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Re: Preventing a drag in draggingSourceOperationMaskForLocal: not working
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Re: Preventing a drag in draggingSourceOperationMaskForLocal: not working


  • Subject: Re: Preventing a drag in draggingSourceOperationMaskForLocal: not working
  • From: "Jeremy Higgs" <email@hidden>
  • Date: Sun, 24 Sep 2006 16:34:38 +1000

On 9/23/06, Corbin Dunn <email@hidden> wrote:

> > I'm trying to implement horizontal dragging in an NSTableView cell > (the same > sort of functionality iTunes provides when setting song ratings), > but am > having some problems. I have overridden the > draggingSourceOperationMaskForLocal: method in an NSTableView subclass > (which has been set as the custom class in the nib) to do the > following: > > - (NSDragOperation)draggingSourceOperationMaskForLocal:(BOOL)isLocal; > { > // If we're in one of the "no-drag" columns (set in mouseDown:) > don't > allow a drag to occur > if (!_horizontalMotionCanBeginDrag) > { > return NSDragOperationNone; > } > > return [super draggingSourceOperationMaskForLocal:isLocal]; > } > > The value for _horizontalMotionCanBeginDrag is set in mouseDown:, by > checking if the mouse cursor is in one of the table columns we want to > disable drags in: > > - (void)mouseDown:(NSEvent *)event > { > BOOL mouseInNoDragColumns = ([[[self > mouseTableColumnForEvent:event] > identifier] isEqualToString:@"columnA"] || > [[[self > mouseTableColumnForEvent:event] > identifier] isEqualToString:@"columnB"]); > > // If we're in a "no-drag" column, flag it > _horizontalMotionCanBeginDrag = !mouseInNoDragColumns; > > [super mouseDown:event]; > } > > --- > > When I try and perform a "horizontal" drag in those particular > cells, I can > see NSDragOperationNone being returned from the > draggingSourceOperationMaskForLocal: method. Despite this, a drag > image is > still produced (and a drag occurs, as writeRows: in the delegate is > called). > According to the docs, this is what I should be doing to prevent a > drag from > this row.

That's too late to do it. From a table, do this in your delegate:

- (BOOL)tableView:(NSYourTableView *)tableView writeRowsWithIndexes:
(NSIndexSet *)rowIndexes toPasteboard:(NSPasteboard*)pboard {
    if ([tableView canDrag])  { ... stuff } else { return NO; }
}

set the "canDrag" in the subclass of your tableview (NSYourTableView)
with mouseDown: code similar to what you have.

I understand this is difficult to do and something like this will be
made easier to do in the future.

thanks,
--corbin


Hi Corbin,

Thanks a lot for that! Works a treat now.

Jeremy
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References: 
 >Preventing a drag in draggingSourceOperationMaskForLocal: not working (From: "Jeremy Higgs" <email@hidden>)
 >Re: Preventing a drag in draggingSourceOperationMaskForLocal: not working (From: Corbin Dunn <email@hidden>)

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