Operation is not valid due to the current state of the object. on .GetBackingfield()

[joergbattermann]

Hey there,

I am playing a little with Mono.Reflection in a .Net 3.5 project to get a Property's BackingField and its attributes. However, the propertyInfo.GetBackingField() method throws an InvalidOperationException... :-/

Sample Code:

var propertyInfos = myObject.GetType().GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);

foreach (var propertyInfo in propertyInfos) { var backingField = propertyInfo.GetBackingField(); // >> throws System.InvalidOperationException }

More details:

Source: "Mono.Reflection" Message: "Operation is not valid due to the current state of the object."

StackTrace: at Mono.Reflection.BackingFieldResolver.GetBackingField(MethodInfo method, ILPattern pattern) at Mono.Reflection.BackingFieldResolver.GetBackingField(PropertyInfo self)

TargetSite: "System.Reflection.FieldInfo GetBackingField(System.Reflection.MethodInfo, Mono.Reflection.ILPattern)"

Any ideas why this is happening?

-J

[jbevain]

It's possible that you're hitting an indexer. Currently GetBackingField works only for traditional properties. Could you paste the code of the property that triggers the exception ?

[joergbattermann]

Oh now that was quick :)

The property & backingfield are the following:

private string _department;

    /// <summary>
    /// Gets or sets the department.
    /// </summary>
    /// <value>The department.</value>
    public string Department
    {
        get
        {
            Activate(ActivationPurpose.Read);
            return _department;
        }
        set
        {
            Activate(ActivationPurpose.Write);
            _department = value;
        }
    }

(it's using db4o's transparent activation mechanism in the Property there)

[jbevain]

GetBackingField reads the IL of the property to find a certain pattern, specific to simple properties. As you have calls to methods in them, they stop being simple properties.

Now, it's possible to write a custom IL pattern to look for. That's your lucky day, I already wrote the pattern for db4o properties here:

http://source.db4o.com/db4o/trunk/db4o.net/Db4objects.Db4o.Linq/Db4objects.Db4o.Linq/CodeAnalysis/ReflectionMethodAnalyser.cs

[joergbattermann]

Nice! Thanks Jean-Baptiste for the quick help!