Implementing drag and drop in NSTableView

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...
}

Solution 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

Solution 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.

Solution 3

Drag and Drop NSTableview using core data

1. 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;
}

Solution 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.

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Comments

[akhil gupta]

hi thanks for your suggestion. but i don't know how to declare a custom dragtype

[TheFuquan]

This is a more comprehensive response, thanks for your time.

[Alex]

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