How to get a property value using Reflection if the property name is defined as "name"

Question

I have the following code to compare two collections to one another...

    //code invocation
    CollectionComparer comp = new CollectionComparer("name", "ASC");
    this.InnerList.Sort(comp);

class

public class CollectionComparer : IComparer
{
    private String _property;
    private String _order;

    public CollectionComparer(String Property, String Order)
    {
        this._property = Property;
        this._order = Order;
    }

    public int Compare(object obj1, object obj2)
    {
        int returnValue;

        Type type = obj1.GetType();
        PropertyInfo propertie1 = type.GetProperty(_property); // returns null here
        Type type2 = obj2.GetType();
        PropertyInfo propertie2 = type2.GetProperty(_property); // returns null here

        object finalObj1 = propertie1.GetValue(obj1, null); // Null Reference Exception thrown here, because propertie1 is null
        object finalObj2 = propertie2.GetValue(obj2, null);

        IComparable Ic1 = finalObj1 as IComparable;
        IComparable Ic2 = finalObj2 as IComparable;

        if (_order == "ASC")
        {
            returnValue = Ic1.CompareTo(Ic2);
        }
        else
        {
            returnValue = Ic2.CompareTo(Ic1);
        }

        return returnValue;
    }
}

The code seems to work fine, except when I try to sort a property called "name". When comparing that property both the variables propertie1 and propertie2 are null, and the code throws an exception because of that.

So my question is how to use reflection to get the value of a property with the name of "name"?

The exception is a null reference message... I'll update my code accordingly... — bastos.sergio, Jan 25 '16 at 10:37
Show the POCO definition of the type you are comparing, nothing wrong with the reflection code? — Janne Matikainen, Jan 25 '16 at 10:48
Where is `name`? Show how its defined. Or simply use proper [`GetProperty` overload](https://msdn.microsoft.com/en-us/library/system.type.getproperty(v=vs.110).aspx) yourself, because you are either messing with `BindingFlags` or maybe even trying to get `field` value? — Sinatr, Jan 25 '16 at 10:48
How does the actual class looks like `obj1` is an instance from? — MakePeaceGreatAgain, Jan 25 '16 at 10:48

score 0 · Answer 1 · answered Jan 25 '16 at 10:37

By the way, is _property variable set?

How about this extension method:

public static object GetProperty(this object instance, string name)
    {
        if (instance == null)
            throw new ArgumentNullException("instance");

        if (name == null)
            throw new ArgumentNullException("name");

        Type type = instance.GetType();
        PropertyInfo property = type.GetProperty(name, BindingFlags.Public | BindingFlags.Instance);

        if (property == null)
            throw new InvalidOperationException(string.Format("Type {0} does not have a property {1}", type, name));

        object result = property.GetValue(instance, null);

        return result;
    }

I've already tried changing the bindingflags to this `type.GetProperty(name, BindingFlags.Public | BindingFlags.Instance);` and I still get a null reference — bastos.sergio, Jan 25 '16 at 10:46
And what objects are you passing in to the Compare method? Do they have the "name" property — Tamas Ionut, Jan 25 '16 at 10:47

score 0 · Accepted Answer · answered Jan 25 '16 at 10:57

Ok, I figured it out... I guess uppercase counts when doing reflection...

I needed to change the code invocation to...

//code invocation
CollectionComparer comp = new CollectionComparer("Name", "ASC");
this.InnerList.Sort(comp);

As the property was actually called "Name" and not "name"

How to get a property value using Reflection if the property name is defined as "name"

2 Answers2