在C#中，屬性（Attributes）是一種將元數(shù)據(jù)與代碼元素關(guān)聯(lián)的方式，它們提供了可在運(yùn)行時(shí)通過反射查詢的附加信息，並在元編程中起關(guān)鍵作用。 1. 屬性通過方括號(hào)應(yīng)用於目標(biāo)元素，例如標(biāo)記方法為已過時(shí)；2. 可通過繼承System.Attribute創(chuàng)建自定義屬性，如為類添加描述信息；3. 使用反射可動(dòng)態(tài)讀取屬性內(nèi)容，這對(duì)於構(gòu)建序列化器、ORM或測(cè)試運(yùn)行器等系統(tǒng)非常有用；4. 屬性常用於標(biāo)記需忽略序列化的成員、標(biāo)註單元測(cè)試方法、定義Web API模型驗(yàn)證規(guī)則等場(chǎng)景；5. 在元編程中，屬性結(jié)合反射支持插件自動(dòng)檢測(cè)、依賴注入管理及ASP.NET MVC的路由和授權(quán)等功能；6. 由於反射性能較低，頻繁操作時(shí)應(yīng)考慮緩存以提升效率。因此，儘管屬性本身小巧，但它們使現(xiàn)代C#開發(fā)更加靈活且易於維護(hù)。

In C#, attributes are a way to associate metadata with code elements like classes, methods, properties, or even assemblies. They provide additional information that can be queried at runtime using reflection, and they play a key role in metaprogramming—where code inspects and modifies its own structure or behavior dynamically.

What Do Attributes Look Like in C#?

An attribute is applied using square brackets just before the target element. For example:

 [Obsolete("Use the new version instead.")]
public void OldMethod()
{
    // Method implementation
}

Here, Obsolete is an attribute built into the .NET framework that tells the compiler this method shouldn't be used anymore.

You can also create your own custom attributes by inheriting from System.Attribute . Here's a basic example:

 public class MyCustomAttribute : Attribute
{
    public string Description { get; }

    public MyCustomAttribute(string description)
    {
        Description = description;
    }
}

[MyCustom("This is a sample class")]
public class SampleClass
{
    // Class body
}

Now, SampleClass has some extra info attached to it via the MyCustom attribute.

How to Use Reflection to Access Attributes

Reflection lets you inspect types, methods, and other members at runtime. Combined with attributes, it becomes a powerful tool for dynamic behavior.

Let's say you want to read the MyCustom attribute from SampleClass . Here's how you might do that:

 var type = typeof(SampleClass);
var attr = (MyCustomAttribute)Attribute.GetCustomAttribute(
    type,
    typeof(MyCustomAttribute));

if (attr != null)
{
    Console.WriteLine(attr.Description); // Outputs: This is a sample class
}

This kind of pattern is useful when building systems like serializers, ORMs, or test runners that need to make decisions based on metadata rather than hardcoded logic.

Some common use cases include:

• Marking methods to be ignored during serialization
• Annotating test methods in unit testing frameworks
• Defining validation rules for models in web APIs

Using Attributes in Metaprogramming Scenarios

Metaprogramming refers to writing code that manipulates or generates other code. While C# isn't as flexible as languages like Ruby or Python in this area, attributes combined with reflection allow for a fair amount of dynamic behavior.

For instance, imagine you're building a plugin system where certain classes should be auto-detected and registered. You could define an attribute like [Plugin] , apply it to relevant classes, and then scan all loaded assemblies at startup for types marked with that attribute.

Another example is dependency injection containers that look for [Service] or [Scoped] attributes to determine how to manage object lifetimes.

Even tools like ASP.NET MVC use attributes heavily—for routing, authorization, model binding, etc.

One thing to keep in mind is performance. Reflection isn't blazing fast, so if you're scanning many types or doing it frequently, caching results can help avoid slowdowns.

Attributes Are Simple but Powerful Tools

They may seem small and unassuming, but attributes are a big part of what makes modern C# development flexible and maintainable. Whether you're using them out-of-the-box or creating your own, they let you add declarative information that drives behavior behind the scenes.

Used wisely, they reduce boilerplate and separate concerns—like keeping configuration close to the code it affects.

So next time you see something like [Authorize] or [JsonProperty] , remember: there's a good chance reflection and attributes working together under the hood.

That's basically it.

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