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      1 // Copyright (c) 2012 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_WM_WINDOW_CYCLE_CONTROLLER_H_
      6 #define ASH_WM_WINDOW_CYCLE_CONTROLLER_H_
      7 
      8 #include "ash/ash_export.h"
      9 #include "base/basictypes.h"
     10 #include "base/memory/scoped_ptr.h"
     11 
     12 namespace ui {
     13 class EventHandler;
     14 }
     15 
     16 namespace ash {
     17 
     18 class WindowCycleList;
     19 
     20 // Controls cycling through windows with the keyboard, for example, via alt-tab.
     21 // Windows are sorted primarily by most recently used, and then by screen order.
     22 // We activate windows as you cycle through them, so the order on the screen
     23 // may change during the gesture, but the most recently used list isn't updated
     24 // until the cycling ends.  Thus we maintain the state of the windows
     25 // at the beginning of the gesture so you can cycle through in a consistent
     26 // order.
     27 class ASH_EXPORT WindowCycleController {
     28  public:
     29   enum Direction {
     30     FORWARD,
     31     BACKWARD
     32   };
     33   WindowCycleController();
     34   virtual ~WindowCycleController();
     35 
     36   // Returns true if cycling through windows is enabled. This is false at
     37   // certain times, such as when the lock screen is visible.
     38   static bool CanCycle();
     39 
     40   // Cycles between windows in the given |direction|. If |is_alt_down| then
     41   // interprets this call as the start of a multi-step cycle sequence and
     42   // installs a key filter to watch for alt being released.
     43   void HandleCycleWindow(Direction direction, bool is_alt_down);
     44 
     45   // Cycles between windows without maintaining a multi-step cycle sequence
     46   // (see above).
     47   void HandleLinearCycleWindow();
     48 
     49   // Informs the controller that the Alt key has been released and it can
     50   // terminate the existing multi-step cycle.
     51   void AltKeyReleased();
     52 
     53   // Returns true if we are in the middle of a window cycling gesture.
     54   bool IsCycling() const { return windows_.get() != NULL; }
     55 
     56   // Returns the WindowCycleList. Really only useful for testing.
     57   const WindowCycleList* windows() const { return windows_.get(); }
     58 
     59  private:
     60   // Call to start cycling windows.  You must call StopCycling() when done.
     61   void StartCycling();
     62 
     63   // Cycles to the next or previous window based on |direction|.
     64   void Step(Direction direction);
     65 
     66   // Installs an event filter to watch for release of the alt key.
     67   void InstallEventFilter();
     68 
     69   // Stops the current window cycle and cleans up the event filter.
     70   void StopCycling();
     71 
     72   scoped_ptr<WindowCycleList> windows_;
     73 
     74   // Event handler to watch for release of alt key.
     75   scoped_ptr<ui::EventHandler> event_handler_;
     76 
     77   DISALLOW_COPY_AND_ASSIGN(WindowCycleController);
     78 };
     79 
     80 }  // namespace ash
     81 
     82 #endif  // ASH_WM_WINDOW_CYCLE_CONTROLLER_H_
     83