我曾尝试在flutter中实现dropdownbutton,project.Dropdownbutton列表将由api填充。我已经从api中获取了列表。 但当我选择一个项目时,它不会显示。错误消息如下所示 The following assertion was thrown building FutureBuilder<List<Categories>>(dirty, state: _FutureBuilderState<List<Categories>>#09534):
There should be exactly one item wit