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private void btnGet_Click(object sender, EventArgs e) 
{ 
  //Obtain a reference to the default MemoryCache instance. 
  //Note that you can create multiple MemoryCache(s) inside 
  //of a single application. 
  ObjectCache cache = MemoryCache.Default; 
  
  //In this example the cache is storing the contents of a file string 
  fileContents = cache["filecontents"] as string;
  
  //If the file contents are not currently in the cache, then 
  //the contents are read from disk and placed in the cache. 
  if (fileContents == null) 
  {
    //A CacheItemPolicy object holds all the pieces of cache 
    //dependency and cache expiration metadata related to a single 
    //cache entry. 
    CacheItemPolicy policy = new CacheItemPolicy(); 
    
    //Build up the information necessary to create a file dependency. 
    //In this case we just need the file path of the file on disk. 
    List filePaths = new List(); 
    filePaths.Add("c:\\data.txt"); 
    
    //In the new cache API, dependencies are called "change monitors". 
    //For this example we want the cache entry to be automatically expired 
    //if the contents on disk change. A HostFileChangeMonitor provides 
    //this functionality. 
    policy.ChangeMonitors.Add(new HostFileChangeMonitor(filePaths)); 
    
    //Fetch the file's contents 
    fileContents = File.ReadAllText("c:\\data.txt"); 
    
    //And then store the file's contents in the cache 
    cache.Set("filecontents", fileContents, policy); 
    
  } 
  MessageBox.Show(fileContents); 
}