Double click an NSTableView row in Cocoa?

Take a look at the -setDoubleAction: method on NSTableView; you can set that to a method that will be called just like the normal target-action system but on a double-click.

In that action method, -clickedRow will be useful.

Adding more basic information to @JimPuls answer for the benefit of other newcomers to Cocoa.

1. An IBOutlet to the NSTableView needs to be declared in an interface. I assumed it is preferred to do so in the table's delegate.
2. The IBOutlet to the table needs to be connected via Interface Builder. To do that Ctrl-Drag & Drop in IB from the class that declares the outlet to the table view. When you release your mouse a popup should appear with the name of the outlet you declared in step #1. Select that.
3. In the @implementation section, on the -awakeFromNib method, call -setTarget: and -setDoubleAction: on the IBOutlet declared in step #1 and connected in step #2.

Here's an excerpt from my table view delegate. I have my delegate also set up as the datasource, so that's why you'll see both the NSTableViewDelegate and NSTabeViewDataSource interfaces associated with it.

// Interface excerpt.

@interface MyTableViewDelegate : NSObject <NSTableViewDelegate, NSTableViewDataSource>
{
  // This iVar needs to be connected to the table view via the IB.
  IBOutlet NSTableView *tableOutlet;
}

@property (assign) IBOutlet NSTableView *tableOutlet;

- (void)doubleClick:(id)nid;

@end

// Implementation excerpt.

@implementation MyTableViewDelegate

@synthesize tableOutlet = _tableOutlet;

- (void)awakeFromNib {
  [_tableOutlet setTarget:self];
  [_tableOutlet setDoubleAction:@selector(doubleClick:)];
}

- (void)doubleClick:(id)object {
  // This gets called after following steps 1-3.
  NSInteger rowNumber = [_tableOutlet clickedRow];
  // Do something...
}

Hope this helps.