[objc] UINavigationBar, back btn

UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];

[button setImage:buttonImage forState:UIControlStateNormal];

button.frame = CGRectMake(0, 0, 45, 45);

[button addTarget:self action:@selector(back) forControlEvents:UIControlEventTouchUpInside];

UIBarButtonItem *customBarItem = [[UIBarButtonItem alloc] initWithCustomView:button];

self.navigationItem.leftBarButtonItem = customBarItem;