在VBA中实现多个接口的接口

Question

我想创建一个实现多个接口的接口，然后创建一个实现该接口的类。例如：

有效模块：

Public Sub Fly()
End Sub

Public Function GetAltitude() As Long
End Function

ISwimmable模块：

Public Sub Swim()
End Sub

Public Function GetDepth() As Long
End Function

IFlySwim模块：

Implements IFlyable
Implements ISwimmable

Public Sub IFlyable_Fly()
End Sub

Public Function IFlyable_GetAltitude() As Long
End Function    

Public Sub ISwimmable_Swim()
End Sub

Public Function ISwimmable_GetDepth() As Long
End Function

这全部编译正常。但是，如果我声明了IFlySwim类型的Object，则VBA中的预测性文本会给我：

并且试图创建实现IFlySwimmable的类是行不通的。

鸭类：

Implements IFlySwim

Public Sub IFlySwim_IFlyable_Fly()
    Debug.Print "Flying with wings!"
End Sub

Public Function IFlySwim_IFlyable_GetAltitude() As Long
    IFlySwim_IFlyable_GetAltitude = 30
End Function

Public Sub IFlySwim_ISwimmable_Swim()
    Debug.Print "Swimming with feet!"
End Sub

Public Function IFlySwim_ISwimmable_GetDepth() As Long
    IFlySwim_ISwimmable_GetDepth = 20
End Function

按下编译按钮会给我错误：“编译错误：对象模块需要为接口“ IFlySwim”实现“ IFlyable_Fly”。

因此，这使我相信Implement在另一个接口中创建一个接口是行不通的。至少，从VBA的角度来看，这没有任何意义。这是可以理解的，因为我实际上并未在IFlyable中提供ISwimmable和IFlySwim的实现。我真正想做的是将IFlyable和ISwimmable的实现推迟到同时实现两者的类中进行。

现在，如果我的Duck类是：

Implements IFlyable
Implements ISwimmable

Public Sub IFlyable_Fly()
    Debug.Print "Flying with wings!"
End Sub

Public Function IFlyable_GetAltitude() As Long
    IFlyable_GetAltitude = 30
End Function

Public Sub ISwimmable_Swim()
    Debug.Print "Swimming with feet!"
End Sub

Public Function ISwimmable_GetDepth() As Long
    ISwimmable_GetDepth = 20
End Function

然后，当我使用它时，预测性下拉菜单会给我：

我可以将Duck强制转换为IFlyable或ISwimmable以这样使用：

但是如果我想创建一个接受Flyable / Swimable的Function或Sub怎么办？我是否需要创建一个完全独立的接口IFlySwim，其中包含IFlyable和ISwimmable中的所有子功能，然后将我的Duck类修改为仅从IFlySwim中实现？

Answer 1

不幸的是，这就是通过组合继承的方式。但是，您应该认识到Duck类将接口与函数实现的具体实现绑定在一起。您需要使用第二个间接级别

Implements IFlyable
Implements ISwimmable

Private Sub IFlyable_Fly()
    Fly
End Sub

|Private Function IFlyable_GetAltitude() As Long
    IFlyable_GetAltitude=GetAltitude
End Function

Private Sub ISwimmable_Swim()
    Swim
End Sub

Private Function ISwimmable_GetDepth() As Long
    ISwimmable=GetDepth
End Function

Public Sub Fly()
    Debug.Print "Flying with wings!"
End Sub

Public Function GetAltitude() As Long
    GetAltitude = 30
End Function

Public Sub Swim()
    Debug.Print "Swimming with feet!"
End Sub

Public Function GetDepth() As Long
    GetDepth = 20
End Function

由此，您可以看到GetAltitude和GetDepth都可以引用VerticalPosition的属性

Private Function IFlyable_GetAltitude() As Long
        IFlyable_GetAltitude=GetVerticalPosition
End Function


Private Function ISwimmable_GetDepth() As Long
    ISwimmable_GetDepth=- GetVerticalPosition
End function

可能对您有帮助或对您没有帮助。

Answer 2

接口方法/属性（即以下划线为前缀的方法/属性）不应公开。必须实现它们以实现派生类中接口的约定，但应将它们标记为私有。完成后，您可以使用诸如Fly或GetAltitude的方法名称公开公共成员（请参见下文）：

Option Explicit

Implements ISwimmable
Implements IFlyable

'********************************************************
'Public Methods
'********************************************************
Public Function GetDepth() As Long

    GetDepth = 10

End Function

Public Sub Swim()

    Debug.Print "Swimming!"

End Sub

Public Function GetAltitude() As Long

    GetAltitude = 50

End Function


Public Sub Fly()

    Debug.Print "Flying with wings!"

End Sub


'********************************************************
'Private Methods
'********************************************************
Private Function ISwimmable_GetDepth() As Long
End Function

Private Sub ISwimmable_Swim()
End Sub


Private Function IFlyable_GetAltitude() As Long
End Function

Private Sub IFlyable_Fly()
End Sub

并且您的测试代码将变为以下内容：（见下文）

Sub InterfaceTest()

    Dim ducky As New Duck

    ducky.Fly
    Debug.Print ducky.GetAltitude()

    ducky.Swim
    Debug.Print ducky.GetDepth()

End Sub

但是如果我想创建一个接受Flyable / Swimable的Function或Sub怎么办？我是否需要创建一个完全独立的接口IFlySwim，其中包含IFlyable和ISwimmable的所有Sub / Function，然后将Duck类修改为仅从IFlySwim实现？

简短回答：是的。

为什么？

因为，VBA / VB6不完全支持继承。要执行您的要求，您将创建一个继承自ISwimmable和IFlyable的第三个类，然后在其他类中实现该类。

使用像C#这样的完全面向对象的语言，您可以执行以下操作：（请参见下文）

public interface IFlyable   {

    void Fly(); 
    int GetAltitude(); 

} 


public interface ISwimmable {

    void Swim();
    int GetDepth();

} 

//Base Class
public abstract class BaseDuck: ISwimmable, IFlyable    {

    public BaseDuck(){}

    public void Fly()   {

        Console.WriteLine("Flying with wings!"); 

    } 

    public virtual int GetAltitude()    {

        return 50; 

    } 

    public void Swim()  {

        Console.WriteLine("Swimming!"); 

    } 

    public virtual int GetDepth()   {

        return 10; 

    } 


}

//Derived Class
public class SeaDuck: BaseDuck  {

    public SeaDuck(){}

    public override int GetAltitude()   {

        return 50; 

    } 

    public override int GetDepth()  {

        return 100; 

    } 

    public void RideWaves() {

        Console.WriteLine("Riding waves!");

    }

}

//Derived Class
public class MallardDuck: BaseDuck  {

    public MallardDuck(){}

    public override int GetAltitude()   {

        return 100; 

    } 

    public override int GetDepth()  {

        return 10; 

    } 

    public void HeadToLandForWinter()   {

        Console.WriteLine("Headed for land!");

    }

}

使用以下内容进行测试：（请参见下文）

using System;

public class Program
{
    public static void Main()
    {
        SeaDuck seaDuck = new SeaDuck();

        Console.WriteLine("Sea Duck:");
        seaDuck.Fly();
        Console.WriteLine(seaDuck.GetAltitude().ToString()); 

        seaDuck.Swim();
        Console.WriteLine(seaDuck.GetDepth().ToString()); 

        seaDuck.RideWaves(); 

        Console.WriteLine("\n");

        Console.WriteLine("Mallard Duck:");
        MallardDuck mallardDuck = new MallardDuck();
        mallardDuck.Fly();
        Console.WriteLine(mallardDuck.GetAltitude().ToString()); 

        mallardDuck.Swim();
        Console.WriteLine(mallardDuck.GetDepth().ToString()); 

        mallardDuck.HeadToLandForWinter();

    }
}

产品：

Sea Duck:
Flying with wings!
50
Swimming!
100
Riding waves!


Mallard Duck:
Flying with wings!
100
Swimming!
10
Headed for land!