Dictionary<TKey, TValue>.IDictionary.Item Property

Parameters

• key
  Type: System.Object
  The key of the value to get.

Property Value

Type: System.Object
The value associated with the specified key, or nulla null reference (Nothing in Visual Basic) if key is not in the dictionary or key is of a type that is not assignable to the key type TKey of the Dictionary<TKey, TValue>.

Imports System.Collections
Imports System.Collections.Generic

Public Class Example

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      ' Create a new dictionary of strings, with string keys,
      ' and access it using the IDictionary interface.
      '
      Dim openWith As IDictionary = _
          New Dictionary(Of String, String)

      ' Add some elements to the dictionary. There are no 
      ' duplicate keys, but some of the values are duplicates.
      ' IDictionary.Add throws an exception if incorrect types
      ' are supplied for key or value.
      openWith.Add("txt", "notepad.exe")
      openWith.Add("bmp", "paint.exe")
      openWith.Add("dib", "paint.exe")
      openWith.Add("rtf", "wordpad.exe")


...


' The Item property is the default property, so you 
' can omit its name when accessing elements. 
outputBlock.Text &= String.Format("For key = ""rtf"", value = {0}.", _
    openWith("rtf")) & vbCrLf

' The default Item property can be used to change the value
' associated with a key.
openWith("rtf") = "winword.exe"
outputBlock.Text &= String.Format("For key = ""rtf"", value = {0}.", _
    openWith("rtf")) & vbCrLf

' If a key does not exist, setting the default Item property
' for that key adds a new key/value pair.
openWith("doc") = "winword.exe"

' The default Item property returns Nothing if the key
' is of the wrong data type.
outputBlock.Text &= String.Format("The default Item property returns Nothing" _
    & " if the key is of the wrong type:") & vbCrLf
outputBlock.Text &= String.Format("For key = 2, value = {0}.", _
    openWith(2)) & vbCrLf

' The default Item property throws an exception when setting
' a value if the key is of the wrong data type.
Try
   openWith(2) = "This does not get added."
Catch
   outputBlock.Text &= String.Format("A key of the wrong type was specified" _
       & " when setting the default Item property.") & vbCrLf
End Try


...


' Unlike the default Item property on the Dictionary class
' itself, IDictionary.Item does not throw an exception
' if the requested key is not in the dictionary.
outputBlock.Text &= String.Format("For key = ""tif"", value = {0}.", _
    openWith("tif")) & vbCrLf


...



   End Sub

End Class

using System;
using System.Collections;
using System.Collections.Generic;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      // Create a new dictionary of strings, with string keys,
      // and access it using the IDictionary interface.
      //
      IDictionary openWith = new Dictionary<string, string>();

      // Add some elements to the dictionary. There are no 
      // duplicate keys, but some of the values are duplicates.
      // IDictionary.Add throws an exception if incorrect types
      // are supplied for key or value.
      openWith.Add("txt", "notepad.exe");
      openWith.Add("bmp", "paint.exe");
      openWith.Add("dib", "paint.exe");
      openWith.Add("rtf", "wordpad.exe");


...


// The Item property is another name for the indexer, so you 
// can omit its name when accessing elements. 
outputBlock.Text += String.Format("For key = \"rtf\", value = {0}.",
    openWith["rtf"]) + "\n";

// The indexer can be used to change the value associated
// with a key.
openWith["rtf"] = "winword.exe";
outputBlock.Text += String.Format("For key = \"rtf\", value = {0}.",
    openWith["rtf"]) + "\n";

// If a key does not exist, setting the indexer for that key
// adds a new key/value pair.
openWith["doc"] = "winword.exe";

// The indexer returns null if the key is of the wrong data 
// type.
outputBlock.Text += String.Format("The indexer returns null"
    + " if the key is of the wrong type:") + "\n";
outputBlock.Text += String.Format("For key = 2, value = {0}.",
    openWith[2]) + "\n";

// The indexer throws an exception when setting a value
// if the key is of the wrong data type.
try
{
   openWith[2] = "This does not get added.";
}
catch (ArgumentException)
{
   outputBlock.Text += String.Format("A key of the wrong type was specified"
       + " when assigning to the indexer.") + "\n";
}


...


// Unlike the default Item property on the Dictionary class
// itself, IDictionary.Item does not throw an exception
// if the requested key is not in the dictionary.
outputBlock.Text += String.Format("For key = \"tif\", value = {0}.",
    openWith["tif"]) + "\n";


...


   }
}