AFViewShaker * viewShaker = [[AFViewShaker alloc] initWithView:self.formView];

NSArray * allFields = @[self.emailField, self.passwordField];
AFViewShaker * viewShaker = [[AFViewShaker alloc] initWithViewsArray:allFields];

[self.viewShaker shake];

[self.viewShaker shakeWithDuration:0.6 completion:^{
    NSLog(@"Hello World!");
}];