修改navigation bar上的 button

UIButton* modalViewButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 60, 40)];

[modalViewButton addTarget:self action:@selector(backButtonAction) forControlEvents:UIControlEventTouchUpInside];

[modalViewButton setImage:[UIImage imageNamed:@"DoneBtn.png"] forState:UIControlStateNormal];

UIBarButtonItem *modalBarButtonItem = [[UIBarButtonItem alloc] initWithCustomView:modalViewButton];

self.navigationItem.rightBarButtonItem = modalBarButtonItem;

[modalBarButtonItem release];