< C++ .NET Arrays & Collections 11 | Main | C++ .NET Arrays & Collections 13 >

---

 

 

More On Arrays and Collections 12

 

 

What we have in this page?

 

The StringCollection Class ------------Next-------------------- Supplementary Notes: ^ (Handle to Object on Managed Heap), gcnew and for each, in     The StringCollection Class   The StringCollection class, defined in the System::Collections::Specialized namespace represents a collection of strings. The syntax is shown below. [SerializableAttribute] public ref class StringCollection : IList, ICollection, IEnumerable StringCollection lets you access elements by index, and it lets you add, remove, and insert items. Because the StringCollection class implements the ICollection, IEnumerable, and IList interfaces, the class implements the methods associated with those interfaces, so it provides a lot of functionality that you’ve already met, such as Clear, Count, Contains, and CopyTo. In the following brief exercise, you’ll create a StringCollection and see how to use it. StringCollection accepts a null reference (Nothing in Visual Basic) as a valid value and allows duplicate elements. String comparisons are case-sensitive. Elements in this collection can be accessed using an integer index. Indexes in this collection are zero-based.   1.        Open Visual C++/Studio, and create a new CLR Console Application project named StringCollection.

 

2.        Open the StringCollection.cpp source file and try the following long example that demonstrates several of the properties and methods of StringCollection.

// StringCollection.cpp : main project file.

 

#include "stdafx.h"

#using <System.dll>

 

using namespace System;

using namespace System::Collections;

using namespace System::Collections::Specialized;

 

// prototypes...

void PrintValues1(StringCollection^ myCol);

void PrintValues2(StringCollection^ myCol);

void PrintValues3(StringCollection^ myCol);

 

int main(array<System::String ^> ^args)

{

      Console::WriteLine("StringCollection Class Properties and Methods");

      Console::WriteLine();

      // Create and initializes a new StringCollection.

      StringCollection^ myCol = gcnew StringCollection;

      // Add a range of elements from an array to the end of the StringCollection.

      array<String^>^myArr = {"RED","orange","yellow","RED","green","blue","RED","indigo","violet","RED"};

      myCol->AddRange(myArr);

      // Display the contents of the collection using for each. This is the preferred method.

      Console::WriteLine("Displays the elements using for each:");

      PrintValues1(myCol);

      // Display the contents of the collection using the enumerator.

      Console::WriteLine("Displays the elements using the IEnumerator:");

      PrintValues2(myCol);

      // Display the contents of the collection using the Count and Item properties.

      Console::WriteLine( "Displays the elements using the Count and Item properties:" );

      PrintValues3(myCol);

      // Add one element to the end of the StringCollection and insert another at index 3.

      myCol->Add("* white");

      myCol->Insert(3, "* gray");

      Console::WriteLine("After adding \"* white\" to the end and inserting \"* gray\" at index 3:");

      PrintValues1( myCol );

      // Remove one element from the StringCollection.

      myCol->Remove("yellow");

      Console::WriteLine("After removing \"yellow\":");

      PrintValues1(myCol);

      // Remove all occurrences of a value from the StringCollection.

      int i = myCol->IndexOf("RED");

      while (i > -1)

      {

         myCol->RemoveAt(i);

         i = myCol->IndexOf("RED");

      }

      // Verify that all occurrences of "RED" are gone.

      if (myCol->Contains("RED"))

         Console::WriteLine("*** The collection still contains \"RED\".");

      Console::WriteLine("After removing all occurrences of \"RED\":");

      PrintValues1(myCol);

      // Copy the collection to a new array starting at index 0.

      array<String^>^myArr2 = gcnew array<String^>(myCol->Count);

      myCol->CopyTo(myArr2, 0);

      Console::WriteLine("The new array contains:");

      for (i = 0; i < myArr2->Length; i++)

      {

          Console::WriteLine("   [{0}] {1}", i, myArr2[ i ]);

      }

      Console::WriteLine();

      // Clears the entire collection.

      myCol->Clear();

      Console::WriteLine("After clearing the collection:");

      PrintValues1(myCol);

    return 0;

}

 

// Uses the for each statement which hides the complexity

// of the enumerator. The for each statement is the preferred

// way of enumerating the contents of a collection.

void PrintValues1(StringCollection^ myCol)

{

   for each (Object^ obj in myCol)

     Console::WriteLine("   {0}", obj);

   Console::WriteLine();

}

 

// Uses the enumerator.

void PrintValues2(StringCollection^ myCol)

{

   StringEnumerator^ myEnumerator = myCol->GetEnumerator();

   while (myEnumerator->MoveNext())

      Console::WriteLine("   {0}", myEnumerator->Current);

   Console::WriteLine();

}

 

// Uses the Count and Item properties.

void PrintValues3(StringCollection^ myCol)

{

   for (int i = 0; i < myCol->Count; i++)

      Console::WriteLine("   {0}", myCol[ i ]);

   Console::WriteLine();

}

 

 

 

 

Sample Output:

StringCollection Class Properties and Methods

 

Displays the elements using for each:

   RED

   orange

   yellow

   RED

   green

   blue

   RED

   indigo

   violet

   RED

 

Displays the elements using the IEnumerator:

   RED

   orange

   yellow

   RED

   green

   blue

   RED

   indigo

   violet

   RED

 

Displays the elements using the Count and Item properties:

   RED

   orange

   yellow

   RED

   green

   blue

   RED

   indigo

   violet

   RED

 

After adding "* white" to the end and inserting "* gray" at index 3:

   RED

   orange

   yellow

   * gray

   RED

   green

   blue

   RED

   indigo

   violet

   RED

   * white

 

After removing "yellow":

   RED

   orange

   * gray

   RED

   green

   blue

   RED

   indigo

   violet

   RED

   * white

 

After removing all occurrences of "RED":

   orange

   * gray

   green

   blue

   indigo

   violet

   * white

 

The new array contains:

   [0] orange

   [1] * gray

   [2] green

   [3] blue

   [4] indigo

   [5] violet

   [6] * white

 

After clearing the collection:

 

Press any key to continue . . .

 

 

 

 

Unlike ArrayList and SortedList, StringCollection objects are created with no initial capacity and simply grow as more items are added. Because StringCollection implements the ICollection, IList, and IEnumerable interfaces, it supports much of the same functionality as the other classes we’ve discussed, including the ability to use enumerators. The following tables list the members exposed by the StringCollection type.

 

 

 

 

 

 

 

 

 

 

Note: You may find that in C++ .Net the dot (.) is replaced by scope operator (::).

 

 

Part 1 | Part 2 | part 3 | Part 4 | Part 5 | Part 6

 

 

---

 

< C++ .NET Arrays & Collections 11 | Main | C++ .NET Arrays & Collections 13 >