Magento 2.3 Inject helper into controller object type error?

Just Remove the Generation folder or in version 2.2 remove the generated folder.

rm -rf generated/

Flush the cache. It should work then. Its because the interceptor file needs to be re-created or refresh.

You have an issue at __construct(.

You must pass the context object \Magento\Framework\App\Action\Context $context to the parent class Magento\Framework\App\Action\Action

public function __construct(
\Magento\Framework\App\Action\Context $context,
    CustomHelper $helper
) {
    $this->helper = $helper;
parent::__construct($context);
}

after these changes, when in developer mode, just remove the folders under var/generation/ or generated/ as the documentation suggests

or run setup:di:compile when in production mode

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