ash/accelerators/key_hold_detector.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef ASH_ACCELERATOR_KEY_HOLD_DETECTOR_H_
   6 #define ASH_ACCELERATOR_KEY_HOLD_DETECTOR_H_
   7
   8 #include "ash/ash_export.h"
   9 #include "base/memory/scoped_ptr.h"
  10 #include "ui/events/event_handler.h"
  11
  12 namespace ui {
  13 class KeyEvent;
  14 }
  15
  16 namespace ash {
  17
  18 // This class is used to implement action when a user press and hold the key.
  19 // When a user just pressed and released a key, normal pressed event gets
  20 // generated upon release.
  21 class ASH_EXPORT KeyHoldDetector : public ui::EventHandler {
  22  public:
  23   class Delegate {
  24    public:
  25     virtual ~Delegate() {}
  26
  27     // If this return false, the event handler does not process
  28     // the event at all.
  29     virtual bool ShouldProcessEvent(const ui::KeyEvent* event) const = 0;
  30
  31     // This should return true if the event should start the state transition.
  32     virtual bool IsStartEvent(const ui::KeyEvent* event) const = 0;
  33
  34     // Whether to stop event propagation after processing.
  35     virtual bool ShouldStopEventPropagation() const = 0;
  36
  37     // Called when the key is held.
  38     virtual void OnKeyHold(const ui::KeyEvent* event) = 0;
  39
  40     // Called when the key is release after hold.
  41     virtual void OnKeyUnhold(const ui::KeyEvent* event) = 0;
  42   };
  43
  44   explicit KeyHoldDetector(scoped_ptr<Delegate> delegate);
  45   ~KeyHoldDetector() override;
  46
  47   // ui::EventHandler overrides:
  48   void OnKeyEvent(ui::KeyEvent* key_event) override;
  49
  50  private:
  51   // A state to keep track of one click and click and hold operation.
  52   //
  53   // One click:
  54   // INITIAL --(first press)--> PRESSED --(release)--> INITIAL[SEND PRESS]
  55   //
  56   // Click and hold:
  57   // INITIAL --(first press)--> PRESSED --(press)-->
  58   //   HOLD[OnKeyHold] --(press)--> HOLD[OnKeyHold] --(release)-->
  59   //   INITIAL[OnKeyUnhold]
  60   enum State {
  61     INITIAL,
  62     PRESSED,
  63     HOLD
  64   };
  65
  66   State state_;
  67   scoped_ptr<Delegate> delegate_;
  68
  69   DISALLOW_COPY_AND_ASSIGN(KeyHoldDetector);
  70 };
  71
  72 }  // namespace ash
  73
  74 #endif  // ASH_ACCELERATOR_KEY_HOLD_DETECTOR_H_