为什么uibarbuttonim没有在iphone4上显示图片

- (void)viewDidLoad 
 {

   [super viewDidLoad];

   UIButton *butt = [UIButton buttonWithType:UIButtonTypeCustom];   
   [butt setImage:[UIImage imageNamed:@"reload2.png"] forState:UIControlStateNormal];
   [butt addTarget:self action:@selector(reloadNews) forControlEvents:UIControlEventTouchUpInside];
   //added the following line
   butt.frame = CGRectMake(0, 0, 30, 30);

   UIBarButtonItem *reloadButton = [[UIBarButtonItem alloc]initWithCustomView:butt];
   self.navigationItem.rightBarButtonItem = reloadButton;
   [reloadButton release];  

}