Typo3 Extension Flexform onchange reload

You want your typo flexform to reload after the backend user selects something.

Add the reload before your config Tag:

<T3DataStructure>
  <sheets>
    <sDEF>
      <ROOT>
        <TCEforms>
          <sheetTitle>LLL:EXT:extension/res/lang/flexform.xml:sheet_general</sheetTitle>
        </TCEforms>
        <type>array</type>
        <el>
          <topCategory>
            <TCEforms>
              <label>LLL:EXT:extension/res/lang/flexform.xml:topCategory</label>
              <onChange>reload</onChange>
              <config>
                <type>group</type>
                <internal_type>db</internal_type>
                <allowed>pages</allowed>
                <size>1</size>
                <minitems>1</minitems>
                <maxitems>1</maxitems>
              </config>
            </TCEforms>
          </topCategory>
        </el>
      </ROOT>
    </sDEF>
  </sheets>
</T3DataStructure>