iOS 修改AlertViewController弹框的字体颜色及字体的方法

系统默认的字体是黑色，按钮颜色是蓝色或者红色的，自定义字体如下

UIAlertController *alertVC = [UIAlertController alertControllerWithTitle:@"提示" message:@"确认退出登录？" preferredStyle:(UIAlertControllerStyleAlert)];
 UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {
 NSLog(@"点击了Cancel");
 [alertVC dismissViewControllerAnimated:YES completion:nil];
 }];
 UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
 NSLog(@"点击了OK");
 [[NSUserDefaults standardUserDefaults] setObject:nil forKey:kLoginUserKey];
 [alertVC dismissViewControllerAnimated:YES completion:nil];
 }];
 //修改title
 NSMutableAttributedString *alertControllerStr = [[NSMutableAttributedString alloc] initWithString:@"提示"];
 [alertControllerStr addAttribute:NSForegroundColorAttributeName value:kMainTextColor range:NSMakeRange(0, 2)];
 [alertControllerStr addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:15] range:NSMakeRange(0, 2)];
 [alertVC setValue:alertControllerStr forKey:@"attributedTitle"];
 //修改message
 NSMutableAttributedString *alertControllerMessageStr = [[NSMutableAttributedString alloc] initWithString:@"确认退出登录？"];
 [alertControllerMessageStr addAttribute:NSForegroundColorAttributeName value:kSubTextColor range:NSRangeFromString(@"确认退出登录？")];
 [alertControllerMessageStr addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:13] range:NSRangeFromString(@"确认退出登录？")];
 [alertVC setValue:alertControllerMessageStr forKey:@"attributedMessage"];
 //修改按钮字体颜色
 [cancelAction setValue:kGreenColor forKey:@"titleTextColor"];
 [okAction setValue:kGreenColor forKey:@"titleTextColor"];