[Mac] "Refactor" DraggableButton into a mixin and impl.

chrome/browser/ui/cocoa/draggable_button_mixin.h

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_UI_COCOA_DRAGGABLE_BUTTON_MIXIN_H_
+#define CHROME_BROWSER_UI_COCOA_DRAGGABLE_BUTTON_MIXIN_H_
+#pragma once
+
+#import <Cocoa/Cocoa.h>
+
+// The design of this class is extraordinarily poor. Apologies to all clients in
+// advance. Unfortunately, the lack of multiple inheritance and our desire to
+// avoid runtime hacks makes this convoluted dance necessary.
+//
+// Buttons that want to be draggable should implement the Mixin protocol below
+// and keep an instance of the Impl as an ivar. The button should forward mouse
+// events to the impl, which will tell the button whether or not to call super
+// and let the event be handled normally.
+//
+// If the impl decides to do work on the event, methods of the mixin protocol
+// may be called. Some of the methods declared in that protocol have base
+// implementations. If the method is not implemented by the button, that base
+// implementation will be called. Otherwise, the button's implementation will
+// be called first and the DraggableButtonResult will be used to determine
+// whether the base implementation should be called. This requires the client to
+// understand what the base does.
+
+enum DraggableButtonResult {
+  // Return values for Impl methods.
+  kDraggableButtonImplDidWork,
+  kDraggableButtonMixinCallSuper,
+
+  // Return values for Mixin methods.
+  kDraggableButtonMixinDidWork,
+  kDraggableButtonImplUseBase,
+};
+
+// Mixin Protocol //////////////////////////////////////////////////////////////
+
+// Buttons that make use of the below impl need to conform to this protocol.
+@protocol DraggableButtonMixin
+
+@required
+
+// Called when a drag should start. Implement this to do any pasteboard
+// manipulation and begin the drag, usually with
+// -dragImage:at:offset:event:. Subclasses must call one of the blocking
+// -drag* methods of NSView when implementing this method.
+- (void)beginDrag:(NSEvent*)dragEvent;
+
+@optional
+
+// Called if the actsOnMouseDown property is set. Fires the button's action and
+// tracks the click.
+- (DraggableButtonResult)performMouseDownAction:(NSEvent*)theEvent;
+
+// Implement if you want to do any extra work on mouseUp, after a mouseDown
+// action has already fired.
+- (DraggableButtonResult)secondaryMouseUpAction:(BOOL)wasInside;
+
+// Resets the draggable state of the button after dragging is finished. This is
+// called by DraggableButtonImpl when the beginDrag call returns.
+- (DraggableButtonResult)endDrag;
+
+// Decides whether to treat the click as a cue to start dragging, or to instead
+// call the mouseDown/mouseUp handler as appropriate.  Implement if you want to
+// do something tricky when making the decision.
+- (DraggableButtonResult)deltaIndicatesDragStartWithXDelta:(float)xDelta
+    yDelta:(float)yDelta
+    xHysteresis:(float)xHysteresis
+    yHysteresis:(float)yHysteresis
+    indicates:(BOOL*)result;
+
+// Decides if there is enough information to stop tracking the mouse.
+// It's deltaIndicatesDragStartWithXDelta, however, that decides whether it's a
+// drag or not. Implement if you want to do something tricky when making the
+// decision.
+- (DraggableButtonResult)deltaIndicatesConclusionReachedWithXDelta:(float)xDelta
+    yDelta:(float)yDelta
+    xHysteresis:(float)xHysteresis
+    yHysteresis:(float)yHysteresis
+    indicates:(BOOL*)result;
+
+@end
+
+// Impl Interface //////////////////////////////////////////////////////////////
+
+// Implementation of the drag and drop logic. NSButton Mixin subclasses should
+// forward their mouse events to this, which in turn will call out to the mixin
+// protocol.
+@interface DraggableButtonImpl : NSObject {
+ @private
+  // The button for which this class is implementing stuff.
+  NSButton<DraggableButtonMixin>* button_;
+
+  // Is this a draggable type of button?
+  BOOL draggable_;
+
+  // Has the action already fired for this click?
+  BOOL actionHasFired_;
+
+  // Does button action happen on mouse down when possible?
+  BOOL actsOnMouseDown_;
+
+  NSTimeInterval durationMouseWasDown_;
+  NSTimeInterval whenMouseDown_;
+}
+
+@property(nonatomic) NSTimeInterval durationMouseWasDown;
+
+@property(nonatomic) NSTimeInterval whenMouseDown;
+
+// Whether the action has already fired for this click.
+@property(nonatomic) BOOL actionHasFired;
+
+// Enable or disable dragability for special buttons like "Other Bookmarks".
+@property(nonatomic) BOOL draggable;
+
+// If it has a popup menu, for example, we want to perform the action on mouse
+// down, if possible (as long as user still gets chance to drag, if
+// appropriate).
+@property(nonatomic) BOOL actsOnMouseDown;
+
+// Designated initializer.
+- (id)initWithButton:(NSButton<DraggableButtonMixin>*)button;
+
+// NSResponder implementation. NSButton subclasses should invoke these methods
+// and only call super if the return value indicates such.
+- (DraggableButtonResult)mouseDown:(NSEvent*)event;
+- (DraggableButtonResult)mouseUp:(NSEvent*)event;
+
+@end
+
+#endif  // CHROME_BROWSER_UI_COCOA_DRAGGABLE_BUTTON_MIXIN_H_