Trying to use reflection to find the first Int32 property of a class

Question

Hi folks,

I'm trying to find the first property of a class that is an Integer .. and get it's value.

So i've got the following code .. which always returns false:

foreach(var property in type.GetProperties(BindingFlags.Public |
    BindingFlags.Instance))
{
    var someType = property.PropertyType is int; // Always false.
}

Why is this / what did I do wrong. This should be really simple :(

/me is having a bad day ...

Answer 1

Change the test to:

var firstInt32Property = property.PropertyType == typeof(int);

This is necessary because the property's property-type is itself not an integer: it is aSystem.Typeobject that (loosely) represents what type the property-getter returns / property-setter accepts. On the other hand, invoking the property getter on an instance of the containing-type will produce an actual integer.

Here's a way to use LINQ instead of the foreach loop:

var firstInt32Property = type.GetProperties(BindingFlags.Public | BindingFlags.Instance)
                             .First(p => p.PropertyType == typeof(int)); 

(This will throw an exception if no such property exists.)

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To retrieve the value of the property from an instance of the containing type:

int value = (int)firstInt32Property.GetValue(myObj, null);

This will of course fail if the 'first' Int32 property happens to be an indexer or indeed if it simply doesn't have a getter. You could filter such properties out on the original query if such scenarios are likely.

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Also note that this code is of limited use because the idea of 'the first property of a class that is an integer' is a little bit suspect. FromType.GetProperties:

The GetPropertiesmethod does not return properties in a particular order, such as alphabetical or declaration order. Your code must not depend on the order in which properties are returned, because that order varies.