从自定义属性装饰的属性中获取价值? [英] Get value from custom attribute-decorated property?

问题描述

我写了一个自定义属性，用于类的某些成员上

I've written a custom attribute that I use on certain members of a class:

public class Dummy
{
    [MyAttribute]
    public string Foo { get; set; }

    [MyAttribute]
    public int Bar { get; set; }
}

我能够从类型中获取自定义属性并找到我的特定属性.我不知道该怎么做是获取分配的属性的值.当我获取Dummy的一个实例并将其(作为一个对象)传递给我的方法时，如何获取从.GetProperties()返回的PropertyInfo对象并获取分配给.Foo和.Bar的值?

I'm able to get the custom attributes from the type and find my specific attribute. What I can't figure out how to do is to get the values of the assigned properties. When I take an instance of Dummy and pass it (as an object) to my method, how can I take the PropertyInfo object I get back from .GetProperties() and get the values assigned to .Foo and .Bar?

我的问题是我不知道如何正确调用GetValue.

My problem is that I can't figure out how to properly call GetValue.

void TestMethod (object o)
{
    Type t = o.GetType();

    var props = t.GetProperties();
    foreach (var prop in props)
    {
        var propattr = prop.GetCustomAttributes(false);

        object attr = (from row in propattr where row.GetType() == typeof(MyAttribute) select row).First();
        if (attr == null)
            continue;

        MyAttribute myattr = (MyAttribute)attr;

        var value = prop.GetValue(prop, null);
    }
}

但是，当我这样做时，prop.GetValue调用给了我TargetException-对象与目标类型不匹配.如何构造此调用以获取此值?

However, when I do this, the prop.GetValue call gives me a TargetException - Object does not match target type. How do I structure this call to get this value?

推荐答案

您需要将对象本身传递给GetValue，而不是属性对象:

Your need to pass object itself to GetValue, not a property object:

var value = prop.GetValue(o, null);

还有另一件事-您不应使用.First()，而应使用.FirstOrDefault()，因为如果某些属性不包含任何属性，则代码将引发异常:

And one more thing - you should use not .First(), but .FirstOrDefault(), because your code will throw an exception, if some property does not contains any attributes:

object attr = (from row in propattr 
               where row.GetType() == typeof(MyAttribute) 
               select row)
              .FirstOrDefault();

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