Cocoa Dev Central

by H. Lally Singh

NSTableView provides an easy to use interface to show and edit tabular data. All you have to do is provide a source of data, and NSTableView will do all the work, asking that source for the data it needs as it needs it.

// Providing a Data Source

To be a data source for an NSTableView, you just have to implement three methods:

• (int)numberOfRowsInTableView:(NSTableView *)aTableView - Returns the number of rows to display
• (id)tableView:(NSTableView *)aTableView objectValueForTableColumn:(NSTableColumn *)aTableColumn row:(int)rowIndex - Returns data for a given row in a given column. This data is fed into the NSCell set up for that column.
• (void)tableView:(NSTableView *)aTableView setObjectValue:(id)anObject forTableColumn:(NSTableColumn *)aTableColumn row:(int)rowIndex - Called when the user changes the value of a given data cell. Don't implement this if you want a read only NSTableView.

Using a category really makes alot of sense for many applications here. For example, if you have a single-column NSTableView, you can just use an NSArray to do all the work for you:

//
// Makes an NSArray work as an NSTableDataSource.
@implementation NSArray (NSTableDataSource)

// just returns the item for the right row
- (id)     tableView:(NSTableView *) aTableView
objectValueForTableColumn:(NSTableColumn *) aTableColumn
           row:(int) rowIndex
{  
  return [self objectAtIndex:rowIndex];  
}

// just returns the number of items we have.
- (int)numberOfRowsInTableView:(NSTableView *)aTableView
{
  return [self count];  
}
@end

It really is this easy. Just remember to call setDataSource: to tell the NSTableView who's providing the data, and call reloadData: whenever you update your data, so that NSTableView will redraw and show it!

// Customization

NSTableView is really not much more than a container for its columns, of class NSTableColumn. Each of these columns has two NSCell derivatives in it, one for the header and one for the data. Set each one using setHeaderCell: and setDataCell:.

By default, NSTableView uses an NSTextFieldCell as the cell for each column, which displays and lets the user edit text. For many applications, this is just perfect. However, you can make one column all NSButtonCells, NSImageCells or your own NSCell subclass.

Well, that's honestly about it. The documentation is pretty good on this topic, but sometimes a push start is the way to go. Enjoy Cocoa!