Attributes on Field in Class

问题

I want to get a list of fields with an Attribute Sync.Field on each of the field in the class. The field can / cannot have the attribute of Sync.Field

I have been trying the following, but having trouble getting the custom attribute for each field.

FieldInfo[] fiClass = typClass.GetFields();

FieldInfo[] lst = fiClass
                   .Where(c => c.CustomAttribute().GetType() == typeOf(Sync.Field))
                   .ToList();

回答1:

I have a generic collection class, which uses a data class to match an SNMP table with data class fields. Like JsonProperty matches deserialised values to properties. In the same way I define a SNMPPropertyAttribute. The attribute itself is

[AttributeUsage(AttributeTargets.Property, Inherited = false, AllowMultiple = false)]
  sealed class SNMPPropertyAttribute : Attribute
  {
    public SNMPPropertyAttribute(string propertyOID) => PropertyOID = new ObjectIdentifier(propertyOID);

    public ObjectIdentifier PropertyOID { get; }
  }

When in the table constructor, I'm making a dictionary of data fiels and their OIDs from the attribute:

public SNMPTableEntity()
    {
      snmpPoperties = new Dictionary<ObjectIdentifier, PropertyInfo>();
      foreach (PropertyInfo myProperty in GetType().GetProperties(BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public))
      {
        CustomAttributeData snmpAttribure = myProperty.CustomAttributes.Where(x => x.AttributeType == typeof(SNMPPropertyAttribute)).FirstOrDefault();
        if (snmpAttribure != null)
          snmpPoperties.Add(new ObjectIdentifier((string)snmpAttribure.ConstructorArguments[0].Value), myProperty);
      }
    }

It looks similar to what are you trying to acheive, so hopefully it helps. But the difference, is that I'm using properties, not fields. Not sure if it makes a big difference, but...

There is an example of using:

  public class InterfaceTableEntity : SNMPTableEntity
  {
    /// <summary>
    /// A unique value for each interface.  Its value ranges between 1 and the value of ifNumber.  The value for each interface must remain constant at least from one re-initialization of the entity's network management system to the next re- initialization.
    /// </summary>
    [SNMPProperty("1.3.6.1.2.1.2.2.1.1")]
    protected Integer32 ifIndex { get; set; }
    /// <summary>
    /// A textual string containing information about the interface.  This string should include the name of the manufacturer, the product name and the version of the hardware interface.
    /// </summary>
    [SNMPProperty("1.3.6.1.2.1.2.2.1.2")]
    protected OctetString ifDescr { get; set; }
    /// <summary>
    /// The type of interface, distinguished according to the physical/link protocol(s) immediately `below' the network layer in the protocol stack.
    /// </summary>
    [SNMPProperty("1.3.6.1.2.1.2.2.1.3")]
    protected Integer32 ifType { get; set; }
}

回答2:

If you have the FieldInfo, you can get an instance of its attribute using this code:

var attr = fieldInfo.GetCustomAttributes().OfType<Sync.FieldAttribute>().SingleOrDefault();

See my example on DotNetFiddle.

来源：https://stackoverflow.com/questions/54877075/attributes-on-field-in-class

标签

reflection