[英]Get DateTime value From FieldInfo
I am tryning to retrieve a DateTime
via reflection.我正在尝试通过反射检索DateTime
。 The value is not inside a class or a static class, but it is from a lambda expression
...该值不在 class 或 static class 内,但它来自lambda expression
...
I have this really simple lambda expression: ATest => ATest.MyDate == DateTime.Now
我有这个非常简单的 lambda 表达式: ATest => ATest.MyDate == DateTime.Now
Now, via an ExpressionVisitor
I am trying getting datetime value:现在,通过ExpressionVisitor
我正在尝试获取日期时间值:
public class ExpressionComparionsVisitor : ExpressionVisitor
{
public Expression Modify(Expression expression)
{
return base.Visit(expression);
}
protected override Expression VisitMember(MemberExpression node)
{
if (node.NodeType == ExpressionType.MemberAccess)
{
if (node.Member.MemberType == System.Reflection.MemberTypes.Field)
{
if (node.Type == typeof(DateTime))
{
System.Reflection.FieldInfo fieldInfo = node.Member as System.Reflection.FieldInfo;
if (fieldInfo != null)
{
//Here what I have tried, but no success
//var n = (DateTime)fieldInfo.GetValue(fieldInfo);
//var n = (DateTime)fieldInfo.GetValue(typeof(DateTime));
//var n = (DateTime)fieldInfo.GetValue(node.Member);
//var n = (DateTime)fieldInfo.GetValue(null);
}
}
}
}
return base.VisitMember(node);
}
}
How can I get the DateTime value of that field?如何获取该字段的 DateTime 值? Thank you谢谢
In short you can't.简而言之,你不能。 Your lambda ATest => ATest.MyDate == DateTime.Now
represents a function that accepts a parameter ( ATest
) and returns boolean based on equality ATest.MyDate
to DateTime.Now
, so the value of ATest.MyDate
can different for different provided inputs. Your lambda ATest => ATest.MyDate == DateTime.Now
represents a function that accepts a parameter ( ATest
) and returns boolean based on equality ATest.MyDate
to DateTime.Now
, so the value of ATest.MyDate
can different for different provided inputs . To get some concrete value you need to provide some concrete input:要获得一些具体的价值,您需要提供一些具体的输入:
class MyClass {public DateTime MyDate;}
var someVal = new MyClass { MyDate = new DateTime(2020, 01, 01) };
Expression<Func<MyClass, bool>> expr = ATest => ATest.MyDate == DateTime.Now;
var node = (expr.Body as BinaryExpression).Left as MemberExpression;
var fi = node.Member as FieldInfo;
Console.WriteLine(fi.GetValue(someVal)); // prints 1 January of 2020 in corresponding format
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