Reputation: 81

C# interface question

If I want a bunch of classes to implement a method, I can just make them implement an interface. However, if I want the method to always be decorated with two custom attributes, if there a syntax for that? In other words, I want every class that implement method Run() to attach a descriptionAttribute and a versionAttribute.

Update: Is there a way to make classes that implement Run() generate a compile error if they did not attach the two attributes?

Upvotes: 7

Answers (5)

chilltemp

Reputation: 8960

You could use an abstract class to validate the attributes when the class is initialized.

abstract class MustImpliment
{
    protected MustImpliment()
    {
        object[] attributes = this.GetType().GetCustomAttributes(typeof(DescriptionAttribute), true);

        if (attributes == null || attributes.Length == 0)
            throw new NotImplementedException("Pick a better exception");
    }

    // Must impliment DescriptionAttribute
    public abstract void DoSomething();
}

class DidntImpliment : MustImpliment
{
    public override void DoSomething()
    {
        // ...
    }
}

Update: This will not cause a compiler error, but you can use this as part of a Unit Test as Jerod Houghtelling suggested.

Upvotes: 0

hunter

Reputation: 63552

public interface IRun
{
    void Run();
}

public abstract class RunBase : IRun
{
    [Description("Run Run Run")]
    [Version("1.0")]
    public abstract void Run();
}

public abstract class SoRunning : RunBase
{
    public override void Run() {} 
}

you should be able to get the Attributes off of the base class

Upvotes: 6

Jerod Houghtelling

Reputation: 4867

I don't think there is built in compile time support. However one way you could get around this is to create a program or script that is ran at compile time by using the projects build events.

For example:

Create a small program that through the commandline will take in a file path to an assembly.
Make the program load the assembly from the command line
Get all types out of the assembly
Verify that all of the types that implement your interface have the attributes set
Have the program throw an exception if conditions are not met otherwise it runs successfully
Add the program to the post-build event commands through the project properties

Note: This could also be done as a 'unit' test.

Upvotes: 1