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This page contains notes about the methods you need to implement to use DragAndDrop in an NSTableView.

Please note that all information contained herein, while applicable to NSOutlineview in principle, is often implemented with its own methods. Specifically, note the NSOutlineViewDataSource protocol defines its own, equivalent drag and drop methods which function equivalently to those listed bel ow. http://goo.gl/OeSCu

Dragging to the tableview

First you need to send registerForDraggedTypes:(NSArray *)types to your tableView, with the types that you want it to be able to accept. Examples are NSStringPboardType, NSFilenamesPboardType, etc…

Apple’s Docs on this method (NSTableView inherits it from NSView, that’s where you’ll find this description):

*Registers pboardTypes as the pasteboard types that the receiver will accept as the destination of an image-dragging session.

Registering an NSView for dragged types automatically makes it a candidate destination object for a dragging session. As such, it must properly implement some or all of the NSDraggingDestination protocol methods. As a convenience, NSView provides default implementations of these methods.*

Next you need to implement some methods to accept the drag and incorporate the data. The tableview already handles the NSDraggingDestination protocol, so don’t rewrite those - you need to write these methods (in the datasource object of your tableview)

Dragging from the tableview

You need to implement this method:

You might also want to ** subclass ** NSTableView, in order to override the default behavior, which is to allow any kind of drag to within your application, and no drags to outside your application. In your subclass you need to implement the following method in the ** datasource ** object of your tablview.

This is the only required method in the NSDraggingSource informal protocol (the constants are explained in the documentation for NSDraggingInfo) Changing this method is required if you want to allow drags to other applications, because the default implementation of NSTableView returns NSDragOperationNone for isLocal = NO.

Note: the isLocal argument doesn’t tell you if the drag is coming from the same tableview! So, if you want NSDragOperationNone when it is from the same tableview but NSDragOperationCopy || NSDragOperationLink when it is from a different one, you have to return NSDragOperationNone || NSDragOperationCopy || NSDragOperationLink here if isLocal is YES, and sort it out later.

Another method you can implement in your subclass to provide a custom image is the following:

A suggestion for this one, since you know the rows, if you’re returning an NSStringPboardType in the datasource’s tableView:objectValueforTableColumn:row: method, you can save yourself the mess of duplicating code by creating a new NSPasteboard (using - pasteboardWithUniqueName ) and sending tableView:writeRows:toPasteboard: to [self dataSource], getting the string out of that Pasteboard and drawing it into the image.

If you’re not too familiar with quartz drawing, luckily this is not too bad. You just get an NSAttributedString from the NSString the pasteboard gave you, make a new NSImage (alloc, init, autorelease) and then do this dance:

[image lockFocus]; [string drawAtPoint:NSZeroPoint]; [image unlockFocus];

you can also set the dragImageOffset argument to change where the image is attached to the pointer. The caller of this method passed you an NSPointPointer, which means you should change the value of *dragImageOffset, not create a new NSPoint (on the stack) and try to pass it out by re-setting the pointer. That won’t work…

Here are Apple’s docs on this method from NSTableView.h:

</code> // This method computes and returns an image to use for dragging. Override this to return a custom image. ‘dragRows’ represents the rows participating in the drag. ‘dragEvent’ is a reference to the mouse down event that began the drag. ‘dragImageOffset’ is an in/out parameter. This method will be called with dragImageOffset set to NSZeroPoint, but it can be modified to re-position the returned image. A dragImageOffset of NSZeroPoint will cause the image to be centered under the mouse.

You might want to check out http://developer.apple.com/releasenotes/Cocoa/AppKitOlderNotes.html which has a section on Drag And Drop Support in NSTableView and NSOutlineView. I couldn’t find any other Apple documents on the subject.

Comments & Discussion: It looks like draggingSourceOperationMaskForLocal: is already implemented in the standard NSTableView, I have a running version that uses just the NSTableDataSource methods to implement rearranging the items of a table within itself.

The missing function for me to get the whole thing working was </code> registerForDraggedTypes:</code> which is a method of NSView and needs to be called on the table to enable dropping onto the table.

– HaRald

HaRald, thanks for pointing this out! I didn’t notice that. A quick look with FScript tells me that a straight NSTableView alloc, init gives me a tableview that responds to draggingSourceOperationMaskForLocal: with NSDragOperationAll for isLocal = YES, and NSDragOperationNone for isLocal = NO.

– MichaelMcCracken

Well I will give this a shot, as it has been said the documentation is there but it spans a couple of issues.

Look at MichaelMcCracken’s descriptions above for more info on the functions

NSString * const PBType = @"MyType" 

[pageTable registerForDraggedTypes:[NSArray arrayWithObject:PBType]];

Call this anywhere (awakeFromNib, windowControllerDidLoadNib, …). This actually enables you to receive Drags of the declared type(s), there are a couple of standard types declared, but using a custom type protects you from people dragging weird things into your app. A custom type acts as a filter but more specific than draggingSourceOperationMaskForLocal:.

This is part of working code, the following assumption are made and valid, this table has only one column and only one item can be selected and the items in the table are all unique strings, i did replace some variable names.

Pasteboards 101: There is a variety of boards used for different purposed (Cut and Paste, Dragging, …) each board can be supplied by one owner at a time, if someone else grabs that board the current content is invalidated. Content can be put onto the pasteboard immediately or held by the owner for lazy evaluation. It then has to be provided whenever someone else actually needs it, or application of the owner quits. The following example provides the data immediately and also only provides one type of data.

@implementation DragTableDataSource (NSTableDataSource)

}

@end

I hope you don’t mind my barging in Michael, I had this sitting around …

– HaRald

Not at all. Just one note: there are cases when [NSPasteboard pasteboardWithName:NSDragPboard] doesn’t work as expected (it isn’t guaranteed to give the right pasteboard in a drag from another application) and so you should use [info draggingPasteboard] instead.

Apple says this: “there is NO guarantee that this will be the pasteboard used in a cross-process drag. Thus, to guarantee getting the correct pasteboard, your code should use sender.draggingPasteboard() or [sender draggingPasteboard].” They say sender instead of info because they’re talking about more general NSDraggingDestination methods, not NSTableView specific methods.

Rewrote accordingly – HaRald

Stone’s (AndrewStone) Cocoamotion page at http://www.stone.com/The_Cocoa_Files/Cocoamotion.html has a bit of code they use for drag and drop reordering. It seems to work after you realize you need to add a retain/release for the row object ([array objectAtIndex:rowToMove]) to the tableView:didDepositRow:at: method.

– QetiPadgu

If you’re timid about bindings ArrayControllers, etc., and would rather do this programmatically, I would recommend the AndrewStone method that QetiPadgu pointed out. (BTW, thank you for posting it. It was a big help!)

– JasonTerhorst

So it seems no one has really gotten file dragging from an NSTableView to the Finder to work properly? I need to drag rows from my TableView to the Finder and have files created there. Promise doesn’t seem to work… anyone?

garrett

What exactly are you doing? You have to create the files, Finder can’t.

maybe this will help: check out the docs on lazy drag evaluation, basically you tell the pasteboard you have certain types of data, and if anyone wants it ask self then when it recieves you get a notification asking for the data, and in that routine you could create the files and hand back nil or something….

I just got it working. The key was to return the right constant (NSDragOperationCopy in my case) in draggingSourceOperationMaskForLocal:

Daniel

Since the introduction of bindings we don’t need a data source any more. How are drag and drop handled in NSTableView with an NSArrayController? … Nevermind, Malcolm Crawford’s bookmarks example from http://homepage.mac.com/mmalc/CocoaExamples/controllers.html shows how (and you still need a data source).

you never really needed a separate data source object - you could always have just added the NSTableDataSource protocol methods as a category on NSArray.

CAREFUL with this assumption. There are MANY circumstances where developers (such as yours truly) get caught up into trying to FORCE everything to fit into the Bindings mechanism. There is still a GREAT need for datasource/delegates. Mixing the two is perfectly normal and you shouldn’t feel like you’re doing something wrong here. ;-)

I think you mean NSArrayController…I usually end up subclassing it and designating it as a data source, a delegate, and a bindings target. It might seem like too much, but I think of it as a class that manages the table, and has array management built in. –JediKnil

Does ANYONE have an example of how to drag from an NSTableView to the desktop to create a file? I know it can be done since I’ve seen applications do it. There’s no lack of discussions on the problems people have had trying to implement this on the web, but with only bits and pieces of code that don’t provide a working example. The total lack of documentation from Apple on this is simply pathetic.

Please note that I’d like this to be compatible w/10.2 & 10.3, so I can’t use the functions provided for this (finally!) in 10.4 -Seb

I’ve struggled (as many, many others did) with this exact situation also (it is badly documented, and partially broken up to 10.3.9), and through all the noise, I did find some useful code on a mailing list (see http://cocoa.mamasam.com/COCOADEV/2003/05/1/63270.php ) which provides a ‘bare-bones’ implementation of a working tableview-to-desktop-file-creation-drag, which I will copy here for completeness:

@implementation MyTableView

�� � if (isLocal) return NSDragOperationNone; �� � else return NSDragOperationCopy; }

�� � dragPosition = [self convertPoint:[theEvent locationInWindow] fromView:nil];

�� � row = [self rowAtPoint:dragPosition];

�� � if ( (row != -1) && (row < self delegate] nRows]) ) {

�� �[self selectRow:row byExtendingSelection:NO]; �� � �� �dragPosition.x -= 16; �� �dragPosition.y -= 16; �� �imageLocation.origin = dragPosition; �� �imageLocation.size = [[NSMakeSize( 32, 32 );

�� �printf ( “mouseDown: called (x: %f, y:%f, row:%d)\n”, dragPosition.x, dragPosition.y, row );

�� �[self dragPromisedFilesOfTypes:[NSArray arrayWithObject:@””] �� � � �fromRect:imageLocation source:self slideBack:YES event:theEvent]; �� � } }

�� � return nil; }

@end

The original discussion begins at http://cocoa.mamasam.com/COCOADEV/2003/05/1/63257.php which also explains why some stuff doesn’t work as expected with drags of tableviews.

*That code sorta works, but isn’t really appropriate unless you have a static (non-selectable) table; as discussed later in that same thread, it assumes any click is a drag, and messes with the actions and makes the tableview react in a strange manner when used as a normal (selectable) tableview.

It doesn’t appear there’s any real way to accomplish this, lest Apple finally comes up with clear documentation on implementing this (contrary to others’ claims that it’s well documented)*

http://www.cocoabuilder.com/archive/message/cocoa/2003/8/20/89717 implements a slightly better version of the code above, but still inhibits double-click on rows.

File creation dragging from a [[NSTableView is definitively broken (at least on <=10.3.9). Others have tried and failed, and I’ve just joined that club. -Seb