从特定对象的属性/字段获取自定义属性 [英] Get custom attribute from specific object property/field

问题描述

我已经搜索了一段时间，并测试了几种方法，但没有找到想要的答案。我会尝试解释。

I've been searching for a while now and tested several methods, but i didn't find the answer i was looking for. I'll try to explain.

我有一个带有多个字段/属性的对象。这些属性具有自定义属性。
我想要的是从特定属性获取自定义属性，而无需了解对象的全部知识。

I have an object with several fields/properties. These properties have custom attributes. What i want is to get the custom attribute from a specific propertie without all the knowlege of the object.

这是基类

// FieldAttr has a public Text propery

public class TestObject  
{
    // Declare fields
    [FieldAttr("prop_testfld1")]
    public FLDtype1 testfld1 = new FLDtype1();

    [FieldAttr("prop_testfld2")]
    public FLDtype2 testfld2 = new FLDtype2();

    [FieldAttr("prop_testfld3")]
    public FLDtype1 testfld3;
}

public class FLDtype1
{
    public string Value { get; set; }
}

public class FLDtype2
{
    public Guid Value { get; set; }
}

public sealed class FieldAttr: System.Attribute
{
    private string _txt;

    public EntityFieldType(string txt)
    {
        this._text = txt;
    }

    public string Text { get { return this._text; } }
}

我希望能够在我的应用程序中做到这一点：

And i want to be able to do this in my application:

static void Main(string[] args)
{
    TestObject test = new TestObject();

    // (Option 1: preferred)
    Console.WriteLine(test.testfld1.getFieldAttr().Text);

    // (Option 2)
    Console.WriteLine(test.getFieldAttr(test.testfld1).Text);
}

这可能吗？我见过从对象的所有属性/字段中获取自定义属性值的方法，但没有针对特定字段的方法。

Is this possible? I've seen methods to get custom attribute values from all properties/fields of an object, but not for a specific field.

我有一个可行的方法来获取来自枚举的自定义属性，但无法为对象字段/属性重新创建它。这是因为我无法获取要尝试探索的字段的名称，因为（例如）test.testfld1.ToString（）给了我 ns.FLDtype1。

I've got a working method to get custom attribute from an enum, but wasn't able to recreate it for object fields/properties. This is because i couldn't get the name of the field i was trying to explore, because (for example) test.testfld1.ToString() give's me "ns.FLDtype1".

期待答案：）
（请原谅我的英语）

Looking forward for the answer :) (and excuse my english)

推荐答案

反复试验我决定对Selman22答案进行一些修改。这是我创建的代码：

After another day of trial and error I decided to make use of Selman22 answer with a little modification. This is code I created:

public class TestObject : iTestObject 
{
    // Declare fields
    [FieldAttr("prop_testfld1")]
    public FLDtype1 testfld1 = new FLDtype1();

    [FieldAttr("prop_testfld2")]
    public FLDtype2 testfld2 = new FLDtype2();

    [FieldAttr("prop_testfld3")]
    public FLDtype1 testfld3;
}

public class FLDtype1 : iField
{
    public string Value { get; set; }
}

public class FLDtype2 : iField
{
    public Guid Value { get; set; }
}

public sealed class FieldAttr: System.Attribute
{
    private string _txt;

    public FieldAttr(string txt)
    {
        this._txt = txt;
    }

    public string Text { get { return this._txt; } }
}

public interface iField { }
public interface iTestObject { }

public static class Extensions
{
    public static FieldAttr GetFieldAttr<T>(this T source, Expression<Func<iField>> field) where T : iTestObject 
    {
        // Get member body. If no body present, return null
        MemberExpression member = (MemberExpression)field.Body;
        if (member == null) { return null; }

        // Get field info. If no field info present, return null
        FieldInfo fieldType = typeof(T).GetField(member.Member.Name);
        if (fieldType == null) { return null; }

        // Return custom attribute
        return fieldType.GetCustomAttribute<FieldAttr>();
    }
}

用法：

public class Program
{
    public static void Main()
    {
        TestObject test = new TestObject();
        Console.WriteLine(test.GetFieldAttr(() => test.testfld1).Text);
        Console.WriteLine(test.GetFieldAttr(() => test.testfld2).Text);
        Console.WriteLine(test.GetFieldAttr(() => test.testfld3).Text);
    }
}

用途：

using System;
using System.Linq;
using System.Reflection;
using System.Linq.Expressions;

我已经实现了用于保护 GetFieldAttr 方法的接口

I have implemented interfaces to protect the GetFieldAttr method

@ Sulman22：感谢Thnx！

@Sulman22: Thnx for the response!

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