How to find out if a property is an auto-implemented property with reflection?

Question

So in my case i am doing discovery of the structure of a class using reflection. I need to be able to find out if a property is an auto-implemented property by the PropertyInfo object. I assume that the reflection API does not expose such functionality because auto-properties are C# dependent, but is there any workaround to get this information?

Answer 1

You could check to see if the get or set method is marked with the CompilerGenerated attribute. You could then combine that with looking for a private field that is marked with the CompilerGenerated attribute containing the name of the property and the string "BackingField".

Perhaps:

public static bool MightBeCouldBeMaybeAutoGeneratedInstanceProperty(     this PropertyInfo info ) {     bool mightBe = info.GetGetMethod()                        .GetCustomAttributes(                            typeof(CompilerGeneratedAttribute),                            true                        )                        .Any();     if (!mightBe) {         return false;     }       bool maybe = info.DeclaringType                      .GetFields(BindingFlags.NonPublic | BindingFlags.Instance)                      .Where(f => f.Name.Contains(info.Name))                      .Where(f => f.Name.Contains("BackingField"))                      .Where(                          f => f.GetCustomAttributes(                              typeof(CompilerGeneratedAttribute),                              true                          ).Any()                      )                      .Any();          return maybe;     } 

It's not fool proof, quite brittle and probably not portable to, say, Mono.

Answer 2

This should do:

public static bool IsAutoProperty(this PropertyInfo prop) {     return prop.DeclaringType.GetFields(BindingFlags.NonPublic | BindingFlags.Instance)                              .Any(f => f.Name.Contains("<" + prop.Name + ">")); } 

The reason is that for auto-properties the Name property of the backing FieldInfo would look like:

<PropertName>k__BackingField 

Since characters < and > wouldn't appear for normal fields, a field with that kind of naming points to a backing field of an auto-property. As Jason says, its brittle still.

Or to make it a tad faster,

public static bool IsAutoProperty(this PropertyInfo prop) {     if (!prop.CanWrite || !prop.CanRead)         return false;      return prop.DeclaringType.GetFields(BindingFlags.NonPublic | BindingFlags.Instance)                              .Any(f => f.Name.Contains("<" + prop.Name + ">")); }