title: How to open DropDownButton on init page
body: <p>i want to make a function for init <code>openDropDown();</code> when page loaded or tap on other widget</p>
  <p>I found this in <a href="https://stackoverflow.com/questions/57529394/how-to-open-dropdownbutton-when-other-widget-is-tapped-in-flutter">stackoverfow</a></p>
  <p>but its not working maybe its outdated. how can i achieve. with flutter 2.10
  here is my dropdown</p>
  <pre><code>DropdownButton(
                      isExpanded: true,
                      value: selectedValue,
                      items: [
                        for (var i = 0; i &lt; this.clients.length; i++)
                          DropdownMenuItem(
                              child: Text(this.clients[i]['name'].toString() +
                                  ' (' +
                                  this.clients[i]['wallet'].toString() +
                                  ') '),
                              value: this.clients[i]['id'].toString())
                      ],
                      onChanged: (String? newValue) {
                        setState(() {
                          selectedValue = newValue!;
                        });
                      },
                    ),
  </code></pre>