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eyadams · Jan 3, 2001, 09:33 AM

I've been trying to implement drag and drop support in a NSTableView, and I'm having problems.

What I'd like to do is allow my users re-order rows in the table via drag and drop. I've implemented tableViewWriteRowsToPasteboard(), tableViewValidateDrop(), tableViewAcceptDrop(), and tableViewSetObjectValueForLocation(). But only tableViewWriteRowsToPasteboard() is being called - the other methods never are. I suspect there's a problem with my code, and that for some reason the data isn't being put into the pasteboard. I've put the source at the end of this message.

If anyone can point me to a sample application that uses drag and drop within an NSTableView (either Obj C or Java) I would appreciate it.

public Object tableViewObjectValueForLocation(NSTableView tab,
NSTableColumn col, int i) {

if (col.identifier().toString().equals("COL1"))
return ((row)rowData.elementAt(i)).newsgroup;
else if (col.identifier().toString().equalsIgnoreCase("COL 2"))
return ((row)rowData.elementAt(i)).unread;
else
return ("unknown col id: " + col.identifier().toString());

}

Any help is appreciated.

Erik

RichardS · Jan 3, 2001, 12:07 PM

Ahhh, I recently tackled this with my OS X NotePad app (Notes, check on versiontracker).

Since I am fairly new to Cocoa, it didn't take me long to realize that implementing Drag&Drop in a NSTableView was far beyond me.

So, when you can't write it yourself... shamelessly rip off someone else's code!

Andrew Stone put up the source code to GIFfun, which contains a NSTableView with Drag&Drop row re-ordering. I just moved his SDTableView class into my application, as well as the formal protocol declaration (both without modification, it's very well written!), added the delegate methods to my controller class, and it was working!

Took me about half an hour, tops. His class also lets you set a key modifier that must be pressed down for the drag to start. I used this in Notes, because if the user moved the mouse at all while clicking (very likely) then it would start to drag, and then snap back when the mouse was released, and this caused wierd behavior.

I also don't know if you are allowed to create commerical software with Stone's code. Notes is freeware, so I was not really too concerned about that. If you want, I can send you the Notes source, to see how it's implemented. You should be able to just copy out the files that I used, and add (I think) 3 very simple delegate methods to the SDTableView delegate, and it'll start working.

Very cool indeed.

Also, I highly suggest you pick up the latest issue of MacTech magazine. It contains an article written by Andrew Stone which runs through a basic drag & drop implementation. (This guy is everywhere, and that's a good thing!). This issue of MacTech came out after I released Notes, so I did this on the GIFfun source alone (meaning you don't need the MacTech to do this, it will just explain how the Drag & Drop works).

Good Luck!

macrophyllum · May 3, 2002, 06:53 PM

Does anyone have sample code for how to do this in Cocoa Java?

Ghoser777 · May 3, 2002, 08:48 PM

This honestly doesn't look that hard. You just need to implement three methods in your delegate, something like this (because someone suggested the java example, we'll go with that)

<BLOCKQUOTE>code:<HR><pre>
String myType = "myType";

public boolean tableViewWriteRowsToPasteboard( NSTableView tableView, NSArray rows, NSPasteboard pboard)
{
pboard.declareTypes(new NSArray(myType))
//myData is up to you how you define it
pboard.setDataForType(myData,myType);
return true;
}

public int tableViewValidateDrop( NSTableView tableView, NSDraggingInfo info, int row, int operation)
{
if(operation==NSDraggingInfo.DragOperationMove) return operation;
else return DragOperationNone;
}

public boolean tableViewAcceptDrop( NSTableView tableView, NSDraggingInfo info, int row, int operation)
{
//this is the data that I told you to encode earlier!
NSData myDaya = info.draggingPasteboard().dataForType(myType);
//now insert this data into the appropriate positions
}
[/code]

Now, I didn't check this code yet (finals... must study...), but something like this should world.

HTH,
F-bacher

Ghoser777 · May 3, 2002, 08:50 PM

Originally posted by eyadams:
If anyone can point me to a sample application that uses drag and drop within an NSTableView (either Obj C or Java) I would appreciate it.

I believe there's an example with drag and drop with an outline view in the AppKit examples that come with the dev tools. OutlineView is just a subclass of NSTableView, so there should be some similarities.

F-bacher

macrophyllum · May 5, 2002, 12:42 PM

F-Bacher thanks for the help, I am a beginner so please bear with me. Below is the code that I got (after looking at your example code). The tableViewAcceptDrop and tableViewValidateDrop are NOT getting called. The tableViewWriteRowsToPasteboard is getting called. If you can take a look at it and let me know what you think that would be greatly appreciated. Thanks,
Ian

public boolean tableViewWriteRowsToPasteboard(NSTableView aTable, NSArray anArray, NSPasteboard aPastboard ) {
//When I click and drag a row in the table, the strings from that row move around with the mouse arrow.
NSArray newArray = new NSArray();
newArray = newArray.arrayByAddingObject(NSPasteboard.DragPboa rd);

dataString = new String();
String[][] defaultMatrix;
defaultMatrix = getMatrix(); //returns a String[][] that holds the strings that are displayed in the table
for (int i=0; i<numberOfRows; i++) {
for (int j=0; j<numberOfColumns; j++) {
String f = defaultMatrix[i][j];
dataString = dataString + f; //put all of the strings together
}
}

aPastboard.declareTypes(newArray,null);
aPastboard.setStringForType(dataString, NSPasteboard.DragPboard);
return true;
}
public boolean tableViewAcceptDrop(NSTableView tableView, NSDraggingInfo info, int row, int operation) {
//don't know why this method doesn't get called
String data = info.draggingPasteboard().stringForType(dataString );
//not sure how to make it insert it where appropriate
return true;

}

public int tableViewValidateDrop(NSTableView tableView, NSDraggingInfo info, int row, int operation) {

if(operation==NSDraggingInfo.DragOperationMove) return operation;
else return NSDraggingInfo.DragOperationNone;

}

[ 05-05-2002: Message edited by: macrophyllum ]

lindberg · May 8, 2002, 03:03 PM

I think you need to call registerForDraggedTypes() on the NSTableView so it knows to accept your type.

Also, NSPasteboard.DragPboard is the string name of a pasteboard, not a pastboard type. You normally use those to get an NSPasteboard instance (the pasteboardWithName() method), but in this case it's passed to you already. The constants ending in "PboardType" are the ones normally used. Any string is OK, and since this is a custom operation (i.e. nothing is being dragged to other applications) you probably want to use a custom string (can be anything, really). In this sense, NSPasteboard.DragPboard probably would work as a random string, but it's confusing to see in the code.

macrophyllum · May 9, 2002, 02:13 AM

lindberg,

Thanks for replying. I will implement the method you suggested when I get a chance (I just upgraded). I can't even look at the documentation now (download in progress) to see what to put in that method. I am sure I will be posting again in this thread.

Thanks,
Ian

geowerker · Jun 12, 2002, 05:52 PM

I don't know if you got this working or not, but I was struggling with it last night and made it work in java. Things to note:

--------------------
In tableViewWriteRowsToPasteboard(), you need to call:
<blockquote>code:<hr /><pre style="font-size:x-small; font-family: monospace;">
pboard.declareTypes(new NSArray("DragData&quot

,null);</pre><hr /></blockquote>and either:
<blockquote>code:<hr /><pre style="font-size:x-small; font-family: monospace;">pboard.setStringForType(someString,&am p;quot;DragData&quot

;</pre><hr /></blockquote>or:
<blockquote>code:<hr /><pre style="font-size:x-small; font-family: monospace;">pboard.setDataForType(someData,&qu ot;DragData&quot

;</pre><hr /></blockquote>Assuming your just moving rows within one table, it's not necessary to drag all the data from the selected rows. Just put a comma delimeted string of the row numbers on the pasteboard and then parse it to see which rows to copy, insert, and then delete as they get added at the new drop location.

---------------
Lindberg wrote:
<blockquote>quote:<hr /> I think you need to call registerForDraggedTypes() on the NSTableView so it knows to accept your type. <hr /></blockquote>YES YES YES - I have a TableViewController class (set as the delegate for the NSTableView in my nib file) which contains:
<blockquote>code:<hr /><pre style="font-size:x-small; font-family: monospace;">public void awakeFromNib() {
myTableView.registerForDraggedTypes(new NSArray("DragData&quot

);
}</pre><hr /></blockquote>Once this was in I started getting suggestions for drop locations in the table.

-------------
In 'tableViewValidateDrop', the 'int operation' values are 1=betweenrows and 0=overrow. I just wanted to be able to drop between rows so:
<blockquote>code:<hr /><pre style="font-size:x-small; font-family: monospace;">public int tableViewValidateDrop (NSTableView tV, NSDraggingInfo info, int row, int operation) {
if (operation == 1) {
return NSDraggingInfo.DragOperationMove;
} else {
return NSDraggingInfo.DragOperationNone;
}
}</pre><hr /></blockquote>Hope this helps
GW