C# - 通过反射枚举自定义属性

Question

这是我的属性定义:

[AttributeUsage(AttributeTargets.Field)]
public class Optional : System.Attribute
{
    public Optional()
    {
    }
}

在我的类(class)中:

[Optional] public TextBox Name;

最后在另一个函数中:

typeof(MyClass).GetFields().ToList<FieldInfo>().ForEach(x => writer.WriteLine(
   x.FieldType + " is called " + 
   x.Name + " and has attributes " + 
   x.GetCustomAttributes(true)[0]
 ));

问题是我收到索引 0 的错误。我只想检查应用该属性的字段。当我删除 x.GetCustomAttributes(true)[0] 时，错误消失了。

确切错误:

异常详细信息:System.IndexOutOfRangeException:索引超出数组范围。

来源错误:

Line 63:             }
Line 64: 
Line 65:             typeof(T).GetFields().ToList<FieldInfo>().ForEach(x => writer.WriteLine(x.FieldType + " is called " + 
Line 66:                 x.Name + " and has attributes " + 
Line 67:                 x.GetCustomAttributes(true)[0]+ "</br>"));

Answer 1

这里似乎有两个问题。要查找具有 [Optional] 属性的所有字段，您需要:

typeof(MyClass).GetFields().Where(
   f => f.GetCustomAttributes(typeof(OptionalAttribute), true).Any())

要在所有字段上写出自定义属性，您需要:

typeof(MyClass).ToList<FieldInfo>().ForEach(x => 
{
 writer.WriteLine(
   x.FieldType + " is called " + 
   x.Name + " and has attributes " + 
   string.Join(", ", x.GetCustomAttributes(true).Select(a => a.ToString()).ToArray()));
});