但是对于只是简单的SetValue或者GetValue，包括用反射构造函数，我们可以想一个中继的方法，那就是使用表达式树。对于不理解表达式树的，可以到微软文档查看，点击我。表达式树很容易通过对象模型表示表达式，因此强烈建议学习。查看以下代码：
static void Main()
{
Dog dog = new Dog();
PropertyInfo propertyInfo = dog.GetType().GetProperty(nameof(dog.Name)); //获取对象Dog的属性
MethodInfo SetterMethodInfo = propertyInfo.GetSetMethod(); //获取属性Name的set方法
ParameterExpression param = Expression.Parameter(typeof(Dog), "param");
Expression GetPropertyValueExp = Expression.Lambda(Expression.Property(param, nameof(dog.Name)), param);
Expression<Func<Dog, String>> GetPropertyValueLambda = (Expression<Func<Dog, String>>)GetPropertyValueExp;
ParameterExpression paramo = Expression.Parameter(typeof(Dog), "param");
ParameterExpression parami = Expression.Parameter(typeof(String), "newvalue");
MethodCallExpression MethodCallSetterOfProperty = Expression.Call(paramo, SetterMethodInfo, parami);
Expression SetPropertyValueExp = Expression.Lambda(MethodCallSetterOfProperty, paramo, parami);
Expression<Action<Dog, String>> SetPropertyValueLambda = (Expression<Action<Dog, String>>)SetPropertyValueExp;
//创建了属性Name的Get方法表达式和Set方法表达式,当然只是最简单的
Func<Dog, String> Getter = GetPropertyValueLambda.Compile();
Action<Dog, String> Setter = SetPropertyValueLambda.Compile();
Setter?.Invoke(dog, "WLJ"); //我们现在对dog这个对象的Name属性赋值
String dogName = Getter?.Invoke(dog); //获取属性Name的值
Console.WriteLine(dogName);
Console.ReadKey();
}
public class Dog
{
public String Name { get; set; }
}
以下代码可能很难看得懂，但只要知道我们创建了属性的Get、Set这两个方法就行，其结果最后也能输出狗的名字 WLJ,拥有ExpressionTree的好处是他有一个名为Compile（）的方法，它创建一个代表表达式的代码块。现在是最有趣的部分，假设你在编译时不知道类型（在这篇文章中包含的代码我在不同的程序集上创建了一个类型）你仍然可以应用这种技术，我将对于常用的属性的set，get操作进行分装。
/// <summary>
/// 属性类，仿造反射中的PropertyInfo
/// </summary>
public class Property
{
private readonly PropertyGetter getter;
private readonly PropertySetter setter;
public String Name { get; private set; }
public PropertyInfo Info { get; private set; }
public Property(PropertyInfo propertyInfo)
{
if (propertyInfo == null)
throw new NullReferenceException("属性不能为空");
this.Name = propertyInfo.Name;
this.Info = propertyInfo;
if (this.Info.CanRead)
{
this.getter = new PropertyGetter(propertyInfo);
}
if (this.Info.CanWrite)
{
this.setter = new PropertySetter(propertyInfo);
}
}
/// <summary>
/// 获取对象的值
/// </summary>
/// <param name="instance"></param>
/// <returns></returns>
public Object GetValue(Object instance)
{
return getter?.Invoke(instance);
}
/// <summary>
/// 赋值操作
/// </summary>
/// <param name="instance"></param>
/// <param name="value"></param>
public void SetValue(Object instance, Object value)
{
this.setter?.Invoke(instance, value);
}
private static readonly ConcurrentDictionary<Type, Core.Reflection.Property[]> securityCache = new ConcurrentDictionary<Type, Property[]>();
public static Core.Reflection.Property[] GetProperties(Type type)
{
return securityCache.GetOrAdd(type, t => t.GetProperties().Select(p => new Property(p)).ToArray());
}
}
/// <summary>
/// 属性Get操作类
/// </summary>
public class PropertyGetter
{
private readonly Func<Object, Object> funcGet;
public PropertyGetter(PropertyInfo propertyInfo) : this(propertyInfo?.DeclaringType, propertyInfo.Name)
{
}
public PropertyGetter(Type declareType, String propertyName)
{
if (declareType == null)
{
throw new ArgumentNullException(nameof(declareType));
}
if (propertyName == null)
{
throw new ArgumentNullException(nameof(propertyName));
}
this.funcGet = CreateGetValueDeleagte(declareType, propertyName);
}
//代码核心部分
private static Func<Object, Object> CreateGetValueDeleagte(Type declareType, String propertyName)
{
// (object instance) => (object)((declaringType)instance).propertyName
var param_instance = Expression.Parameter(typeof(Object));
var body_objToType = Expression.Convert(param_instance, declareType);
var body_getTypeProperty = Expression.Property(body_objToType, propertyName);
var body_return = Expression.Convert(body_getTypeProperty, typeof(Object));
return Expression.Lambda<Func<Object, Object>>(body_return, param_instance).Compile();
}
public Object Invoke(Object instance)
{
return this.funcGet?.Invoke(instance);
}
}
public class PropertySetter
{
private readonly Action<Object, Object> setFunc;
public PropertySetter(PropertyInfo property)
{
if (property == null)
{
throw new ArgumentNullException(nameof(property));
}
this.setFunc = CreateSetValueDelagate(property);
}
private static Action<Object, Object> CreateSetValueDelagate(PropertyInfo property)
{
// (object instance, object value) =>
// ((instanceType)instance).Set_XXX((propertyType)value)
//声明方法需要的参数
var param_instance = Expression.Parameter(typeof(Object));
var param_value = Expression.Parameter(typeof(Object));
var body_instance = Expression.Convert(param_instance, property.DeclaringType);
var body_value = Expression.Convert(param_value, property.PropertyType);
var body_call = Expression.Call(body_instance, property.GetSetMethod(), body_value);
return Expression.Lambda<Action<Object, Object>>(body_call, param_instance, param_value).Compile();
}
public void Invoke(Object instance, Object value)
{
this.setFunc?.Invoke(instance, value);
}
}
