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C++/CLI .NET Support for Collections
 

Introduction to System Collections

In the previous lesson, we saw that, when creating a collection, you should provide a method that allows you to retrieve a member of the collection. You can list the members of an array or a collection through a technique called an enumeration. Enumerating a collection consists of visiting each member of the list, for any reason judged necessary. For example, you can enumerate a collection to display a list of its members. You can enumerate a collection when looking for a member that responds to a certain criterion.

Besides, or instead of, a for loop, the .NET Framework provides another and better support for enumeration. In the C++/CLI language, you can enumerate a collection using the for each operator, but the collection must be prepared for it: you cannot just use for each for any collection. This support is provided through two main interfaces: public IEnumerator and IEnumerable. These two interfaces are defined in the System::Collections namespace. Therefore, if you intend to use them, you can include this namespace in your source file.

Practical Learning Practical Learning: Introducing Built-In Collections
  1. Start Microsoft Visual C++ and create a new CLR Empty Project named BethesdaCarRental1
  2. To create a new class, in the Solution Explorer, right-click BethesdaCarRental1 -> Add -> Class...
  3. In the Templates list, click C++ Class and click Add
  4. Set the Name to CCar and press Enter
  5. Change the Car.h header file as follows:
      
    #pragma once

using namespace System;

public ref class CCar
{
public:
    String ^ TagNumber;
    String ^ Make;
    String ^ Model;
    short    CarYear;
    int      Mileage;
    String ^ Category;
    bool     HasK7Player;
    bool     HasCDPlayer;
    bool     HasDVDPlayer;
    bool     Available;

    CCar ^ Next;

    CCar(void);
};
  6. Access the Car.cpp source file and implement the constructor as follows:
      
    #include "Car.h"

CCar::CCar()
{
    TagNumber    = L"000 000";
    Make         = L"Unknown";
    Model        = L"Unknown";
    CarYear      = 1960;
    Mileage      = 0;
    Category     = L"Unknown";
    HasK7Player  = false;
    HasCDPlayer  = false;
    HasDVDPlayer = false;
    Available    = false;
}
  7. To create a new class, in the Solution Explorer, right-click BethesdaCarRental1 -> Add -> Class...
  8. In the Templates list, click C++ Class and click Add
  9. Set the Name to CInventory and click Finish
  10. Change the Inventory.h header file as follows:
      
    #pragma once

#include "Car.h"

using namespace System;

public ref class CInventory abstract
{
protected:
    int items;

public:
    CInventory(void);
   
    property int Count
    {
        int get() { return items; }
    }

    virtual int Add(CCar ^ obj) = 0;
    virtual CCar ^ Get(int index) = 0;
    virtual bool Delete() = 0;
};
  11. Access the Inventory.cpp source file and change it as follows:
      
    #include "Inventory.h"

CInventory::CInventory(void)
{
    items = 0;
}
  12. To create a new class, in the Class View, right-click BethesdaCarRental1 -> Add -> Class...
  13. In the Templates list, click C++ Class and click Add
  14. Set the Name to CCarInventory and click Finish
  15. Change the CarInventory.h header file as follows:
      
    #pragma once

#include "Inventory.h"
#include "Car.h"

using namespace System;

public ref class CCarInventory : public CInventory
{
public:
    CCar ^ Head;
    CCar ^ Current;
    CCar ^ Inventory;

    virtual int Add(CCar ^ NewCar) override;
    virtual CCar ^ Get(int index) override;
    virtual bool Delete() override;

    CCarInventory(void);
};
  16. Access the CarInventory.cpp source file and change it as follows:
      
    #include "CarInventory.h"

CCarInventory::CCarInventory(void)
{
    Head = nullptr;
}

int CCarInventory::Add(CCar ^ NewCar)
{
    CCar ^ Sample = gcnew CCar;

    Sample = NewCar;
    Sample->Next = Head;
    Head = Sample;
    return items++;
}

CCar ^ CCarInventory::Get(int index)
{
    CCar ^ Current = Head;

    for(int i = Count - 1;
        i > index && Current != nullptr;
        i--)
        Current = Current->Next;
    return Current;
}

bool CCarInventory::Delete()
{
    if (Head == nullptr)
    {
        Console::WriteLine(L"The inventory is empty");
        return false;
    }

    CCar ^ Current;

    Current = Head->Next;
    Head->Next = Current->Next;
    items--;
    return true;
}
  17. Save all  
 
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