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Rx Keyboard Events in WP7

/ Published in: C#
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Toying around with Rx in WP7, thought this was interesting...

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  1. // Class private var
  2. private ISubject<KeyboardState> _KeyboardStates;
  3.  
  4. // Setup in ctor
  5. _KeyboardStates = new ReplaySubject<KeyboardState>();
  6.  
  7. // In the update event
  8. _KeyboardStates.OnNext(Keyboard.GetState());
  9.  
  10. // Func to compare key states (there is probably a better solution for this)
  11. public static Func<KeyboardState, string> KeyStateComparer
  12. {
  13.     get
  14.     {
  15.         return (ks) =>
  16.         {
  17.             var sb = new StringBuilder();
  18.             ks.GetPressedKeys().ToList().ForEach((key) => sb.Append(key.ToString()));
  19.             return sb.ToString();
  20.         };
  21.     }
  22. }
  23.  
  24. // Extension method to make it easy to append this overload of distinct
  25. public static IObservable<KeyboardState> DistinctUntilChanged(this IObservable<KeyboardState> target)
  26. {
  27.     return target.DistinctUntilChanged(KeyStateComparer);
  28. }
  29.  
  30. // Now that the update event is feeding the _KeyboardStates Observable we can...
  31.  
  32. var keyPressed = from ks in _KeyboardStates.DistinctUntilChanged()
  33.                     select ks;
  34.  
  35. var keyDowns = from ks in keyPressed
  36.                     .Zip(keyPressed.Skip(1), (prev, cur) =>
  37.                     {
  38.                         return from k in cur.GetPressedKeys()
  39.                                 where !prev.GetPressedKeys().Contains(k)
  40.                                 select k;
  41.                     })
  42.                 select ks;
  43.  
  44. var keyUps = from ks in keyPressed
  45.                     .Zip(keyPressed.Skip(1), (prev, cur) =>
  46.                     {
  47.                         return from k in prev.GetPressedKeys()
  48.                                 where !cur.GetPressedKeys().Contains(k)
  49.                                 select k;
  50.                     })
  51.                 select ks;
  52.  
  53. // And with those observables we can...
  54.  
  55. keyPressed.Subscribe((keys) =>
  56. {
  57.     if (keys.GetPressedKeys().Length > 0)
  58.     {
  59.         var sb = new StringBuilder();
  60.         keys.GetPressedKeys().ToList().ForEach((key) => sb.Append(key.ToString()));
  61.         Debug.WriteLine("Keys: " + sb.ToString());
  62.     }
  63. });
  64.  
  65. keyDowns.Subscribe((keys) =>
  66.     {
  67.         foreach (var key in keys)
  68.         {
  69.             Debug.WriteLine("Key down: " + key);
  70.         }
  71.     });
  72.  
  73. keyUps.Subscribe((keys) =>
  74. {
  75.     foreach (var key in keys)
  76.     {
  77.         Debug.WriteLine("Key up: " + key);
  78.     }
  79. });

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