C# 中的Map: Dictionary 的使用

We can use the statement, DicObj[keyObj] = valObject, to set/get the value corresponding to the key.

using System;
using System.Collections.Generic;

public class Example
{
public static void Main()
{
  // Create a new dictionary of strings, with string keys.
  //
  Dictionary<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)
  {
      Console.WriteLine("An element with Key = \"txt\" already exists.");
  }

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

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

  // 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
  {
      Console.WriteLine("For key = \"tif\", value = {0}.",
          openWith["tif"]);
  }
  catch (KeyNotFoundException)
  {
      Console.WriteLine("Key = \"tif\" is not found.");
  }

  // 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))
  {
      Console.WriteLine("For key = \"tif\", value = {0}.", value);
  }
  else
  {
      Console.WriteLine("Key = \"tif\" is not found.");
  }

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

  // When you use foreach to enumerate dictionary elements,
  // the elements are retrieved as KeyValuePair objects.
  Console.WriteLine();
  foreach( KeyValuePair<string, string> kvp in openWith )
  {
      Console.WriteLine("Key = {0}, Value = {1}",
          kvp.Key, kvp.Value);
  }

  // To get the values alone, use the Values property.
  Dictionary<string, string>.ValueCollection valueColl =
      openWith.Values;

  // The elements of the ValueCollection are strongly typed
  // with the type that was specified for dictionary values.
  Console.WriteLine();
  foreach( string s in valueColl )
  {
      Console.WriteLine("Value = {0}", s);
  }

  // To get the keys alone, use the Keys property.
  Dictionary<string, string>.KeyCollection keyColl =
      openWith.Keys;

  // The elements of the KeyCollection are strongly typed
  // with the type that was specified for dictionary keys.
  Console.WriteLine();
  foreach( string s in keyColl )
  {
      Console.WriteLine("Key = {0}", s);
  }

  // Use the Remove method to remove a key/value pair.
  Console.WriteLine("\nRemove(\"doc\")");
  openWith.Remove("doc");

  if (!openWith.ContainsKey("doc"))
  {
      Console.WriteLine("Key \"doc\" is not found.");
  }
}
}

/* 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.
*/