How to not resign first responder for UITextField in iOS

Issue #353

When using STPPaymentCardTextField from stripe-ios, the default behavior is when we touch outside to dismiss keyboard, it checks and focus on number text field is it is invalid

STPPaymentCardTextField.m

- (STPFormTextField *)currentFirstResponderField {
    for (STPFormTextField *textField in [self allFields]) {
        if ([textField isFirstResponder]) {
            return textField;
        }
    }
    return nil;
}

- (BOOL)canResignFirstResponder {
    return [self.currentFirstResponderField canResignFirstResponder];
}

- (BOOL)resignFirstResponder {
    [super resignFirstResponder];
    BOOL success = [self.currentFirstResponderField resignFirstResponder];
    [self layoutViewsToFocusField:nil
                         animated:YES
                       completion:nil];
    [self updateImageForFieldType:STPCardFieldTypeNumber];
    return success;
}

Then it calls [self.numberField becomeFirstResponder]; is validation on number fails

typedef void (^STPLayoutAnimationCompletionBlock)(BOOL completed);
- (void)layoutViewsToFocusField:(NSNumber *)focusedField
                       animated:(BOOL)animated
                     completion:(STPLayoutAnimationCompletionBlock)completion {

    NSNumber *fieldtoFocus = focusedField;

    if (fieldtoFocus == nil
        && ![self.focusedTextFieldForLayout isEqualToNumber:@(STPCardFieldTypeNumber)]
        && ([self.viewModel validationStateForField:STPCardFieldTypeNumber] != STPCardValidationStateValid)) {
        fieldtoFocus = @(STPCardFieldTypeNumber);
        [self.numberField becomeFirstResponder];
    }
}

isUserInteractionEnabled

Be aware to use isUserInteractionEnabled on STPPaymentCardTextField as that can resign first responder when set to true and become first responder when set to false