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为什么FutureBuilder在flutter没有收到呼叫?

flutter dart

Hesam · 技术社区 · 6 年前

_fetchPost() 每当我点击它。此方法调用 fetchPost() var post = ... 行。但是,我的问题是 builder

我是一个新手,所以我的代码是错误的吗?

void _fetchPost() {
    FutureBuilder<Post>(
      future: fetchPost(),
      builder: (BuildContext context, AsyncSnapshot<Post> snapshot) {
        if (snapshot.hasData) {
          String res = snapshot.data.parm1.toString() + snapshot.data.op + snapshot.data.parm2.toString();
          setState(() {
            _result = res;
          });
        } else if (snapshot.hasError) {
          setState(() {
            _result = snapshot.error;
          });
        }

        // By default, show a loading spinner
        return CircularProgressIndicator();
      },
    );
  }

  Future<Post> fetchPost() async {
    final response = await http.get('http://test.ethorstat.com/test.ashx');
    if (response.statusCode == 200) {
      // If server returns an OK response, parse the JSON
      var post = Post.fromJason(json.decode(response.body));
      return post;
    } else {
      // If that response was not OK, throw an error.
      throw Exception('Failed to load post!');
    }
  }

1 回复 | 直到 6 年前

creativecreatorormaybenot 6 年前

FutureBuilder 是一个 首先将其插入小部件树

未来建筑 build

class FetchWidget extends StatelessWidget {

  @override
  Widget build(BuildContext context) => FutureBuilder<Post>(
    future: fetchPost(),
    builder: (BuildContext context, AsyncSnapshot<Post> snapshot) {
      if (snapshot.hasData) {
        String res = snapshot.data.parm1.toString() + snapshot.data.op + snapshot.data.parm2.toString();
        setState(() { // setState will not work here, I only used this StatelessWidget to show what I mean with inserting it into the build tree
          _result = res;
        });
      } else if (snapshot.hasError) {
        setState(() {
          _result = snapshot.error;
        });
      }

      // By default, show a loading spinner
      return CircularProgressIndicator();
    },
  );

  Future<Post> fetchPost() async {
    final response = await http.get('http://test.ethorstat.com/test.ashx');
    if (response.statusCode == 200) {
      // If server returns an OK response, parse the JSON
     var post = Post.fromJason(json.decode(response.body));
     return post;
    } else {
      // If that response was not OK, throw an error.
     throw Exception('Failed to load post!');
    }
  }
}

这不会编译,因为我只将您的代码复制到 StatelessWidget setState “将[…]添加到小部件树”

或者你可以用普通的 async await

void _fetchPost() async {
  final Post fetchedPost = await fetchPost();
  final String res = fetchedPost.parm1.toString() + fetchedPost.op + fetchedPost.parm2.toString();
  setState(() {
    _result = res;
  });
}

fetchPost ,但是如果你想使用 builder .