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NameObjectCollectionBase.BaseHasKeys Method

Gets a value indicating whether the NameObjectCollectionBase instance contains entries whose keys are not a null reference (Nothing in Visual Basic).

[Visual Basic]
Protected Function BaseHasKeys() As Boolean
[C#]
protected bool BaseHasKeys();
[C++]
protected: bool BaseHasKeys();
[JScript]
protected function BaseHasKeys() : Boolean;

Return Value

true if the NameObjectCollectionBase instance contains entries whose keys are not a null reference (Nothing in Visual Basic); otherwise, false.

Example

[Visual Basic, C#, C++] The following code example uses BaseHasKeys to determine if the collection contains keys that are not a null reference (Nothing in Visual Basic).

[Visual Basic] 
Imports System
Imports System.Collections
Imports System.Collections.Specialized

Public Class MyCollection
   Inherits NameObjectCollectionBase

   Private _de As New DictionaryEntry()

   ' Gets a key-and-value pair (DictionaryEntry) using an index.
   Default Public ReadOnly Property Item(index As Integer) As DictionaryEntry
      Get
         _de.Key = Me.BaseGetKey(index)
         _de.Value = Me.BaseGet(index)
         Return _de
      End Get
   End Property

   ' Creates an empty collection.
   Public Sub New()
   End Sub 'New

   ' Adds an entry to the collection.
   Public Sub Add(key As [String], value As [Object])
      Me.BaseAdd(key, value)
   End Sub 'Add

   ' Gets a value indicating whether the collection contains keys that are not a null reference.
   Public ReadOnly Property HasKeys() As [Boolean]
      Get
         Return Me.BaseHasKeys()
      End Get
   End Property

End Class 'MyCollection


Public Class SamplesNameObjectCollectionBase   

   Public Shared Sub Main()

      ' Creates an empty MyCollection instance.
      Dim myCol As New MyCollection()
      Console.WriteLine("Initial state of the collection (Count = {0}):", myCol.Count)
      PrintKeysAndValues(myCol)
      Console.WriteLine("HasKeys? {0}", myCol.HasKeys)

      Console.WriteLine()

      ' Adds an item to the collection.
      myCol.Add("blue", "sky")
      Console.WriteLine("Initial state of the collection (Count = {0}):", myCol.Count)
      PrintKeysAndValues(myCol)
      Console.WriteLine("HasKeys? {0}", myCol.HasKeys)

   End Sub 'Main

   Public Shared Sub PrintKeysAndValues(myCol As MyCollection)
      Dim i As Integer
      For i = 0 To myCol.Count - 1
         Console.WriteLine("[{0}] : {1}, {2}", i, myCol(i).Key, myCol(i).Value)
      Next i
   End Sub 'PrintKeysAndValues

End Class 'SamplesNameObjectCollectionBase 


'This code produces the following output.
'
'Initial state of the collection (Count = 0):
'HasKeys? False
'
'Initial state of the collection (Count = 1):
'[0] : blue, sky
'HasKeys? True


[C#] 
using System;
using System.Collections;
using System.Collections.Specialized;

public class MyCollection : NameObjectCollectionBase  {

   private DictionaryEntry _de = new DictionaryEntry();

   // Gets a key-and-value pair (DictionaryEntry) using an index.
   public DictionaryEntry this[ int index ]  {
      get  {
         _de.Key = this.BaseGetKey( index );
         _de.Value = this.BaseGet( index );
         return( _de );
      }
   }

   // Creates an empty collection.
   public MyCollection()  {
   }

   // Adds an entry to the collection.
   public void Add( String key, Object value )  {
      this.BaseAdd( key, value );
   }

   // Gets a value indicating whether the collection contains keys that are not a null reference.
   public Boolean HasKeys  {
      get  {
         return( this.BaseHasKeys() );
      }
   }

}

public class SamplesNameObjectCollectionBase  {

   public static void Main()  {

      // Creates an empty MyCollection instance.
      MyCollection myCol = new MyCollection();
      Console.WriteLine( "Initial state of the collection (Count = {0}):", myCol.Count );
      PrintKeysAndValues( myCol );
      Console.WriteLine( "HasKeys? {0}", myCol.HasKeys );

      Console.WriteLine();

      // Adds an item to the collection.
      myCol.Add( "blue", "sky" );
      Console.WriteLine( "Initial state of the collection (Count = {0}):", myCol.Count );
      PrintKeysAndValues( myCol );
      Console.WriteLine( "HasKeys? {0}", myCol.HasKeys );

   }

   public static void PrintKeysAndValues( MyCollection myCol )  {
      for ( int i = 0; i < myCol.Count; i++ )  {
         Console.WriteLine( "[{0}] : {1}, {2}", i, myCol[i].Key, myCol[i].Value );
      }
   }

}


/*
This code produces the following output.

Initial state of the collection (Count = 0):
HasKeys? False

Initial state of the collection (Count = 1):
[0] : blue, sky
HasKeys? True

*/

[C++] 
#using <mscorlib.dll>
#using <system.dll>

using namespace System;
using namespace System::Collections;
using namespace System::Collections::Specialized;

public __gc class MyCollection : public NameObjectCollectionBase
{
private:
   DictionaryEntry _de;

public:
   // Gets a key-and-value pair (DictionaryEntry) using an index.
   __property DictionaryEntry get_Item( int index )
   {
      _de.Key = this->BaseGetKey(index);
      _de.Value = this->BaseGet(index);
      return(_de);
   }

   // Creates an empty collection.
   MyCollection()
   {
   }

   // Adds an entry to the collection.
   void Add(String* key, Object* value)
   {
      this->BaseAdd(key, value);
   }

   // Gets a value indicating whether the collection contains keys that are not a 0 reference.
   __property Boolean get_HasKeys()
   {
      return(this->BaseHasKeys());
   }

};

void PrintKeysAndValues(MyCollection* myCol) {
   for (int i = 0; i < myCol->Count; i++) {
      Console::WriteLine(S"[{0}] : {1}, {2}", __box(i), myCol->Item[i].Key, myCol->Item[i].Value);
   }
}

int main() 
{
   // Creates an empty MyCollection instance.
   MyCollection* myCol = new MyCollection();
   Console::WriteLine(S"Initial state of the collection (Count = {0}):", __box(myCol->Count));
   PrintKeysAndValues(myCol);
   Console::WriteLine(S"HasKeys? {0}", __box(myCol->HasKeys));

   Console::WriteLine();

   // Adds an item to the collection.
   myCol->Add(S"blue", S"sky");
   Console::WriteLine(S"Initial state of the collection (Count = {0}):", __box(myCol->Count));
   PrintKeysAndValues(myCol);
   Console::WriteLine(S"HasKeys? {0}", __box(myCol->HasKeys));
}

/*
This code produces the following output.

Initial state of the collection (Count = 0):
HasKeys? False

Initial state of the collection (Count = 1):
[0] : blue, sky
HasKeys? True

*/

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework

See Also

NameObjectCollectionBase Class | NameObjectCollectionBase Members | System.Collections.Specialized Namespace

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