问题描述:

Is there a typedef equivalent in C#, or someway to get some sort of similar behaviour? I've done some googling, but everywhere I look seems to be negative. Currently I have a situation similar to the following:

class GenericClass<T>

{

public event EventHandler<EventData> MyEvent;

public class EventData : EventArgs { /* snip */ }

// ... snip

}

Now, it doesn't take a rocket scientist to figure out that this can very quickly lead to a lot of typing (apologies for the horrible pun) when trying to implement a handler for that event. It'd end up being something like this:

GenericClass<int> gcInt = new GenericClass<int>;

gcInt.MyEvent += new EventHandler<GenericClass<int>.EventData>(gcInt_MyEvent);

// ...

private void gcInt_MyEvent(object sender, GenericClass<int>.EventData e)

{

throw new NotImplementedException();

}

Except, in my case, I was already using a complex type, not just an int. It'd be nice if it were possible to simplify this a little...

Edit: ie. perhaps typedefing the EventHandler instead of needing to redefine it to get similar behaviour.

网友答案:

No, there's no equivalent of typedef. You can use 'using' directives within one file, e.g.

using CustomerList = System.Collections.Generic.List<Customer>;

but that will only impact that source file.

Fortunately, the example you give does have a fix - implicit method group conversion. You can change your event subscription line to just:

gcInt.MyEvent += gcInt_MyEvent;

:)

网友答案:

Jon really gave a nice solution, I didn't know you could do that!

At times what I resorted to was inheriting from the class and creating its constructors. E.g.

public class FooList : List<Foo> { ... }

Not the best solution (unless your assembly gets used by other people), but it works.

网友答案:

If you know what you're doing, you can define a class with implicit operators to convert between the alias class and the actual class.

class TypedefString // Example with a string "typedef"
{
    private string Value = "";
    public static implicit operator string(TypedefString ts)
    {
        return ((ts == null) ? null : ts.Value);
    }
    public static implicit operator TypedefString(string val)
    {
        return new TypedefString { Value = val };
    }
}

I don't actually endorse this and haven't ever used something like this, but this could probably work for some specific circumstances.

网友答案:

I think there is no typedef. You could only define a specific delegate type instead of the generic one in the GenericClass, i.e.

public delegate GenericHandler EventHandler<EventData>

This would make it shorter. But what about the following suggestion:

Use Visual Studio. This way, when you typed

gcInt.MyEvent += 

it already provides the complete event handler signature from Intellisense. Press TAB and it's there. Accept the generated handler name or change it, and then press TAB again to auto-generate the handler stub.

网友答案:

C# supports some inherited covariance for event delegates, so a method like this:

void LowestCommonHander( object sender, EventArgs e ) { ... } 

Can be used to subscribe to your event, no explicit cast required

gcInt.MyEvent += LowestCommonHander;

You can even use lambda syntax and the intellisense will all be done for you:

gcInt.MyEvent += (sender, e) =>
{
    e. //you'll get correct intellisense here
};
网友答案:

You can use an open source library and NuGet package called LikeType that I created that will give you the GenericClass<int> behavior that you're looking for.

The code would look like:

public class SomeInt : LikeType<int>
{
    public SomeInt(int value) : base(value) { }
}

[TestClass]
public class HashSetExample
{
    [TestMethod]
    public void Contains_WhenInstanceAdded_ReturnsTrueWhenTestedWithDifferentInstanceHavingSameValue()
    {
        var myInt = new SomeInt(42);
        var myIntCopy = new SomeInt(42);
        var otherInt = new SomeInt(4111);

        Assert.IsTrue(myInt == myIntCopy);
        Assert.IsFalse(myInt.Equals(otherInt));

        var mySet = new HashSet<SomeInt>();
        mySet.Add(myInt);

        Assert.IsTrue(mySet.Contains(myIntCopy));
    }
}
网友答案:

Here is the code for it, enjoy!, I picked that up from the dotNetReference type the "using" statement inside the namespace line 106 http://referencesource.microsoft.com/#mscorlib/microsoft/win32/win32native.cs

using System;
using System.Collections.Generic;
namespace UsingStatement
{
    using Typedeffed = System.Int32;
    using TypeDeffed2 = List<string>;
    class Program
    {
        static void Main(string[] args)
        {
        Typedeffed numericVal = 5;
        Console.WriteLine(numericVal++);

        TypeDeffed2 things = new TypeDeffed2 { "whatever"};
        }
    }
}
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