为什么 flutter 中的 setState function 不起作用？

Question

I am working with APIs and using a delete method to delete an item with a unique id from a list. The delete method is working but I need to reload the page everytime I want to see the results. I tried to add a setState() function inside a button and call the delete method from there but it is not working. I am not getting any errors however.

Delete method:

Future <void> deleteData(todo) async {
var urlToUpdate = Uri.parse('https://todoapp-api.apps.k8s.gu.se/todos/${todo.id}?key=${testKey}');

try {
  await http.delete(urlToUpdate, headers: {"Content-Type": "application/json"}, body: jsonEncode({
    "id": todo.id,
    "title": todo.title,
    "done": todo.done

  }));

} catch (err) {
  print(err);
}

}

setState method:

                child: IconButton(
                  onPressed: () {
                   setState(() {
                   var deleteTodo = TodoItem(id: id, title: '', done: false);
                   deleteData(deleteTodo);
                });
              },

I can't provide the whole code because it is too large but the delete method comes right after:

class _TodoListState extends State {

and before initState and Widget build.

Answer 1

setState method is used to reflect any change of data over some widget, if you need to remove a element from a list need has that element linked to a widget

example: If you has

listOfMovie = ['Avatar, Avengers', 'Dune', 'Hulk'];

ListView.builder(
                itemCount: listOfMovie.length,
                itemBuilder: (_, index) => Text(listOfMovie[index],
));

then

child: IconButton(
                  onPressed: () {
                   setState(() {
                   listOfMovie = ['Avatar, Avengers'];                   
                });
              },

If you notice listOfMovie is linked to ListView widget

Answer 2

you should wait until the deleteData finished.

After that, remove the local TodoItem from the list by yourself.

child: IconButton(
  onPressed: () async {
    var deleteTodo = TodoItem(id: id, title: '', done: false);
    await deleteData(deleteTodo);
    setState(() {
      => remove TodoItem from the local list =<
    });
  }

Because network request usually takes times. You should display something like CircularProgressIndicator when deleteData is running. But that's another story.