title: Get URL parameters inside custom module
body: <p>I've created a custom block like this:</p>
  
  <pre><code>class HelloBlock extends BlockBase implements BlockPluginInterface{
  
    /**
     * {@inheritdoc}
     */
    public function build() {
      $config = $this-&gt;getConfiguration();
      $result = db_query('SELECT * FROM {test}');
      return array(
        '#theme' =&gt; 'world',
        '#test' =&gt; $result
      );
    }
  }
  </code></pre>
  
  <p>And I now want to programmatically get some parameter from the URL.</p>
  
  <p>For example:</p>
  
  <p>If the URL is <code>http://localhost/drup/hello/5569</code> I want to get hold of the value <code>5569</code> inside my module. </p>
  
  <p>I have tried <code>arg(1)</code> and <code>drupal_get_query_parameters()</code> but I got this error messages:</p>
  
  <pre><code>Call to undefined function `Drupal\hello\Plugin\Block\arg()`
  </code></pre>
  
  <p>and</p>
  
  <pre><code>Call to undefined function `Drupal\hello\Plugin\Block\drupal_get_query_parameters()`
  </code></pre>
  
  <p>How can I get the parameters?</p>