bjhomer/movewindow.m

## movewindow.m
// You might think that a view could trigger window movement by overriding -[NSView mouseDownCanMoveWindow]

@interface DraggyView : NSView
@end

@implementation DraggyView
- (BOOL)mouseDownCanMoveWindow {
    return YES;
}
@end

// This probably doesn't do what you think it does, though. Specifically, it does not cause
// a mouseDragged: event to be turned into a window drag. The real API for allowing events to
// drag the window is this one:

@interface NSWindow : NSReponder
@property (getter=isMovableByWindowBackground) BOOL movableByWindowBackground;
@end

// This allows mouse events that propagate all the way up to the window (because they are
// not intercepted by some other view) to initiate a window drag. By default, opaque windows
// block mouse events from propagating up, and non-opaque views allow them to propagate.
//
// This is the behavior that is controlled by -mouseDownCanMoveWindow. If that returns YES
// (as it does by default from non-opaque views), then the mouse event will move up to the
// next view under the mouse. If NONE of the views that were under the mouse blocked it (by
// returning NO from -mouseDownCanMoveWindow), then the mouse event will reach the window
// background, and that can trigger dragging the window.
//
// However, note that this depends on every view in the view hierarchy cooperating to allow
// the event to propagate. If any view in the way handles those events for itself, then the
// event will not reach the window background, and the window drag will not be initiated.
//
// This is difficult in the Yosemite world where developers are allowed to create their own
// titlebar-like views (using NSVisualEffectMaterialTitlebar), because even though the view
// *looks* like a titlebar, it still propagates its events up the view hierarchy. There is
// no way for a view to say "I don't care what other views are under the mouse right now --
// I just want this event to initiate a window drag."
//
// Or, at least, if such an API exists, I haven't found it.
	// You might think that a view could trigger window movement by overriding -[NSView mouseDownCanMoveWindow]

	@interface DraggyView : NSView
	@end

	@implementation DraggyView
	- (BOOL)mouseDownCanMoveWindow {
	return YES;
	}
	@end

	// This probably doesn't do what you think it does, though. Specifically, it does not cause
	// a mouseDragged: event to be turned into a window drag. The real API for allowing events to
	// drag the window is this one:

	@interface NSWindow : NSReponder
	@property (getter=isMovableByWindowBackground) BOOL movableByWindowBackground;
	@end

	// This allows mouse events that propagate all the way up to the window (because they are
	// not intercepted by some other view) to initiate a window drag. By default, opaque windows
	// block mouse events from propagating up, and non-opaque views allow them to propagate.
	//
	// This is the behavior that is controlled by -mouseDownCanMoveWindow. If that returns YES
	// (as it does by default from non-opaque views), then the mouse event will move up to the
	// next view under the mouse. If NONE of the views that were under the mouse blocked it (by
	// returning NO from -mouseDownCanMoveWindow), then the mouse event will reach the window
	// background, and that can trigger dragging the window.
	//
	// However, note that this depends on every view in the view hierarchy cooperating to allow
	// the event to propagate. If any view in the way handles those events for itself, then the
	// event will not reach the window background, and the window drag will not be initiated.
	//
	// This is difficult in the Yosemite world where developers are allowed to create their own
	// titlebar-like views (using NSVisualEffectMaterialTitlebar), because even though the view
	// looks like a titlebar, it still propagates its events up the view hierarchy. There is
	// no way for a view to say "I don't care what other views are under the mouse right now --
	// I just want this event to initiate a window drag."
	//
	// Or, at least, if such an API exists, I haven't found it.