如何在iphone的programmaticaly中添加barbutton项目

self.forwardButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemPlay
                          target:nil action:nil];

NSArray *toolBarItems = [[NSArray alloc] initWithObjects:forwardButton,nil];

[self.toolBar setItems:toolBarItems];   

[self addSubview:self.toolBar];

UIBarButtonItem *spaceItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:nil action:NULL];