[[UIBarButtonItem appearance] setTitleTextAttributes:@{NSForegroundColorAttributeName: [UIColor clearColor]} forState:UIControlStateNormal]; [[UIBarButtonItem appearance] setTitleTextAttributes:@{NSForegroundColorAttributeName: [UIColor clearColor]} forState:UIControlStateHighlighted]; 

+(void)load {  swizzleMethod([self class], @selector(viewDidAppear:), @selector(ac_viewDidAppear));}- (void)ac_viewDidAppear{  self.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc]                       initWithTitle:@""                       style:UIBarButtonItemStylePlain                       target:self                       action:nil];  [self ac_viewDidAppear];}void swizzleMethod(Class class, SEL originalSelector, SEL swizzledSelector){  // the method might not exist in the class, but in its superclass  Method originalMethod = class_getInstanceMethod(class, originalSelector);  Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);  // class_addMethod will fail if original method already exists  BOOL didAddMethod = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));  // the method doesn't exist and we just added one  if (didAddMethod) {    class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));  }  else {    method_exchangeImplementations(originalMethod, swizzledMethod);  }}