How do I help prevent my users from initiating a drag accidentally in Cocoa?

问题

I have a collection view that I've subclassed that allows me to reorder the collection view items via drag and drop. My drag code that sets up the pasterboard is currently in mouseDragged:

- (void)mouseDragged:(NSEvent *)aEvent {

    if(!dragInProgress) {
        dragInProgress = YES;

        NSPasteboard *pboard = [NSPasteboard pasteboardWithName:NSDragPboard];        

            ... setup pboard, declare types, setData ...
            ... create drag image ....

        [self  dragImage: image
                      at: position
                  offset: NSZeroSize
                   event: aEvent
              pasteboard: pboard
                  source: self
               slideBack: YES];
    }
}

I would like to only initiate a drag if the user has dragged for a certain length, so they don't initiate a drag accidentally. Is there a setting to do this in Cocoa, or do I need to move this code to mouseMoved: and check the distance between where the drag started and where the mouse is currently?

回答1:

In mouseDown:, remember where the mouse went down (locationInWindow). In mouseDragged:, subtract the location of the mouse-down event from the location of the mouse-dragged event, and compare the difference to the size returned by HIMouseTrackingGetParameters with the kMouseParamsDragInitiation selector.

来源：https://stackoverflow.com/questions/1472671/how-do-i-help-prevent-my-users-from-initiating-a-drag-accidentally-in-cocoa