Question

我正在尝试使用Column来实现Text：

Column(
        children: <Widget>[
        Text('data from future function')
      ],
    ),

我无法从initState()获取数据，因为initState()只是void 如果我直接从函数中获取数据

Text(function)

我知道

功能实例

功能：

Future<double> calculate(int index) async {
    LocData _getUser = await getLoc();
    double uLat = _getUser.latitude;
    double uLng = _getUser.latitude;
    double pLat = parks[data].loc.lat;
    double pLng = parks[data].loc.lng;


    double dis = await Geolocator()
        .distanceBetween(uLat , uLng, uLng , pLat );
    return dis ;
  }

有什么办法可以将这些数据直接从函数中获取到文本wigdet？

Answer 1

有两种获取未来数据的方法。

选项1：

（带有2个子选项）

<button id='btnUEN' class='k-primary' onclick='getCategoriaByUEN('1','TEST'="" AND="" TEST')'="">TEST AND TEST</button>

选项＃2

使用FutureBuilder

class MyWidgetState extends State<MyWidget> {

  String _someAsyncData;

  @override
  void initState() {
    super.initState();

    // opt 1.
    aDataFuture.then((val) {  
      setState(() {
        _someAsyncdata = val;
      });
    });      

    // opt 2.
    _setAsyncData(aDataFuture);
  }

  void _setAsyncData(Future<String> someFuture) async {
    // void + async is considered a "fire and forget" call
    // part of opt. 2
    _someAsyncData = await someFuture;
    // must trigger rebuild with setState
    setState((){});
  }


  Widget build(BuildContext context) {
    return _someAsyncData == null ? Container() : Text('$_someAsyncData');
  }
}

Answer 2

这是完整的工作代码。

#[derive(Debug)]
enum Direction {
    Up(Point),
    Down(Point),
    Right(Point),
    Left(Point),
}

#[derive(Debug)]
struct Point {
    x: u32,
    y: u32,
}

#[derive(Debug)]
enum Keys {
    Up_key(String),
    Down_key(String),
    Right_key(String),
    Left_key(String),
}

impl Direction {
    fn match_direction(&self) -> Keys {
        match *self {
            Direction::Up(_) => Keys::Up_key(String::from("Up key is pressed")),
            Direction::Down(_) => Keys::Down_key(String::from("Down key is pressed")),
            Direction::Right(_) => Keys::Right_key(String::from("Right key is pressed")),
            Direction::Left(_) => Keys::Left_key(String::from("Left key is pressed")),
        }
    }
}

impl Keys {
    fn destruct(&self) -> &String {
        match *self {
            Keys::Up_key(ref s) => s,
            Keys::Down_key(ref s) => s,
            Keys::Left_key(ref s) => s,
            Keys::Right_key(ref s) => s,
        }
    }
}

fn main() {
    let test_1 = Direction::Right(Point { x: 1, y: 0 });
    let x = test_1.match_direction();
    println!("{:#?}", x);
    let k = x.destruct();
    println!("{}", k);
}

从将来的函数获取数据到文本小部件

2 个答案: