Implementing drag and drop in NSTableView - objective-c

Question

Can anyone help me to implement drag and drop in an NSTableView? I used this code below, but these methods are not getting called during execution.
- (BOOL)tableView:(NSTableView *)tv writeRowsWithIndexes:(NSIndexSet *)rowIndexes toPasteboard:(NSPasteboard*)pboard
{
// Copy the row numbers to the pasteboard.
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:rowIndexes];
[pboard declareTypes:[NSArray arrayWithObject:#".gif"] owner:self];
[pboard setData:data forType:#".gif"];
return YES;
}
- (NSDragOperation)tableView:(NSTableView*)tv validateDrop:(id <NSDraggingInfo>)info proposedRow:(NSInteger)row proposedDropOperation:(NSTableViewDropOperation)op
{
// Add code here to validate the drop
if (row > [ m_imageArray count])
return NSDragOperationNone;
if (nil == [info draggingSource]) // From other application
{
return NSDragOperationNone;
}
else if (self == [info draggingSource]) // From self
{
return NSDragOperationNone;
}
else // From other documents
{
[tv setDropRow: row dropOperation: NSTableViewDropAbove];
return NSDragOperationCopy;
}
NSLog(#"validate Drop");
return NSDragOperationCopy;
}
- (BOOL)tableView:(NSTableView *)aTableView acceptDrop:(id <NSDraggingInfo>)info
row:(NSInteger)row dropOperation:(NSTableViewDropOperation)operation
{
NSPasteboard* pboard = [info draggingPasteboard];
NSData* rowData = [pboard dataForType:#".gif"];
NSIndexSet* rowIndexes = [NSKeyedUnarchiver unarchiveObjectWithData:rowData];
NSInteger dragRow = [rowIndexes firstIndex];
// Move the specified row to its new location...
}

Answer 1

Here is an example
#import "TableViewController.h"
#import "Person.h"
#define MyDataType #"MyDataType"
#implementation TableViewController {
NSMutableArray *list;
NSInteger sourceIndex;
}
#synthesize tableView;
-(void)awakeFromNib {
[tableView registerForDraggedTypes:[NSArray arrayWithObjects:MyDataType, nil]];
list = [[NSMutableArray alloc] init];
Person *person = [[Person alloc] initWithName:#"Newton" age:64];
[list addObject:person];
person = [[Person alloc] initWithName:#"Archimedes" age:74];
[list addObject:person];
person = [[Person alloc] initWithName:#"Euler" age:44];
[list addObject:person];
person = [[Person alloc] initWithName:#"Poincare" age:24];
[list addObject:person];
person = [[Person alloc] initWithName:#"Gauss" age:34];
[list addObject:person];
}
-(void)reArrange:(NSMutableArray *)array sourceNum:(NSInteger)sourceNum destNum:(NSInteger)destNum {
Person *person = list[sourceNum];
[list insertObject:person atIndex:destNum];
if (sourceNum < destNum) {
[list removeObjectAtIndex:sourceNum];
} else {
[list removeObjectAtIndex:sourceNum+1];
}
[tableView reloadData];
}
#pragma mark - Table
// how many rows are there in the table?
-(NSInteger)numberOfRowsInTableView:(NSTableView *)tv {
return list.count;
}
// What object should I show in a particular cell?
-(id)tableView:(NSTableView *)tv objectValueForTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row {
Person *person = list[row];
NSString *identifier = [tableColumn identifier];
return [person valueForKey:identifier];
}
// Should I accept the drag with the rows specified by rowIndexes? If YES then place the data on the provided paste board.
- (BOOL)tableView:(NSTableView *)tv writeRowsWithIndexes:(NSIndexSet *)rowIndexes toPasteboard:(NSPasteboard *)pboard {
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:rowIndexes];
[pboard declareTypes:[NSArray arrayWithObject:MyDataType] owner:self];
[pboard setData:data forType:MyDataType];
sourceIndex = [rowIndexes firstIndex];
return YES;
}
// What kind of drag operation should I perform?
- (NSDragOperation)tableView:(NSTableView*)tv validateDrop:(id )info proposedRow:(NSInteger)row proposedDropOperation:(NSTableViewDropOperation)op {
return op == NSTableViewDropAbove; // Specifies that the drop should occur above the specified row.
}
// The mouse button was released over a row in the table view, should I accept the drop?
- (BOOL)tableView:(NSTableView*)tv acceptDrop:(id )info row:(NSInteger)row dropOperation:(NSTableViewDropOperation)op {
[self reArrange:list sourceNum:sourceIndex destNum:row]; // let the source array reflect the change
return YES;
}
#end

Answer 2

You need to declare a custom drag type for your table view and then call registerForDraggedTypes: with your custom type. Otherwise, as you have noticed, none of these methods will get called.

Answer 3

Drag and Drop NSTableview using core data
Register table-view object for drag and drop:-
[tblCategory registerForDraggedTypes:[NSArray arrayWithObject:#"public.text"]];
Drag and drop Delegate methods:-
- (id <NSPasteboardWriting>)tableView:(NSTableView *)tableView pasteboardWriterForRow:(NSInteger)row
{
Category *category = (Category *)[self.arrCategoryList objectAtIndex:row];
NSString *identifier = category.categoryname;
NSPasteboardItem *pboardItem = [[NSPasteboardItem alloc] init];
[pboardItem setString:identifier forType: #"public.text"];
return pboardItem;
}
- (NSDragOperation)tableView:(NSTableView *)tableView validateDrop:(id <NSDraggingInfo>)info proposedRow:(NSInteger)row proposedDropOperation:(NSTableViewDropOperation)dropOperation
{
if(dropOperation == NSTableViewDropOn)
{
NSPasteboard *p = [info draggingPasteboard];
NSString *title = [p stringForType:#"public.text"];
Category* category ;
NSInteger srcIndex;
for (srcIndex = 0; srcIndex < [_arrCategoryList count]; srcIndex++)
{
category = [_arrCategoryList objectAtIndex:srcIndex];
if ([category.categoryname isEqualToString:title])
{
break;
}
category = nil;
}
if(!category)
{
// Not found
return NO;
}
[_arrCategoryList removeObjectAtIndex:srcIndex];
[_arrCategoryList insertObject:category atIndex:row];
[tblCategory reloadData];
return NSDragOperationMove;
}
return NSDragOperationNone;
}
- (BOOL)tableView:(NSTableView *)tableView acceptDrop:(id <NSDraggingInfo>)info row:(NSInteger)row dropOperation:(NSTableViewDropOperation)dropOperation
{
return YES;
}

Answer 4

I usually observe this kind of error when I forgot to hook up the dataSource to the NSTabeView in IB, i.e. the class implementing the tableView:writeRowsWithIndexes:toPasteboard: method of the NSTableViewDataSource.

Answer 5

You can register for draggedTypes for an NSMutableArray or NSMutableDictionary or any other object.Following Code snippet is for a NSMutableArray.
[tableView registerForDraggedTypes:[NSArray arrayWithObject:#"NSMutableArray"] ];

Answer 6

You need to declare a registerForDraggedTypes method in awakFromnib
like this.
[table_view registerForDraggedTypes:[NSArray arrayWithObjects:BasicTableViewDragAndDropDataType, nil]];

Answer 7

I have to recommend both this excellent Red Sweater blog post
http://www.red-sweater.com/blog/274/a-moveable-beast
It provides an NSArrayController sub-class which will enable drag and drop re-ordering of table items, and if you want to support dragging outside of the tableview with your objects, we've just written up a neat and simple addition to that class:
http://www.rwe-uk.com/blog/comments/nstableview_drag_and_drop_with_bindings_and_nsarraycontroller
It builds on the original post