如何使用表达式设置属性值？ [英] How to set property value using Expressions?

问题描述

给定以下方法：

  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，在目标上找不到属性）; 
 else 
 propInfo.SetValue（target，value，null）; 
} 
  

你如何去写它的表达式启用相当于不需要传入额外的目标参数？

为什么不直接设置属性，我可以听到你说的话。例如，假设我们有一个具有public getter但是私有setter的属性的类：

  public class Customer 
 {
 public string Title {get; private set;} 
 public string Name {get;我想要能够调用：
  var myCustomerInstance = new Customer（）; 
 SetPropertyValue< Customer>（cust => myCustomerInstance.Title，Mr）; 
  
现在这里是一些示例代码。 
  public static void SetPropertyValue< T>（表达式< Func< T，Object>> memberLamda，对象值）
 {
 MemberExpression memberSelectorExpression; 
 var selectorExpression = memberLamda.Body; 
 var castExpression = selectorExpression为UnaryExpression; 
 
 if（castExpression！= null）
 memberSelectorExpression = castExpression.Operand作为MemberExpression; 
 else 
 memberSelectorExpression = memberLamda.Body as MemberExpression; 
 
 //如何获取myCustomerInstance的值，以便我可以调用SetValue作为参数传递它？是否可能
 
} 
  
任何指针？ 
解决方案
您可以通过扩展方法欺骗并使生活更轻松：
  public static class LambdaExtensions 
 {
 public static void SetPropertyValue< T，TValue>（this T target，Expression< Func< T，TValue> TValue值）
 {
 var memberSelectorExpression = memberLamda.Body as MemberExpression; 
 if（memberSelectorExpression！= null）
 {
 var property = memberSelectorExpression.Member as PropertyInfo; 
 if（property！= null）
 {
 property.SetValue（target，value，null）; 
} 
} 
} 
} 
  
然后：
  var myCustomerInstance = new Customer（）; 
 myCustomerInstance.SetPropertyValue（c => c.Title，Mr）; 
  
为什么这更容易的原因是因为已经有扩展方法被调用的目标。 lambda表达式也是一个没有闭包的简单成员表达式。在你的原始示例中，目标被捕获在一个关闭中，它可能有点棘手得到基础目标和 PropertyInfo 。
 
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? 
解决方案
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.

                        
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