c#-使用表达式树设置字段值
作者:互联网
我需要为一个类中的所有字段创建一个表达式.
因此,我已根据需要采用了this post:
public static void Sample()
{
var setters = GetFieldSetterExpressions<Account>();
var myAccount = new Account();
setters["AccounHolder"](myAccount, "Giovanni");
setters["Pin"](myAccount, 123);
}
public static Dictionary<string, Action<T, object>> GetFieldSetterExpressions<T>() where T: class
{
var dic = new Dictionary<string,Action<T,object>>();
var type = typeof(T);
var fields = type.GetFields();
foreach (var fieldInfo in fields)
{
Type fieldType;
if (IsNullableType(fieldInfo.FieldType))
fieldType = Nullable.GetUnderlyingType(fieldInfo.FieldType);
else
fieldType = fieldInfo.FieldType;
ParameterExpression targetExp = Expression.Parameter(type, "target");
ParameterExpression valueExp = Expression.Parameter(fieldType, "value");
MemberExpression fieldExp = Expression.Field(targetExp, fieldInfo);
BinaryExpression assingExp = Expression.Assign(fieldExp, valueExp);
var setter = Expression.Lambda<Action<T, object>>(assingExp, targetExp, valueExp).Compile();
dic.Add(fieldInfo.Name, setter);
}
return dic;
}
我的问题是Expression.Lambda< Action< T,object>>(..),因为该字段可以是例如字符串,所以我得到了一个例外.
我试图将Expression.Convert转换为我的代码段,但不知道如何实现它.
我该如何在我的代码中集成转换部分?
解决方法:
表达式< Action< T,对象>表示当您的代码使用propertyType时,第二个参数应为object类型.应该是这样的:
var type = typeof(T);
var fields = type.GetFields();
foreach (var fieldInfo in fields)
{
var targetExp = Expression.Parameter(type, "target");
var valueExp = Expression.Parameter(typeof(object), "value");
var fieldExp = Expression.Field(targetExp, fieldInfo);
var assignExp = Expression.Assign(fieldExp, Expression.Convert(valueExp, fieldExp.Type));
var setter = Expression.Lambda<Action<T, object>>(assignExp, targetExp, valueExp).Compile();
}
标签:c,net,expression-trees 来源: https://codeday.me/bug/20191118/2029925.html