How to set property value using Expressions? [duplicate]

Question

Given the following method:

public static void SetPropertyValue(object target, string propName, object value) {     var propInfo = target.GetType().GetProperty(propName,                          BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.DeclaredOnly);      if (propInfo == null)         throw new ArgumentOutOfRangeException("propName", "Property not found on target");     else         propInfo.SetValue(target, value, null); } 

How would you go about writing it's expression enabled equivalent without needing to pass in an extra parameter for target?

Why do this instead of setting the property directly I can hear you say. For example suppose we have the following class with a property that has a public getter but private setter:

public class Customer  {    public string Title {get; private set;}    public string Name {get; set;} } 

I would like to be able to call:

var myCustomerInstance = new Customer(); SetPropertyValue<Customer>(cust => myCustomerInstance.Title, "Mr"); 

Now here is some sample code.

public static void SetPropertyValue<T>(Expression<Func<T, Object>> memberLamda , object value) {     MemberExpression memberSelectorExpression;     var selectorExpression = memberLamda.Body;     var castExpression = selectorExpression as UnaryExpression;      if (castExpression != null)         memberSelectorExpression = castExpression.Operand as MemberExpression;     else         memberSelectorExpression = memberLamda.Body as MemberExpression;      // How do I get the value of myCustomerInstance so that I can invoke SetValue passing it in as a param? Is it possible  } 

Any pointers?

Answer 1

You could cheat and make life easier with an extension method:

public static class LambdaExtensions {     public static void SetPropertyValue<T, TValue>(this T target, Expression<Func<T, TValue>> memberLamda, TValue value)     {         var memberSelectorExpression = memberLamda.Body as MemberExpression;         if (memberSelectorExpression != null)         {             var property = memberSelectorExpression.Member as PropertyInfo;             if (property != null)             {                 property.SetValue(target, value, null);             }         }     } } 

and then:

var myCustomerInstance = new Customer(); myCustomerInstance.SetPropertyValue(c => c.Title, "Mr"); 

The reason why this is easier is because you already have the target on which the extension method is invoked. Also the lambda expression is a simple member expression without closures. In your original example the target is captured in a closure and it could be a bit tricky to get to the underlying target and PropertyInfo.