            {
               treeItem.Items.Add(new TreeViewItem() { Header = ((ReportAttribute)attribute).FriendlyName });
            }
        }
        // PROBLEM HERE : I need to work out if the object is a specific type
        //                and then use reflection to get the structure and attributes.
    }
}

Is there an easy way of getting the target type of a MemberInfo instance so I can handle it appropriately? I feel I'm missing something obvious but I'm going round in circles at the minute.

score 74 · Answer 1 · answered Apr 16 '13 at 17:39

I think you can get better performance if you carry around this extension method:

public static Type GetUnderlyingType(this MemberInfo member)
{
    switch (member.MemberType)
    {
        case MemberTypes.Event:
            return ((EventInfo)member).EventHandlerType;
        case MemberTypes.Field:
            return ((FieldInfo)member).FieldType;
        case MemberTypes.Method:
            return ((MethodInfo)member).ReturnType;
        case MemberTypes.Property:
            return ((PropertyInfo)member).PropertyType;
        default:
            throw new ArgumentException
            (
             "Input MemberInfo must be if type EventInfo, FieldInfo, MethodInfo, or PropertyInfo"
            );
    }
}

Should work for any MemberInfo, not just PropertyInfo. You may avoid MethodInfo from that list since its not under lying type per se (but return type).

In your case:

foreach (MemberInfo memberInfo in membersInfo)
{
    foreach (object attribute in memberInfo.GetCustomAttributes(true))
    {
        if (attribute is ReportAttribute)
        {
            if (((ReportAttribute)attribute).FriendlyName.Length > 0)
            {
               treeItem.Items.Add(new TreeViewItem() { Header = ((ReportAttribute)attribute).FriendlyName });
            }
        }

        //if memberInfo.GetUnderlyingType() == specificType ? proceed...
    }
}

I wonder why this hasn't been part of BCL by default.

I like this! Always felt a bit fishy casting, even when I knew it was a `PropertyInfo`. — Daniel Park, Feb 24 '15 at 12:03
I'm getting an Exception when memberInfo comes from a MemberExpression.Member, it's a Property but it can't be casted — Daniel, Aug 12 '21 at 19:37
@Daniel looks like a UnaryExpression stands in between. You will have to type check for UnaryExpression and if so take its Operand property. Better to make it a separate question. — nawfal, Sep 23 '21 at 09:08

score 13 · Accepted Answer · answered Apr 10 '13 at 09:14

13

GetProperties returns an array of PropertyInfo so you should use that.
Then it is simply a matter of using the PropertyType property.

PropertyInfo[] propertyInfos = typeof(Project).GetProperties();

foreach (PropertyInfo propertyInfo in propertyInfos)
{
    // ...
    if(propertyInfo.PropertyType == typeof(MyCustomClass))
        // ...
}

answered Apr 10 '13 at 09:14

Daniel Hilgarth

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5

yeah, the `MemberInfo[] membersInfo = ` is a bad sign. One of the reasons I like `var` - less things to get wrong. – Marc Gravell Apr 10 '13 at 09:15

Getting the type of a MemberInfo with reflection

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