How to use a backend_model for my field in system.xml in Magento 2?

Question

I had setup this system.xml file

...
 <section id="account_info" translate="label" showInDefault="1" showInWebsite="1" showInStore="1">
 <label>Account configuration</label>
 <tab>account_info_tab</tab>
 <resource>myvendor_mymodule::config</resource>
 <group id="account_configuration" showInDefault="1" showInWebsite="1" showInStore="1">
 <label>Account login</label>
 <field id="title" translate="label comment" type="text" showInDefault="1" showInWebsite="1" showInStore="1">
 <label>Token API</label>
 <backend_model>Myvendor\Mymodule\Model\Config\TokenAPI</backend_model>
 <validate>required-entry</validate>
 </field>
 </group>
 </section>
...

I want to use a custom backend_model because i want to verify the data before saving it (have to use web services).

Then i have my TokenAPI backend_model

class TokenAPI extends \Magento\Framework\App\Config\Value{
 function __construct(\Magento\Framework\Exception\LocalizedException $e){
 $this->localizedException = $e;
 }
 public function beforeSave(){
 echo '<pre>';
 print_r($this->getValue());
 echo '</pre>';
 exit;
 }
} 

The problem that im having is that as soon i uncomment the backend_model in system.xml the field stops working throwing this error

[2016年05月03日 13:28:23] main.CRITICAL: Missing required argument $text of Magento\Framework\Phrase. [] []

Answer 1

The problem is that your backend model constructor does not match the parent class constructor \Magento\Framework\App\Config\Value

You need to update your constructor like this:

public function __construct(
 \Magento\Framework\Model\Context $context,
 \Magento\Framework\Registry $registry,
 \Magento\Framework\App\Config\ScopeConfigInterface $config,
 \Magento\Framework\App\Cache\TypeListInterface $cacheTypeList,
 \Magento\Framework\Model\ResourceModel\AbstractResource $resource = null,
 \Magento\Framework\Data\Collection\AbstractDb $resourceCollection = null,
 \Magento\Framework\Exception\LocalizedException $e,
 array $data = []
) {
 $this->localizedException = $e;
 parent::__construct($context, $registry, $config, $cacheTypeList, $resource, $resourceCollection, $data);
}

• Gianni Di Falco: I gives me the same error [2016年05月03日 14:36:30] main.CRITICAL: Missing required argument $text of Magento\Framework\Phrase. [] []
• Raphael at Digital Pianism: @GianniDiFalco did you flush the var folders ? Also try to add a try/catch statement around the code in the beforeSave method
• Gianni Di Falco: Do i have to delete all var/* folder? Or just my var/generation/myvendor/moydmoule?
• Raphael at Digital Pianism: @GianniDiFalco var/generation, var/cache, var/view_preprocessed
• Gianni Di Falco: Same error, the try/catch does not even execute even if a save the config with no fields showing up. The error shows in system.log and when loading the page