How Can I Dynamically Add Validation Attributes to Properties in C#?

Adding Attributes to Properties Dynamically

This code sample demonstrates how to add validation attributes to properties at runtime. It leverages reflection to access the property's FillAttributes method and inject the desired attribute.

Code Analysis

// Get PropertyDescriptor object for the given property name
var propDesc = TypeDescriptor.GetProperties(typeof(T))[propName];

// Get FillAttributes methodinfo delegate
var methodInfo = propDesc.GetType().GetMethods(BindingFlags.Instance | BindingFlags.Public |
                                                      BindingFlags.NonPublic)
    .FirstOrDefault(m => m.IsFamily || m.IsPublic && m.Name == "FillAttributes");

// Create Validation attribute
var attribute = new RequiredAttribute();
var attributes = new ValidationAttribute[] { attribute };

// Invoke FillAttribute method
methodInfo.Invoke(propDesc, new object[] { attributes });

Exception Analysis

However, upon execution, you may encounter the "Collection was of a fixed size" exception. This occurs because the property's validation attributes collection is defined as a fixed-size array. To address this, we need to replace the existing array with a new, larger one.

Solution

To resolve this issue, you can implement a custom attribute caching system to store and apply attributes dynamically. An example implementation could be:

// Initialize cache dictionary and synchronization mechanism
private static readonly Dictionary<Type, Attribute[]> AttributeCache = new Dictionary<Type, Attribute[]>();
private static readonly object SyncObject = new object();

protected override Attribute[] GetCustomAttributes(Type attributeType, bool inherit)
{
    if (AttributeCache.TryGetValue(this.GetType(), out Attribute[] cachedAttrs))
    {
        return cachedAttrs;
    }
    else
    {
        lock (SyncObject)
        {
            if (!AttributeCache.TryGetValue(this.GetType(), out cachedAttrs))
            {
                cachedAttrs = base.GetCustomAttributes(attributeType, inherit);
                AttributeCache.Add(this.GetType(), cachedAttrs);
            }
        }
        return cachedAttrs;
    }
}

With this custom caching mechanism, the code will successfully add validation attributes to properties at runtime without causing the fixed-size collection exception.

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