title: Change Widget on Dropdown onchange event
body: <p>I have a dropdown menu with several options. For sake of simplicity lets say they are: "A", "B" and "C".</p>
  
  <p>This is the snippet of my code:</p>
  
  <pre><code>children: &lt;Widget&gt;[
                        FormBuilder(
                          key: _fbKey,
                          autovalidate: true,
                          child: Column(
                            children: &lt;Widget&gt;[
                              FormBuilderDropdown(
                                attribute: "value",
                                decoration: InputDecoration(
                                labelText: "Choose something?"),
                                hint: Text('Select Option'),
                                validators: [FormBuilderValidators.required()],
                                items: user.option.map((v) {
                                  return DropdownMenuItem(
                                      value: v,
                                      child: ListTile(
                                        leading: Image.asset(
                                          'assets/img/image.png',
                                          width: 50,
                                          height: 50,
                                        ),
                                        title: Text("${v.option}"),
                                      ));
  
                                }).toList(),
                              ),
                            ],
                          ),
                         // if v.option == "A" is selected here build Widget A()
                         // if v.option == "B" is selected here build Widget B()
                         // if v.option == "C" is selected here build Widget C()
                        ),
  </code></pre>
  
  <p>So, based on Dropdown selection I want to render appropriate Widget.
  How can I build widget A if A is selected in the Dropdown menu, B if B is selected or C if C is selected?</p>
  
  <p>This has to change dynamically though, any help is good.</p>