要?jiǎng)?chuàng)建自己的C#自定義屬性，首先需定義一個(gè)繼承自System.Attribute的類，接著添加構(gòu)造函數(shù)和屬性，並通過(guò)AttributeUsage指定適用範(fàn)圍，最後通過(guò)反射讀取並使用它們。例如，定義[CustomAuthor("John")]屬性以標(biāo)記代碼作者，應(yīng)用時(shí)使用[CustomAuthor("Alice")]修飾類或方法，隨後通過(guò)Attribute.GetCustomAttribute方法在運(yùn)行時(shí)獲取屬性信息。常見(jiàn)用途包括驗(yàn)證、序列化控制、依賴注入和單元測(cè)試等，建議將屬性邏輯保持輕量，並合理限制其使用範(fàn)圍。

C# attributes let you add metadata or declarative information to your code elements like classes, methods, properties, etc. They're commonly used for things like serialization, validation, logging, and more. You've probably seen them before, like [Serializable] or [Obsolete] . But what if you want to create your own?

Here's how to understand and build your own custom attribute in C#.

What Exactly Is a Custom Attribute?

An attribute is essentially a class that inherits from System.Attribute . When you create your own, you're defining a type that can be attached to various parts of your code to provide additional information at runtime (or compile time).

For example, you might create a [CustomAuthor("John")] attribute to mark who wrote a specific class.

Custom attributes are useful when you want to inspect code structure or behavior through reflection, or when you're building frameworks or libraries that need to respond to metadata.

How to Create a Custom Attribute

Creating a custom attribute is straightforward. Here's how:

1. Define a class that inherits from Attribute
2. Add constructors and properties as needed
3. Apply the attribute to code elements

Here's a simple example:

 [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
public class CustomAuthorAttribute : Attribute
{
    public string AuthorName { get; }

    public CustomAuthorAttribute(string authorName)
    {
        AuthorName = authorName;
    }
}

Now you can use it like this:

 [CustomAuthor("Alice")]
public class MyService
{
    [CustomAuthor("Bob")]
    public void DoWork()
    {
        // Method logic
    }
}

A few notes:

• You can control where the attribute can be applied using [AttributeUsage] .
• You can include multiple parameters or properties.
• The constructor defines what you can set when applying the attribute.

How to Use Custom Attributes in Code

Once you've defined and applied your custom attribute, you'll probably want to access it at runtime. That's where reflection comes in.

Here's how you can check for your [CustomAuthor] attribute on a class or method:

 var type = typeof(MyService);
var classAttribute = (CustomAuthorAttribute)Attribute.GetCustomAttribute(
    type,
    typeof(CustomAuthorAttribute));

Console.WriteLine($"Class author: {classAttribute?.AuthorName}");

var method = type.GetMethod("DoWork");
var methodAttribute = (CustomAuthorAttribute)Attribute.GetCustomAttribute(
    method,
    typeof(CustomAuthorAttribute));

Console.WriteLine($"Method author: {methodAttribute?.AuthorName}");

This is useful in scenarios like:

• Logging or auditing code authors
• Building a plugin system that scans for specific attributes
• Custom validation or behavior based on metadata

Just remember: reflection can be slow, so avoid doing it in performance-critical paths unless you cache the results.

Common Use Cases and Tips

• Validation attributes – Like [Required] or [Range] in ASP.NET
• Serialization control – For example, [JsonProperty("name")] in JSON libraries
• Dependency injection markers – Some frameworks use attributes to auto-register services
• Testing frameworks – Attributes like [Test] or [SetUp] are common in unit testing tools

Tips:

• Keep your attribute logic lightweight – they're metadata, not business logic
• Use AttributeUsage carefully – restrict to only what makes sense
• You can combine attributes with reflection-based services to build extensible systems

So that's the core of custom attributes in C#. You define a class, apply it to code elements, and then use reflection to read and act on it later. It's not complicated once you get the hang of it, but it opens up a lot of possibilities for clean, extensible code design.

基本上就這些.

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