title: React Admin - Get current value in a form
body: <p>I am having big troubles getting the "updated" value of a record in an edit form. I always get the initial record values, even though I have an input linked to the right record source, which should update it.</p>
  
  <p>Is there an alternative way to get the values of the SimpleForm ?</p>
  
  <p>I have a simple edit form :</p>
  
  <pre><code>&lt;Edit {...props}&gt;
      &lt;SimpleForm&gt;
          &lt;MyEditForm {...props} /&gt;
      &lt;/SimpleForm&gt;
  &lt;/Edit&gt;
  </code></pre>
  
  <p>MyEditForm is as follow:</p>
  
  <pre><code>class MyEditForm extends React.Component {
      componentDidUpdate(prevProps, prevState, snapshot) {    
          console.log(prevProps.record.surface, this.props.record.surface); // &lt;-- here is my problem, both values always get the initial value I had when I fetched the resource from API
      }
  
      render() {
          return (
              &lt;div&gt;
                  &lt;TextInput source="surface" /&gt;
                  &lt;!-- other fields --&gt;
              &lt;/div&gt;
           );
      }
  }
  </code></pre>
  
  <p>I usually do it this way to get my updated component's data from other components, but in the very case of a react-admin form, I can't get it to work.</p>
  
  <p>Thanks,</p>
  
  <p>Nicolas</p>