title: In a List of flutter multiselect, on selecting an item in one multiselect, all other multiselects with same item should get selected
body: <p>I have multiple multi-select dropdowns with repeated options through the dropdowns.
  Example Dropdown1 - Options [A,B,C,D]
  Dropdown2 - Options [D,E,F,G]
  So I want when I select Options A,D in the first dropdown, the option D of the second dropdown also gets selected at the same time.</p>
  <p>The problem is FlutterMultiChipSelect (package: flutter_multi_chip_select) widget does not provide any event like on_selection/on_change where I can write the code to change selection for other multiselect dropdowns. It is managing the selection change internally.</p>
  <pre><code>final menuItems = [&quot;A&quot;,&quot;B&quot;,&quot;C&quot;,&quot;D&quot;];
  var selectedItems = [];
  
  FlutterMultiChipSelect(
              key: key,
              elements: List.generate(
                menuItems.length,
                    (index) =&gt; MultiSelectItem&lt;String&gt;.simple(
                    title: menuItems[index].toString(),
                    value: menuItems[index].toString()),
              ),
              label: &quot;Dropdown Select&quot;,
              values: selectedItems,
            ), 
  </code></pre>
  <p>I tried the Providers to achieve it but Providers does not work until I call the setters/getters of the Object on which Provider is registered. But FlutterMultiChipSelect needs the reference to a list. So I cannot call the setters explicitly.</p>