作为 Flutter 的新手，在 Flutter 应用程序中使用 setState 让我非常困惑。在下面的代码中，在 setState 中使用了 bool searching 和 var resBody。我的问题是为什么只有 searching 和 resBody 在 setState 中？为什么其他变量不可变？

var resBody;
bool searching =  false,api_no_limit = false;
String user = null;

Future _getUser(String text) async{
setState(() {
  searching = true;
});
user = text;
_textController.clear();
String url = "https://api.github.com/users/"+text;
  var res = await http
      .get(Uri.encodeFull(url), headers: {"Accept": 
           "application/json"});
  setState(() {
    resBody = json.decode(res.body);
  });
}

最佳答案

根据docs :

Calling setState notifies the framework that the internal state of this object has changed in a way that might impact the user interface in this subtree, which causes the framework to schedule a build for this State object.

因此，如果小部件的状态发生变化您必须调用 setState触发 View 的重建并立即查看新状态所暗示的更改。

无论如何，下面的代码 fragment 是等价的。

第一种情况(直接形式 flutter create <myproject>):

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {

    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

第二种情况:

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    _counter++;
    setState(() {});
  }

我不知道第一种情况的原因以及是否是使用 setState 的常规方式，我会说是因为代码的可读性。

https://stackoverflow.com/questions/51283077/