単に initWithImage を割り当てる代わりに: アプリのすべての UIBarButtonItems に同じ画像を追加したい場合は、appdelegae.m でこのメソッドを使用できます。
- (void)customizeAppearance
{
// Customize the UIBarButtonItem
// Create resizable images
UIImage *button30 = [[UIImage imageNamed:@"button_textured_30"]
resizableImageWithCapInsets:UIEdgeInsetsMake(0, 5, 0, 5)];
UIImage *button24 = [[UIImage imageNamed:@"button_textured_24"]
resizableImageWithCapInsets:UIEdgeInsetsMake(0, 5, 0, 5)];
[[UIBarButtonItem appearance] setBackgroundImage:button30 forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];
[[UIBarButtonItem appearance] setBackgroundImage:button24 forState:UIControlStateNormal barMetrics:UIBarMetricsLandscapePhone];
}