IDictionary<TKey, TValue> Interface

Type Parameters

• TKey
  The type of keys in the dictionary.

• TValue
  The type of values in the dictionary.

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 through the IDictionary generic interface.
      Dim openWith As IDictionary(Of String, String) = _
          New Dictionary(Of String, String)

      ' Add some elements to the dictionary. There are no 
      ' duplicate keys, but some of the values are duplicates.
      openWith.Add("txt", "notepad.exe")
      openWith.Add("bmp", "paint.exe")
      openWith.Add("dib", "paint.exe")
      openWith.Add("rtf", "wordpad.exe")

      ' The Add method throws an exception if the new key is 
      ' already in the dictionary.
      Try
         openWith.Add("txt", "winword.exe")
      Catch
         outputBlock.Text &= "An element with Key = ""txt"" already exists." & vbCrLf
      End Try

      ' 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 throws an exception if the requested
      ' key is not in the dictionary.
      Try
         outputBlock.Text &= String.Format("For key = ""tif"", value = {0}.", _
             openWith("tif")) & vbCrLf
      Catch
         outputBlock.Text &= "Key = ""tif"" is not found." & vbCrLf
      End Try

      ' When a program often has to try keys that turn out not to
      ' be in the dictionary, TryGetValue can be a more efficient 
      ' way to retrieve values.
      Dim value As String = ""
      If openWith.TryGetValue("tif", value) Then
         outputBlock.Text &= String.Format("For key = ""tif"", value = {0}.", value) & vbCrLf
      Else
         outputBlock.Text &= "Key = ""tif"" is not found." & vbCrLf
      End If

      ' ContainsKey can be used to test keys before inserting 
      ' them.
      If Not openWith.ContainsKey("ht") Then
         openWith.Add("ht", "hypertrm.exe")
         outputBlock.Text &= String.Format("Value added for key = ""ht"": {0}", _
             openWith("ht")) & vbCrLf
      End If

      ' When you use foreach to enumerate dictionary elements,
      ' the elements are retrieved as KeyValuePair objects.
      outputBlock.Text &= vbCrLf
      For Each kvp As KeyValuePair(Of String, String) In openWith
         outputBlock.Text &= String.Format("Key = {0}, Value = {1}", _
             kvp.Key, kvp.Value) & vbCrLf
      Next kvp

      ' To get the values alone, use the Values property.
      Dim icoll As ICollection(Of String) = openWith.Values

      ' The elements of the ValueCollection are strongly typed
      ' with the type that was specified for dictionary values.
      outputBlock.Text &= vbCrLf
      For Each s As String In icoll
         outputBlock.Text &= String.Format("Value = {0}", s) & vbCrLf
      Next s

      ' To get the keys alone, use the Keys property.
      icoll = openWith.Keys

      ' The elements of the ValueCollection are strongly typed
      ' with the type that was specified for dictionary values.
      outputBlock.Text &= vbCrLf
      For Each s As String In icoll
         outputBlock.Text &= String.Format("Key = {0}", s) & vbCrLf
      Next s

      ' Use the Remove method to remove a key/value pair.
      outputBlock.Text &= vbLf + "Remove(""doc"")" & vbCrLf
      openWith.Remove("doc")

      If Not openWith.ContainsKey("doc") Then
         outputBlock.Text &= "Key ""doc"" is not found." & vbCrLf
      End If

   End Sub

End Class

' This code example produces the following output:
'
'An element with Key = "txt" already exists.
'For key = "rtf", value = wordpad.exe.
'For key = "rtf", value = winword.exe.
'Key = "tif" is not found.
'Key = "tif" is not found.
'Value added for key = "ht": hypertrm.exe
'
'Key = txt, Value = notepad.exe
'Key = bmp, Value = paint.exe
'Key = dib, Value = paint.exe
'Key = rtf, Value = winword.exe
'Key = doc, Value = winword.exe
'Key = ht, Value = hypertrm.exe
'
'Value = notepad.exe
'Value = paint.exe
'Value = paint.exe
'Value = winword.exe
'Value = winword.exe
'Value = hypertrm.exe
'
'Key = txt
'Key = bmp
'Key = dib
'Key = rtf
'Key = doc
'Key = ht
'
'Remove("doc")
'Key "doc" is not found.
' 

using System;
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 through the IDictionary generic interface.
      IDictionary<string, string> openWith =
          new Dictionary<string, string>();

      // Add some elements to the dictionary. There are no 
      // duplicate keys, but some of the values are duplicates.
      openWith.Add("txt", "notepad.exe");
      openWith.Add("bmp", "paint.exe");
      openWith.Add("dib", "paint.exe");
      openWith.Add("rtf", "wordpad.exe");

      // The Add method throws an exception if the new key is 
      // already in the dictionary.
      try
      {
         openWith.Add("txt", "winword.exe");
      }
      catch (ArgumentException)
      {
         outputBlock.Text += "An element with Key = \"txt\" already exists." + "\n";
      }

      // 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 throws an exception if the requested key is
      // not in the dictionary.
      try
      {
         outputBlock.Text += String.Format("For key = \"tif\", value = {0}.",
             openWith["tif"]) + "\n";
      }
      catch (KeyNotFoundException)
      {
         outputBlock.Text += "Key = \"tif\" is not found." + "\n";
      }

      // When a program often has to try keys that turn out not to
      // be in the dictionary, TryGetValue can be a more efficient 
      // way to retrieve values.
      string value = "";
      if (openWith.TryGetValue("tif", out value))
      {
         outputBlock.Text += String.Format("For key = \"tif\", value = {0}.", value) + "\n";
      }
      else
      {
         outputBlock.Text += "Key = \"tif\" is not found." + "\n";
      }

      // ContainsKey can be used to test keys before inserting 
      // them.
      if (!openWith.ContainsKey("ht"))
      {
         openWith.Add("ht", "hypertrm.exe");
         outputBlock.Text += String.Format("Value added for key = \"ht\": {0}",
             openWith["ht"]) + "\n";
      }

      // When you use foreach to enumerate dictionary elements,
      // the elements are retrieved as KeyValuePair objects.
      outputBlock.Text += "\n";
      foreach (KeyValuePair<string, string> kvp in openWith)
      {
         outputBlock.Text += String.Format("Key = {0}, Value = {1}",
             kvp.Key, kvp.Value) + "\n";
      }

      // To get the values alone, use the Values property.
      ICollection<string> icoll = openWith.Values;

      // The elements of the ValueCollection are strongly typed
      // with the type that was specified for dictionary values.
      outputBlock.Text += "\n";
      foreach (string s in icoll)
      {
         outputBlock.Text += String.Format("Value = {0}", s) + "\n";
      }

      // To get the keys alone, use the Keys property.
      icoll = openWith.Keys;

      // The elements of the ValueCollection are strongly typed
      // with the type that was specified for dictionary values.
      outputBlock.Text += "\n";
      foreach (string s in icoll)
      {
         outputBlock.Text += String.Format("Key = {0}", s) + "\n";
      }

      // Use the Remove method to remove a key/value pair.
      outputBlock.Text += "\nRemove(\"doc\")" + "\n";
      openWith.Remove("doc");

      if (!openWith.ContainsKey("doc"))
      {
         outputBlock.Text += "Key \"doc\" is not found." + "\n";
      }
   }
}

/* This code example produces the following output:

An element with Key = "txt" already exists.
For key = "rtf", value = wordpad.exe.
For key = "rtf", value = winword.exe.
Key = "tif" is not found.
Key = "tif" is not found.
Value added for key = "ht": hypertrm.exe

Key = txt, Value = notepad.exe
Key = bmp, Value = paint.exe
Key = dib, Value = paint.exe
Key = rtf, Value = winword.exe
Key = doc, Value = winword.exe
Key = ht, Value = hypertrm.exe

Value = notepad.exe
Value = paint.exe
Value = paint.exe
Value = winword.exe
Value = winword.exe
Value = hypertrm.exe

Key = txt
Key = bmp
Key = dib
Key = rtf
Key = doc
Key = ht

Remove("doc")
Key "doc" is not found.
 */