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

问题描述

 公共静态无效SetPropertyValue（对象的目标，字符串作为propName，对象的值）
：考虑下面的方法
 {
 VAR propInfo = target.GetType（）的getProperty（作为propName，
 BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic可| BindingFlags.DeclaredOnly）。 
 
如果（propInfo == NULL）
抛出新ArgumentOutOfRangeException（作为propName，没有目标找到物业）; 
，否则
 propInfo.SetValue（目标，价值，NULL）; 
} 
  

您会如何去写它的表情启用相当于无需在传递对目标额外的参数？

为什么这样做，而不是设置属性直接我能听到你说。例如，假设我们有一个具有公共的getter但私人二传手属性下面的类：

 公共类客户
 {
公共字符串名称{搞定;私人集;} 
公共字符串名称{;设置;} 
} 
  

我希望能够调用：

  VAR myCustomerInstance =新客户（）; 
 SetPropertyValue<客户>（卡斯特= GT; myCustomerInstance.Title，先生）; 
  

现在这里是一些示例代码。

 公共静态无效SetPropertyValue< T>（表达式来; Func键< T，对象>> memberLamda，对象的值）
 {
 MemberExpression memberSelectorExpression; 
 VAR selectorExpression = memberLamda.Body; 
 VAR castExpression = selectorExpression为UnaryExpression; 
 
如果（castExpression！= NULL）
 memberSelectorExpression = castExpression.Operand为MemberExpression; 
，否则
 memberSelectorExpression = memberLamda.Body为MemberExpression; 
 
 //我如何获得myCustomerInstance的值，这样我可以调用的SetValue在把它当作一个参数？是否有可能
 
} 
  

任何指针？

解决方案

您能欺骗，让生活更容易使用的扩展方法：

 公共静态类LambdaExtensions 
 {
公共静态无效SetPropertyValue< T>（这件T目标，表达< Func键< T，对象>> memberLamda，对象值）
 {
 VAR memberSelectorExpression = memberLamda.Body为MemberExpression; 
如果（！memberSelectorExpression = NULL）
 {
 VAR财产= memberSelectorExpression.Member为的PropertyInfo; 
如果（财产！= NULL）
 {
 property.SetValue（目标，价值，NULL）; 
} 
} 
} 
} 
  

和那么：

  VAR myCustomerInstance =新客户（）; 
 myCustomerInstance.SetPropertyValue（C => c.Title，先生）; 
  

之所以这样是比较容易的，因为你已经在其上调用扩展方法的对象。另外，lambda表达式是不封闭的简单成员表达式。在你原来的例子目标是在封闭拍摄的，它可能是一个有点虽然拿到底层目标和的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>(this T target, Expression<Func<T, object>> memberLamda, object 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 though to get to the underlying target and PropertyInfo.

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