CODEWITHSUNDEEP
c#parameter-passing
user5002462
user5002462

Reputation:

C# Custom Attribute parameters

I saw this answer from this link Adding parameters to custom attributes of how is to add parameters on Custom Attribute 

class MyCustomAttribute : Attribute {
    public int[] Values { get; set; }

    public MyCustomAttribute(params int[] values) {
       this.Values = values;
    }
}

[MyCustomAttribute(3, 4, 5)]
class MyClass { }

Now I am wondering if can't it be write like this?

class MyCustomAttribute : Attribute {
    private int[] _values;

    public MyCustomAttribute(params int[] values) {
       _values = values;
    }
}

[MyCustomAttribute(3, 4, 5)]
class MyClass { }

I changed the property Values into a variable _values. I also made it private and it works fine when I tried it.

Can someone enlighten me why the accepted answer is valid?

Upvotes: 14

Views: 55703

Answers (3)

jl_
jl_

Reputation: 5539

There are differences, and it is all about reflection.

Main among them is the fluency that we get - we could either use the constructor or the Values property.

enter image description here

public class MyCustomAttribute : Attribute
{
    public int[] Values { get; set; } = new int[] { 1, 2, 3 };

    public MyCustomAttribute(params int[] values)
    {
        this.Values = values;
    }
}

[MyCustom(1, 2, 3)]
class MyClass
{

}

[MyCustom(Values = new int[] { 1, 2, 3})]
public class MyAnotherClass
{
}

Another factor is reflection to get the property; With the Values field being public, we could use the below to get the details but not with private: 

var data = typeof(MyCustomAttribute).GetProperty("Values");

Upvotes: 6

Ralf Bönning
Ralf Bönning

Reputation: 15445

For [MyCustomAttribute(3, 4, 5)] the parameter list is unnamed, so the the constructor of MyCustomAttribute is used.

Therefore it does not matter, if there is a public Values properties.

In your first code sample it is acceptable to use [MyCustomAttribute(3, 4, 5)] and [MyCustom(Values = new[] {3, 4, 5})].

The second code sample "only" accepts [MyCustomAttribute(3, 4, 5)].

Upvotes: 5

Han
Han

Reputation: 3072

The accepted answer uses the public property instead of a private field. The benefit of public property is you can omit the constructor and supply the values of the properties in the default constructor.

I change your first code, the one with public property, to something like this.

class MyCustomAttribute : Attribute {
    public int[] Values { get; set; }
}

[MyCustomAttribute(Values = new int[] { 3, 4, 5 })]
class MyClass { }

Upvotes: 16

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